2010 Manual for Railway Engineering Volume 1 1 Track Introduction 3 Foreword Table of Contents Chapter 1 Roadway and Ballast (Chapters 3 and 10 were combined in 2000 to form Chapter 30) Chapter 4 Rail Chapter 5 Track Chapter 30 Ties General Subject Index Copyright © 2010 by the AMERICAN RAILWAY ENGINEERING AND MAINTENANCE-OF-WAY ASSOCIATION All rights reserved No part of this publication may be reproduced, stored in an information or data retrieval system, or transmitted, in any form, or by any means—electronic, mechanical, photocopying, scanning, recording, or otherwise—without the prior written permission of the publisher. Photocopying or electronic reproduction and/or distribution of this publication is a violation of USA and International Copyright laws and is expressly prohibited. Correspondence regarding copyright permission should be directed to the Director of Administration, AREMA, 10003 Derekwood Lane, Suite 210, Lanham, MD 20706 USA. ISSN 1542-8036 - Print Version ISSN 1543-2254 - CD-ROM Version 1 INTRODUCTION The AREMA Manual for Railway Engineering contains principles, data, specifications, plans and economics pertaining to the engineering, design and construction of the fixed plant of railways (except signals and communications), and allied services and facilities. This material is developed by AREMA technical committees, is published on the AREMA web site for comments and then is approved for publication in the Manual by the Association’s Board of Directors. Designated as Recommended Practice1, the contents of the Manual are published as a guide to railways in establishing their individual policies and practices relative to the subjects, activities and facilities covered in the Manual, with the aim of assisting them to engineer and construct a railway plant which will have inherent qualities of safe and economical operation as well as low maintenance cost. The AREMA Manual is not a maintenance manual per se since the development of standards or criteria for the maintenance of railway roadway, track and structures has always been considered to be the prerogative of the individual railways based on the nature and characteristics of their plant and operations and the specific characteristics of the geographical region or regions through which they operate. The above statements also apply to the AREMA Portfolio of Trackwork Plans, which is a companion volume to the AREMA Manual. The plans in the Portfolio relate to the design, details, materials and workmanship for frogs, switches, crossings and other special trackwork and are prepared and maintained by Committee 5 – Track, in addition to its Manual Chapter. 1 RECOMMENDED PRACTICE – A material, device, design, plan, specification, principle or practice recommended to the railways for use as required, either exactly as presented or with such modifications as may be necessary or desirable to meet the needs of individual railways, but in either event, with a view to promoting efficiency and economy in the location, construction, operation or maintenance of railways. It is not intended to imply that other practices may not be equally acceptable. © 2010, American Railway Engineering and Maintenance-of-Way Association i Introduction THIS PAGE INTENTIONALLY LEFT BLANK. © 2010, American Railway Engineering and Maintenance-of-Way Association ii AREMA Manual of Railway Engineering 1 FOREWORD This manual is current for the dates indicated on the title page of Volume I and is kept current by the issuance of annual updates. The first two editions of the Manual were issued in 1905 and 1907 as the “Manual of Recommended Practice for Railway Engineering and Maintenance of Way.” Both were bound volumes and published by the Association under its original name – American Railway Engineering and Maintenance-of-Way Association. In 1911, the Association changed its name to the American Railway Engineering Association and issued the third edition of its Manual. This edition, and the next one in 1915, was called the “Manual of the American Railway Engineering Association,” and was also a bound volume. The final bound volumes were published in 1921 and 1929 under the name “Manual of the American Railway Engineering Association for Railway Engineering.” A number of Manual updates were issued between some of the bound volumes. The first looseleaf edition of the AREMA Manual was issued in 1936 under the name “Manual for Railway Engineering,” the next in 1953. In 1961, the publication was reissued and called the “Manual of Recommended Practice for Railway Engineering.” The current title, “Manual for Railway Engineering,” was approved by the Board of Directors in 1970 and reverts to the former, simpler, more functional name although the contents are still recommended practice, as indicated in the preceding Introduction. In 1996 the Manual was given a complete facelift. Not only was the manual available in paper form, it was also available in an electronic version stored on a CD-ROM. The Manual was enlarged to an 8¹⁄₂ 11 inch format, perfect bound and divided into four volumes. For our users’ convenience, the Manual returned to a loose leaf four volume set in 2000. Each volume covers one of four general areas: Track, Structures, Infrastructure and Passenger, and Systems Management. The CD-ROM contains a complete version of the manual, which can be run on several platforms (Windows, Macintosh, and Unix). The Association also publishes the Portfolio of Trackwork Plans, which is a companion volume to the Manual for Railway Engineering. The Portfolio contains specifications and plans relating to the design of frogs, switches, crossings and other special trackwork. It was first issued about 1926 in cooperation with the Manganese Track Society. As shown on the following Contents pages, the AREMA Manual for Railway Engineering is issued in four volumes, each volume divided into chapters with numbers corresponding to the numbers of the standing technical committees charged with the primary responsibility for developing and maintaining the chapters. In addition, each volume contains a General Subject Index which augments the separate Table of Contents provided with each Chapter and Part of the Manual. To make the Manual easier to use and facilitate reference to parts of it, the committee identification number is carried throughout the publication by incorporating the number in the page numbering system. For complete information on the key features of the Manual, such as page numbering system, document dates, article dates, revision marks, and Proceedings references, the user is directed to the Introduction found in each Chapter. As stated earlier, updates to the Manual normally are issued annually. Beginning in 2001, revision sets to the looseleaf books are available. © 2010, American Railway Engineering and Maintenance-of-Way Association iii Foreword All holders of the Manual – individual AREMA members, individual nonmembers, railways, universities, governmental agencies, consulting engineers, constructors, supply companies, or other firms – are notified each year of the availability of the revised Manual and its cost. Manuals ordered during the normal Association year will be furnished complete for the dates indicated on the title page. Copies of the complete Manual may be purchased from Association Headquarters at the then current prices, which are subject to change without notice. To obtain current individual Chapters, please contact the Publications Department at AREMA at 301-459-3200. © 2010, American Railway Engineering and Maintenance-of-Way Association iv AREMA Manual of Railway Engineering TABLE OF CONTENTS Current until publication of next edition FOREWORD This Manual is divided into four Volumes which are further subdivided into Chapters and Parts. Each volume contains a general subject index covering data found in all volumes. Each Chapter and Part are prefaced by a Table of Contents. Because of numbering of Chapters to coincide in most cases with AREMA technical committees, there are no Chapters 3, 10, 19, 20, 21, 22, 23, 24, 25, 26, 29, 31 and 32. Committee 24 does not maintain a Manual Chapter. VOLUME 1 – TRACK Introduction Foreword Table of Contents Chapter 1 Roadway and Ballast Part 1 Roadbed Part 2 Ballast Part 3 Natural Waterways Part 4 Culverts Part 5 Pipelines Part 6 Fences Part 7 Roadway Signs Part 8 Tunnels Part 9 Vegetation Control Part 10 Geosynthetics Chapter 4 Rail Part 1 Part 2 Part 3 Part 4 Part 5 Part 6 Design of Rail Manufacture of Rail Joining of Rail Maintenance of Rail Miscellaneous Commentaries Track Part 1 Part 2 Part 3 Part 4 Tie Plates Track Spikes Curves Track Construction Chapter 5 © 2010, American Railway Engineering and Maintenance-of-Way Association v Table of Contents VOLUME 1 – TRACK (CONT) Part 5 Part 6 Part 7 Part 8 Part 9 Part 10 Track Maintenance Specifications and Plans for Track Tools Rail Anchors Highway/Railway Grade Crossings Design Qualification Specifications for Elastic Fasteners on Timber Cross Ties Miscellaneous Chapter 30 Ties Part 1 Part 2 Part 3 Part 4 Part 5 General Considerations Evaluative Tests for Tie Systems Solid Sawn Timber Ties Concrete Ties Engineered Composite Ties General Subject Index VOLUME 2 – STRUCTURES Chapter 7 Timber Structures Part 1 Material Specifications for Lumber, Timber, Engineered Wood Products, Timber Piles, Fasteners, Timber Bridge Ties and Recommendations for Fire-Retardant Coating for Creosoted Wood Part 2 Design of Wood Railway Bridges and Trestles for Railway Loading Part 3 Rating Existing Wood Bridges and Trestles Part 4 Construction and Maintenance of Timber Structures Part 5 Inspection of Timber Structures Part 6 Commentary Chapter 8 Concrete Structures and Foundations Part 1 Materials, Tests and Construction Requirements Part 2 Reinforced Concrete Design Part 3 Spread Footing Foundations Part 4 Pile Foundations Part 5 Retaining Walls, Abutments and Piers Part 6 Crib Walls Part 7 Mechanically Stabilized Embankment Part 10 Reinforced Concrete Culvert Pipe Part 11 Lining Railway Tunnels Part 12 Cantilever Poles Part 14 Repair and Rehabilitation of Concrete Structures Part 16 Design and Construction of Reinforced Concrete Box Culverts Part 17 Prestressed Concrete Part 19 Rating of Existing Concrete Bridges Part 20 Flexible Sheet Pile Bulkheads Part 21 Inspection of Concrete and Masonry Structures Part 22 Geotechnical Subsurface Investigation Part 23 Pier Protection Systems at Spans Over Navigable Streams Part 24 Drilled Shaft Foundations Part 25 Slurry Wall Construction Part 26 Recommendations for the Design of Segmental Bridges Part 27 Concrete Slab Track Part 28 Temporary Structures for Construction Part 29 Waterproofing © 2010, American Railway Engineering and Maintenance-of-Way Association vi AREMA Manual of Railway Engineering Table of Contents VOLUME 2 – STRUCTURES (CONT) Chapter 9 Seismic Design for Railway Structures Part 1 Seismic Design for Railway Structures Part 2 Commentary to Seismic Design for Railway Structures Chapter 15 Steel Structures Part 1 Design Part 3 Fabrication Part 4 Erection Part 6 Movable Bridges Part 7 Existing Bridges Part 8 Miscellaneous Part 9 Commentary Part 10 Bearing Design Part 11 Bearing Construction General Subject Index VOLUME 3 – INFRASTRUCTURE AND PASSENGER Commuter, Transit and High Speed Rail - Unified Table of Contents and Common Elements of Planning, Design and Operations Analyses for Passenger Rail Systems Chapter 6 Buildings and Support Facilities Part 1 Specifications and General Design Criteria for Railway Buildings Part 2 Design Criteria for Railway Office Buildings Part 3 Design Criteria for Spot Car Repair Shops Part 4 Design Criteria for Diesel Repair Facilities Part 5 Energy Conservation and Audits Part 6 Locomotive Sanding Facilities Part 7 Design Criteria for Railway Materials Management Facilities Part 8 Design Criteria for Railway Passenger Stations Part 9 Design Criteria for Centralized Maintenance-of-Way Equipment Repair Shops Part 10 Design Criteria for Observation Towers Part 11 Design Criteria for CTC Centers Part 12 Design Criteria for a Locomotive Washing Facility Part 13 Passenger Rail (Coach)/Locomotive Maintenance, Repair and Servicing Facilities Part 14 Selection and Maintenance of Roofing Systems Part 15 Inspection of Railway Buildings Part 16 Design Criteria for Main Line Fueling Facilities © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual of Railway Engineering vii Table of Contents VOLUME 3 – INFRASTRUCTURE AND PASSENGER (CONT) Chapter 11 Commuter and Intercity Rail Systems Part 1 Introduction Part 2 Corridor Planning Considerations Part 3 Track and Roadway Considerations Part 4 Facilities and Structural Considerations Part 5 Vehicle Considerations Part 6 Signals, Communications, and Propulsion Considerations Part 7 Maintenance of Way Considerations Chapter 12 Rail Transit Part 1 Introduction Part 2 Corridor Planning Considerations Part 3 Track and Roadway Considerations Part 4 Facilities and Structural Considerations Part 5 Vehicle Considerations Part 6 Signals, Communications, and Propulsion Considerations Part 7 Maintenance of Way Considerations Part 8 Embedded Track Chapter 14 Yards and Terminals Part 1 Generalities Part 2 Freight Yards and Freight Terminals Part 3 Freight Delivery and Transfer Part 4 Specialized Freight Terminals Part 5 Locomotive Facilities Part 6 Passenger Facilities Part 7 Other Yard and Terminal Facilities Chapter 17 High Speed Rail Systems Part 1 Introduction Part 2 Corridor Planning Considerations Part 3 Track and Roadway Considerations Part 4 Facilities and Structural Considerations Part 5 Vehicle Considerations Part 6 Signals, Communications, and Propulsion Considerations Part 7 Maintenance of Way Considerations Chapter 18 Light Density and Short Line Railways Part 1 General Engineering Part 2 Track Part 3 Bridges Part 4 Communication and Signals Chapter 27 Maintenance-of-Way Work Equipment Part 1 General Part 2 Roadway Machines © 2010, American Railway Engineering and Maintenance-of-Way Association viii AREMA Manual of Railway Engineering Table of Contents VOLUME 3 – INFRASTRUCTURE AND PASSENGER (CONT) Chapter 33 Electrical Energy Utilization Part 1 Factors to Consider in Making Electrification Economic Studies Part 2 Clearances Part 3 Recommended Voltages Part 4 Railroad Electrification Systems Part 5 Signal Compatibility with Alternating Current Railway Electrification Part 6 Power Supply and Distribution Requirements for Railroad Electrification Systems Part 7 Rail Bonding Part 8 Catenary and Locomotive Interaction Part 9 Ancillary Power Systems Part 10 Illumination Part 12 Power Supply and Electrification Systems General Subject Index VOLUME 4 – SYSTEMS MANAGEMENT Chapter 2 Track Measuring Systems Part 1 Definitions Part 2 Track Measuring Vehicles Part 3 Typical Uses of Data Collected by Track Measuring Vehicles Part 4 Measurement Frequency Practices for Track Geometry Measuring Vehicles Chapter 13 Environmental Part 1 Introduction Part 2 Environmental Review Considerations Part 3 Water and Wastewater Compliance Part 4 Air Quality Compliance Part 5 Waste Management Chapter 16 Economics of Railway Engineering and Operations Part 1 Railway Location Part 2 Train Performance Part 3 Power Part 4 Railway Operation Part 5 Economics and Location of Defect Detector Systems Part 6 Railway Applications of Industrial & Systems Engineering Part 7 Public Improvements – Their Costs and Benefits Part 8 Organization Part 9 Programming Work Part 10 Construction and Maintenance Operations Part 11 Equated Mileage Parameters Part 12 Accounting Part 14 Taxes Part 15 Planning, Budgeting and Control Chapter 28 Clearances Part 1 Clearance Diagrams – Fixed Obstructions Part 2 Equipment Diagrams Part 3 Methods and Procedures © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual of Railway Engineering ix Table of Contents VOLUME 4 – SYSTEMS MANAGEMENT (CONT) AAR Scale Handbook (Included for Information Only) Part 1 Specifications for the Location, Maintenance, Operation, and Testing of Railway Track Scales Part 2 Basic Specifications for the Manufacture and Installation of Railway Track Scales Part 3 Specifications for the Design and Installation of Low Profile, Pitless, and Instrumented Railway Track Scales Part 4 Rules for the Manufacture, Installation, Location, Operation and Testing of Railway Master Track Scales Part 5 Vehicle Scales Part 6 Hopper Type Scales Part 7 Belt Conveyor Scales (Amended 2009) Part 8 Mass Flow Meters (Added 2010) Part 9 Other Scales Guide for SI Metrication General Subject Index © 2010, American Railway Engineering and Maintenance-of-Way Association x AREMA Manual of Railway Engineering 1 CHAPTER 1 ROADWAY AND BALLAST1 TABLE OF CONTENTS Part/Section Description Page 1 Roadbed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Exploration and Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Construction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-1 1-1-3 1-1-12 1-1-38 1-1-53 2 Ballast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 Substructure Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Scope (1991) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Property Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 Production and Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6 Loading (1988) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7 Inspection (1988) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.8 Sampling and Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.9 Measurement and Payment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.10 Maintenance Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.11 Sub-ballast Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-1 1-2-4 1-2-5 1-2-9 1-2-9 1-2-10 1-2-13 1-2-13 1-2-14 1-2-14 1-2-15 1-2-15 1-2-19 Natural Waterways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Drainage Basin Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Capacity of Waterway Openings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Basic Concepts and Definitons of Scour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 Calculating Scour. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6 Protecting Roadway and Bridges From Scour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.7 Means of Protecting Roadbed and Bridges from Washouts and Floods . . . . . . . . . . . . . . . . 1-3-1 1-3-4 1-3-5 1-3-7 1-3-20 1-3-25 1-3-60 1-3-148 3 1 The material in this and other chapters in the AREMA Manual for Railway Engineering is published as recommended practice to railroads and others concerned with the engineering, design and construction of railroad fixed properties (except signals and communications), and allied services and facilities. For the purpose of this Manual, RECOMMENDED PRACTICE is defined as a material, device, plan, specification, principle or practice recommended to the railways for use as required, either exactly as presented or with such modifications as may be necessary or desirable to meet the needs of individual railways, but in either event, with a view to promoting efficiency and economy in the location, construction, operation or maintenance of railways. It is not intended to imply that other practices may not be equally acceptable. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-i 1 3 TABLE OF CONTENTS (CONT) Part/Section 3.8 3.9 4 Description Page Construction and Protection of Roadbed Across Reservoir Areas . . . . . . . . . . . . . . . . . . . . Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-150 1-3-159 Culverts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Location and Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Specifications for Placement of Reinforced Concrete Culvert Pipe . . . . . . . . . . . . . . . . . . . 4.3 Specifications for Prefabricated Corrugated Steel Pipe and Pipe-arches for Culverts, Storm Drains, and Underdrains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Specifications for Coated Corrugated Steel Pipe and Arches. . . . . . . . . . . . . . . . . . . . . . . . 4.5 Standard Specification for Corrugated Aluminum Alloy Pipe . . . . . . . . . . . . . . . . . . . . . . . 4.6 Specifications for Corrugated Structural Steel Plate Pipe, Pipe-arches, and Arches. . . . . 4.7 Specifications for Corrugated Structural Aluminum Alloy Plate Pipe, Pipe-arches, and Arches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8 Hydraulics of Culverts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9 Design Criteria for Corrugated Metal Pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.10 Design Criteria for Structural Plate Pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.11 Culvert End Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.12 Assembly and Installation of Pipe Culverts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.13 Earth Boring and Jacking Culvert Pipe through Fills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.14 Culvert Rehabilitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.15 Specification for Steel Tunnel Liner Plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.16 Construction of Tunnel Using Steel Tunnel Liner Plates . . . . . . . . . . . . . . . . . . . . . . . . . . 4.17 Culvert Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.18 Perforated Pipe Drains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-1 1-4-6 1-4-9 1-4-26 1-4-29 1-4-56 1-4-65 1-4-68 1-4-70 1-4-75 1-4-77 1-4-82 1-4-90 1-4-91 1-4-100 5 Pipelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Specifications for Pipelines Conveying Flammable Substances. . . . . . . . . . . . . . . . . . . . . . 5.2 Specifications for Uncased Gas Pipelines within the Railway Right-of-Way . . . . . . . . . . . 5.3 Specifications for Pipelines Conveying Non-Flammable Substances . . . . . . . . . . . . . . . . . 5.4 Specifications for Overhead Pipelines Crossings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 Specifications for Fiber Optic “Route” Construction on Railroad Right of Way . . . . . . . . 1-5-1 1-5-3 1-5-11 1-5-23 1-5-29 1-5-31 6 Fences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Specifications for Wood Fence Posts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 Specifications for Concrete Fence Posts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4 Specification for Metal Fence Posts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 Specifications for Right-of-way Fences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6 Stock Guards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.7 Methods of Controlling Drifting Snow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.8 Specifications for Snow Fences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6-1 1-6-3 1-6-4 1-6-6 1-6-10 1-6-13 1-6-20 1-6-21 1-6-24 7 Roadway Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1 Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7-1 1-7-2 1-7-4 1-7-4 1-4-9 1-4-17 1-4-17 1-4-24 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-ii AREMA Manual for Railway Engineering TABLE OF CONTENTS (CONT) Part/Section Description Page 8 Tunnels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1 Scope (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 Design (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3 Construction (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4 Measurement and Payment (1982). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5 Lining (1982) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.6 Ventilation (1982) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.7 Increasing Clearances In Existing Tunnels (1982) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8-1 1-8-2 1-8-2 1-8-3 1-8-6 1-8-6 1-8-6 1-8-7 9 Vegetation Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1 Rationale and Scope of Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2 Preparing a Vegetation Control Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3 Executing a Vegetation Control Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.4 Evaluating Results of a Vegetation Control Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.5 Glossary (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.6 Lead Agencies (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.7 Commentary (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9-1 1-9-2 1-9-2 1-9-11 1-9-14 1-9-16 1-9-17 1-9-20 10 Geosynthetics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.1 Geotextile Specifications for Railroad Track Separation/Stabilization Applications . . . . . 10.2 Geotextile Specifications for Railroad Drainage Applications . . . . . . . . . . . . . . . . . . . . . . . 10.3 Geotextile Specifications for Railroad Erosion Control Applications . . . . . . . . . . . . . . . . . . 10.4 Geocomposite Drainage System Specifications for Railroad Applications . . . . . . . . . . . . . . 10.5 Cellular Confinement System Specification for Railroad Use . . . . . . . . . . . . . . . . . . . . . . . 10.6 Geogrid Specifications for Ballast and Sub-Ballast Reinforcement . . . . . . . . . . . . . . . . . . . 1-10-1 1-10-3 1-10-9 1-10-15 1-10-20 1-10-24 1-10-28 Glossary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-G-1 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-R-1 1 3 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-iii INTRODUCTION The Chapters of the AREMA Manual are divided into numbered Parts, each comprised of related documents (specifications, recommended practices, plans, etc.). Individual Parts are divided into Sections by centered headings set in capital letters and identified by a Section number. These Sections are subdivided into Articles designated by numbered side headings. Page Numbers – In the page numbering of the Manual (1-2-1, for example) the first numeral designates the Chapter number, the second denotes the Part number in the Chapter, and the third numeral designates the page number in the Part. Thus, 1-2-1 means Chapter 1, Part 2, page 1. In the Glossary and References, the Part number is replaced by either a “G” for Glossary or “R” for References. Document Dates – The bold type date (Document Date) at the beginning of each document (Part) applies to the document as a whole and designates the year in which revisions were last made somewhere in the document, unless an attached footnote indicates that the document was adopted, reapproved, or rewritten in that year. Article Dates – Each Article shows the date (in parenthesis) of the last time that Article was modified. Revision Marks – All current year revisions (changes and additions) which have been incorporated into the document are identified by a vertical line along the outside margin of the page, directly beside the modified information. Proceedings Footnote – The Proceedings footnote on the first page of each document gives references to all Association action with respect to the document. Annual Updates – New manuals, as well as revision sets, will be printed and issued yearly. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-iv AREMA Manual for Railway Engineering 1 Part 1 Roadbed1 — 2007 — FOREWORD Since the development of soil and foundation engineering as an important branch of civil engineering during the past few decades, earth and rock have come to be treated as construction materials. They have properties which can be evaluated and they are subject to strains and failures in the same way as other building materials. Earth and rock are different, however, from such materials as steel and concrete in one fundamental way of which the designer should always be aware: each soil and rock deposit is extremely variable and has its own characteristics which reflect its origin and the factors affecting it since. As a result, investigation and testing are uniquely important if soils and rock are to be used economically and safely in engineering work. This Part of the Manual is prepared with recognition of the importance of geotechnical knowledge in the design, construction and maintenance of track. The subgrade is considered to be as important to track performance as the rail and ballast. Keeping this balanced point of view in mind, an engineered approach is presented for many roadbed problems rather than reference to standard practice. The choice of available methods is given along with an evaluation of the judgment factors involved in many of the questions relating to the design and construction of new roadbed and the upgrading and maintenance of existing roadbed. Considerations such as drainage and slope stability which affect the roadbed directly but are centered outside its physical limits are included. Because of the variety of foundation conditions which occur and their associated problems, a number of references are given. Details of methods are presented only when adequate information is hard to find elsewhere. Specialized help is advisable when a detailed appraisal of the suitability and performance of particular deposits is required. 1 References, Vol. 74, 1973, p. 55; Vol. 77, 1976, p. 237; Vol. 87, 1986, p. 35; Vol. 89, 1988, pp. 40, 41. Reapproved with revisions 1988. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-1 1 3 Roadway and Ballast TABLE OF CONTENTS Section/Article Description Page 1.1 Exploration and Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.1 General (2000) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.2 Preliminary Exploration (2000). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.3 Detailed Geotechnical Exploration in Soil (2000). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.4 Detailed Geotechnical Exploration in Rock (2000). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.5 Construction Material Sources (2000). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-3 1-1-3 1-1-3 1-1-4 1-1-6 1-1-8 1.2 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.1 General (2002) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.2 Cuts (2002) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.3 Fills (2002) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.4 Drainage (2003) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-12 1-1-12 1-1-13 1-1-23 1-1-32 1.3 Construction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.1 General (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.2 Contract Documents (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-39 1-1-39 1-1-39 1.4 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-55 1.4.1 Maintenance of Roadbed (2007). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-55 1.4.2 Maintenane of Rock Slopes (2007). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-64 1.4.3 Maintenance of Earth Slopes (2007) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-65 1.4.4 Widening of Cuts (2007) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-67 1.4.5 Drainage and Erosion Control (2007) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-68 1.4.6 Methods of Opening Snow Blockades (2007) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-70 LIST OF FIGURES Figure 1-1-1 1-1-2 1-1-3 1-1-4 1-1-5 1-1-6 1-1-7 1-1-8 1-1-9 1-1-10 1-1-11 1-1-12 1-1-13 1-1-14 1-1-15 Description Page Cut and Fill Section Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Width of Rock Cut Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Variable Slope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Uniform Slope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Permanent Bench . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Temporary Bench . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Zoning of Rock Fill Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Interception of Sidehill Seepage by Subdrainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lowering of Ground Water In a Wet Cut. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lowering of Ground Water in Cut to Fill Transition (Longitudinal). . . . . . . . . . . . . . . . . . . . . Lowering of Ground Water in Cut to Fill Transition (Sidehill) . . . . . . . . . . . . . . . . . . . . . . . . . Example of Distorted Roadbed Cross Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example Cross Section of Displaced Roadbed and Ballast Pocket . . . . . . . . . . . . . . . . . . . . . . . Method of Marking Track for Treatment of Frost Heaving . . . . . . . . . . . . . . . . . . . . . . . . . . . . General Approach to Rock Fall Hazard Management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-13 1-1-17 1-1-19 1-1-20 1-1-21 1-1-21 1-1-29 1-1-37 1-1-37 1-1-38 1-1-38 1-1-57 1-1-57 1-1-63 1-1-65 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-2 AREMA Manual for Railway Engineering Roadbed LIST OF TABLES Table 1-1-1 1-1-2 1-1-3 1-1-4 1-1-5 1-1-6 1-1-7 1-1-8 1-1-9 1-1-10 1-1-11 1-1-12 Description Sources of Site Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Procedures for Soil Exploration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Standard Procedures for Soil Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Technical Descriptions of Cores or Fresh Exposures of Rock . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical Tests for Rock Samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Factors Affecting Width of Cut . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Factors Affecting Base Width of Rock Cuts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Factors for Rock Slopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Improvement of Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Soil Groups, Their Characteristics and Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Guidelines for Limiting Velocities to Prevent Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Potential Methods for Stabilizing Earth Slopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 1-1-8 1-1-10 1-1-10 1-1-11 1-1-12 1-1-14 1-1-17 1-1-22 1-1-27 1-1-30 1-1-33 1-1-66 SECTION 1.1 EXPLORATION AND TESTING 1 1.1.1 GENERAL (2000) a. Roadbed construction and maintenance costs can be reduced by using an effective exploration and testing program as the first and most important step of the design process. b. Site investigations are usually done in two phases: (1) PRELIMINARY SITE INVESTIGATION - Review of information available from published sources and previous investigations, supplemented by site reconnaissance. Roadbed maintenance investigations should include a history of slow orders, surfacing operations, drainage condition changes, apparent failure mechanism, failure frequency, and apparent correlation with weather. (2) DETAILED SITE INVESTIGATION - Collection and analysis of detailed information on soil, rock, groundwater, surface drainage, and topography determined by exploration, sampling, and laboratory testing. Detailed maintenance information should include investigation of the ballast roadbed interface, particularly "ballast pockets", their density and drainage. 1.1.2 PRELIMINARY EXPLORATION (2000) 1.1.2.1 Information Available a. New Construction - Geological, topographic, climatic, and seismic information from published sources is useful in planning exploration work and interpreting site observations. See Table 1-1-1. b. Maintenance - Review the information for new construction as noted in Table 1-1-1, supplemented by a performance history of the problem area. Include a review of the slow order history, surfacing operations, track geometry history, traffic density history, drainage conditions, apparent failure mechanisms, frequency of failure, and apparent correlation with weather. Some problem maintenance areas will become readily apparent when the above information is graphed with respect to time. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-3 3 4 Roadway and Ballast 1.1.2.2 Photogrammetry 1.1.2.2.1 New Construction a. Aerial photographs at various scales are available for most locations. Photo mosaics can be assembled and used in studying the site conditions. Photos on a large scale may be required for more detailed studies and can be obtained on order. b. Stereo-optic viewing of overlapping aerial photographs assists inrecognizing land forms, landslides, general soil types, drainage, and erosional features. Photo interpretation can aid in supplementing ground observations and in planning an appropriate detailed site investigation program. Since aerial photographs only showconditions at or near the ground surface, they cannot be used independently to give detailed subsurface information for design. c. Other techniques for obtaining general surface conditions and landform characteristics as well as more detailed information for track layout, drainage design, and asset location may include ground or aerial based LIDAR (Light Detection and Ranging) and video based surveying techniques. 1.1.2.2.2 Maintenance Aerial photographs are not routinely utilized. Soil Conservation Service photographswith adjacent soil types superimposed on them may be useful. Site specific aerial photographs can provide useful information relative to the local surface drainage conditions. 1.1.2.2.3 Site Reconnaissance a. New Construction - A thorough reconnaissance of the site is necessary to assess the existing conditions and establish the need for appropriate detailed tests. Effective site reconnaissance requires close observation of apparent surface soil conditions and rock exposures, as well as ground surface and drainage patterns. Observation of nearby excavations may provide useful information. A particular warning is given by the presence of soft ground, soils, which become weak when disturbed, ground water seepage, and eroding soil banks. b. Maintenance - A thorough reconnaissance of the existing roadbed is necessary to understand the true nature of the roadbed failure mechanism. This will include examination of the roadbed cross section, profile, alignment, track geometry, and surface drainage. Look for ground water seepage, roadbed erosion, track squeeze, slides, irregularity of the shoulder vegetation lines, and any site specific anomalies which may be influencing the site conditions. Trackside trees and pole line are excellent indicators of slope movement in a maintenance situation. 1.1.3 DETAILED GEOTECHNICAL EXPLORATION IN SOIL (2000) 1.1.3.1 General Soil Exploration Criteria Construction or maintenance of a roadbed frequently involves an interface with, or the excavation of, either naturally deposited or mechanically placed soils. The ultimate stability of the roadbed will be governed by the engineering characteristics and suitability of these soils. An adequate exploration program should be developed with the assistance of a qualified geotechnical engineer to define these parameters. Procedures utilized can include, but should not be limited to, those listed in Table 1-1-2. 1.1.3.2 Embankment (Fill) Foundations 1.1.3.2.1 New Construction a. Embankment foundations are explored so that the embankments are designed to avoid failure or compensate for settlement of the subsoil. The subsurface and surface drainage conditions must be © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-4 AREMA Manual for Railway Engineering Roadbed determined to avoid conditions such as sinkholes, springs under the fill, excessive pore water pressures in the foundation soils, and inadvertent interception of an underground aquifer. b. Depending on the material conditions encountered, the exploration and sampling requirements can be quite different. When granular material is encountered in the embankment foundation the exploration and sampling may be less then that required for cohesive soils but should be sufficient to confirm the range of the strength parameters. The depth and number of borings should be sufficient to provide the design information required. c. Areas of new construction immediately adjacent to existing track, such as new sidings and auxiliary main lines, do not require detailed exploration. These areas would normally require few widely spaced borings unless specific problem areas warrant further examination. On new construction to avoid major problems at tie ins attention should be paid to grubbing, stripping, and benching. 1.1.3.2.2 Maintenance The First order of business in a catastrophic failure on an existing railroad embankment is to get the railroad open for service. This usually doesn't allow sufficient time to do a thorough detailed site exploration prior to reconstructing the roadbed. Many troublesome maintenance failures are of a "creeping" type. These manifest themselves in a poor or degrading track alignment and surface. This type of failure often requires substantial exploration to determine the failure mechanisms. Failure mechanism exploration is site specific and may be very complicated. Borings are required of sufficient depth to intercept any failure planes, as a minimum at least below the embankment foundation or depth of failure plane whichever is greater. Exploration of maintenance failure mechanisms should not be limited solely to boring. Other methods may include any of the following; cross trenches or test pits, inclinometer, piezometer, or examination of the exposed failed embankment surfaces. 1.1.3.3 Cuts 1 1.1.3.3.1 New Construction a. b. c. Locations of proposed cut slopes are explored to design stable slopes and berms. In fine grained soils this requires suitable samples and appropriate laboratory tests to determine the shear strength characteristics of the materials. In cohesionless, disturbed samples and standard penetration test values are usually adequate. In cohesive soils it may be necessary to obtain undisturbed tube samples for tests which include classification, water content, and shear strength. Most importantly, exploration should be carried out at least below the bottom of the proposed cut or deeper if recommended by the geotechnical engineer. The exploration should determine the level of the groundwater table and efforts should be made to determine whether or not a perched water table exists. This may require a rather elaborate investigation, including the installation of standpipes at selected locations. Particular care should be taken to identify cohesionless layers that might become water-bearing at certain times or seasons. These can be expected to erode back from the face of the cut, causing local instability or a build-up of excess water pressure leading to a failure. Sufficient information should be obtained to classify the materials likely to be encountered, determining suitability of the materials for use in adjacent fills. A knowledge of the geology of the area is useful to indicate the necessity for additional tests of a specialized nature. Some geological formations have swelling characteristics and should be investigated. 1.1.3.3.2 Maintenance Typical failures in an existing cut include filled or non-functional ditches, surface water eroding the slope, shallow ballast sections, and inadequate subgrade support. An initial means for assessing the potential cause of a problem begins with performing a field observation. The question to be answered is, "What has caused a previously stable slope to fail?" Examine the top of the slope. Check the slope for chemical changes in soil properties, seepage and drainage changes, and additional loading surcharge above the top of slope. Use cross trenches, inclinometer, aerial photography, and previous area history to help determine the failure mechanism. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-5 3 4 Roadway and Ballast 1.1.3.4 Laboratory Testing and Analysis Appropriate laboratory tests and analysis methods will be dependent on the soils encountered, the desired construction or existing roadbed configuration, and the sampling methods utilized. These can include, but should not be limited to, the tests listed in Table 1-1-3. 1.1.4 DETAILED GEOTECHNICAL EXPLORATION IN ROCK (2000) 1.1.4.1 General Rock Exploration Criteria 1.1.4.1.1 New Construction a. When construction of roadbed involves an interface with natural rock bedding (embankment fills), or requires rock excavation and slope design (rock cuts), it is imperative that adequate insitu and laboratory information is obtained on the structural nature of the rock. Beyond providing for sound design, preliminary information will provide realistic parameters for estimating both construction costs and schedules. b. The methods of obtaining information on rock formations can be grouped into two (2) categories: 1) empirical - a study based solely on existing geological information and visible surface features, or 2) intrusive - a study in which existing information is supplemented by subsurface exploration and testing of the rock mass. c. The ultimate stability of a roadbed engineered through rock will be defined by the nature of any structural discontinuities which may exist at the location. Major rock cuts will typically require detailed subsurface exploration. Minor rock cuts often may be designed by an experienced engineer without subsurface exploration. Both methods are valid provided that an educated decision is made for appropriateness. The planning and execution of this exploration should be conducted with the assistance of a qualified Engineering Geologist. 1.1.4.1.2 Maintenance When roadbed maintenance problems exist as a result of existing rock cut slopes, or the failure of the embankment bedding structure, it may be necessary to assess the stability of the associated rock structures prior to undertaking corrective measures. Such assessments may require an intrusive study, but in many cases can be explored by a detailed site investigation of geologic surface features and a thorough review of original construction plans and exploration records. 1.1.4.2 Rock Exploration Methodology 1.1.4.2.1 New Construction a. The first step of the exploration process involves a detailed geological reconnaissance and mapping of site. Utilize visible outcroppings to predict the strike and dip of beds, as well as to identify obvious faults, discontinuities, jointing and fracture patterns. Utilize auger borings or test trenches through soil overburden, to determine initial rock surface profiles when rock is not visible. b. From this information an exploration plan should be devised which will provide a continuity of data regarding structure of rock. Undisturbed rock samples should be obtained from fresh unweathered exposures at the site, or from core samples recovered from borings. To the extent possible, the subsurface exploration program should be designed in an attempt to reveal potential structural discontinuities. Core recovery should be monitored by a qualified Engineering Geologist, so that necessary changes may be made to maximize recovery of useful data. The spacing and depth of bores will be project specific. All bores should be advanced to a depth which is sufficient to verify the competency of the proposed subgrade. At minimum, this depth will be the proposed subgrade elevation. On cuts of significant depth, exploration should extend well outside the proposed centerline as significant discontinuities may exist which could affect design of the upper portions of slopes. Detailed drilling logs should be maintained and the recovered samples should be preserved for a mutually agreed upon period of time. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-6 AREMA Manual for Railway Engineering Roadbed c. Undisturbed core samples are typically obtained using a standard diamond-tipped rock boring machine equipped with a continuous recovery tube. The minimum size for a recovery tube should be type BX (15/8"), with sizes NQ (2") and NX (2-1/8") being more commonly used. For projects in areas of suspected geologic irregularities use of even larger recovery tubes may be of value. Such a determination can be based on the preliminary geologic data for the site. 1.1.4.2.2 Maintenance Exploration of rock as related to roadbed maintenance problems, will rely primarily on visual examination of exposed rock surfaces. When existing surface conditions do not obviously reveal the causes of the problem, it may be necessary to use intrusive exploration techniques to identify the depths at which competent material is present. This may reveal the presence of faults, fracture patterns, and structurally weak layers that could affect the stability of the associated rock mass. 1.1.4.3 Examination and Testing a. Rock samples and cores provide an important record of visible structura information. Samples should be examined and a final geologic log accurately prepared. See Table 1-1-4 for a list of recommended descriptive terminology. The resulting data should be consolidated in a usable format which may include detailed boring logs, and cross-sectional mapping of the rock structure. In general this detailed information provides the primary tool for the Design Engineer in predicting the theoretical structural behavior of the rock mass. This base information provides only qualitative design values which are used in part for detailed strength and stability analysis . b. Representative samples from the rock cores can be utilized to determine the strength and deformation characteristics of the rock as well as its potential for weathering. See Table 1-1-5 for a list of possible test methods. These tests can provide much more precise design values, but test suitability is job specific and should be determined with the assistance of an Engineering Geologist. c. Since many variables exist regarding rock mechanics, providing the most comprehensive information available in a usable format will greatly assist the Design Engineer in development of a viable design or corrective scheme. 1 3 1.1.5 CONSTRUCTION MATERIAL SOURCES (2000) 1.1.5.1 Site Sources Borrow areas for soil embankment fill construction are often preliminarily explored by auger boring. The suitability of such soils can be further verified by utilizing the sampling and testing procedures outlined elsewhere in this section. 1.1.5.2 Commercial Sources Select granular fill materials supplied by off-site commercial sources for use in embankment fill construction are typically produced to defined specifications and should be tested to ensure consistent quality control. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-7 4 Roadway and Ballast Table 1-1-1. Sources of Site Information Type of Information and Usage Source Geological Surveys: National: National: Indexes to existing geologic mapping United States - U.S. Geological Survey and exploration. Canada - Canadian Geological Survey Detailed maps of Topography, Surface Mexico - Colegio de Ingenieros de Mineros, Metalurgistas y and Subsurface structural Geo’logos de Mexico information. Localized: Correlation and characteristics of State and Provincial Geological geological deposits. Surveys and Societies Localized: Maps, bulletins, and reports on Other: locally unique subjects. Independent Geologic Societies Existing & Historical Land Use: Maps and documents available on exploration and use of mineral and geologic resources. Information on the structural nature of deposits, and identification of subsurface excavations and discontinuity. United States - Bureau of Land Management, Department of Surface Mining, Department of Mine Reclamation, American Petroleum Institute Canada - Department of Energy, Mines & Resources (DEM&R) Mexico - Com. de Fomento Minero Instituto Nacional de Statistica Geografica Informativa (INEGI) Generalized Soil Information: Maps and reports on surface conditions with summaries of subsurface geological conditions. National: United States - Department of Agriculture Soil Conservation Service Canada - DEM&R, Environment Canada Mexico - ENEGI Localized: State and Provincial Conservation and Agricultural Agencies Aerial Photographs: See Section:1.2.2 National: United States - Department of Agriculture Soil Conservation Service Canada - DEM&R, Environment Canada Mexico - ENEGI, Cia Topografica, Ingenieria y Aerofotogrametri Localized: State and Provincial Agricultural or Economic Development Agencies © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-8 AREMA Manual for Railway Engineering Roadbed Table 1-1-1. Sources of Site Information (Continued) Type of Information and Usage Atomospheric Conditions: Information on rainfall and temperature variation necessary for the analysis of drainage, weathering and frost penetration Source National: United States - National Oceanic & Atmospheric Administration, National Weather Service Canada - Environment Canada Mexico - Servicio Meteorologico, Servicio a la Navegacion en el Espacio Aereo Mexicano Localized: State and Provincial Conservation and Agricultural Agencies Building and Seismic Design Codes: United States - State and Municipal Building Information on construction methods Code Agencies Canada - National Building Code or design requirements. Seismic considerations. Mexico - Departamento del Distrito Federal 1 3 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-9 Roadway and Ballast Table 1-1-2. Procedures for Soil Exploration Procedure ASTM Method Site Characterization for Engineering, Design & Construction Purposes D 420 Soil Investigation and Sampling by Auger Borings D 1452 Penetration Test and Split-barrel Sampling of Soils D 1586 Thin-wall Tube Geotechnical Sampling of Soils D 1587 Field Vane Shear Test in Cohesive Soils D 2573 Deep, Quasi-Static, Cone & Friction – Cone Penetration Tests of Soil D 3441 Table 1-1-3. Standard Procedures for Soil Testing Procedure ASTM Method Material Finer than No. 200 Sieve in Mineral Aggregates by Washing C 117 Particle Size Analysis of Soils D 422 Laboratory Compaction Characteristics of Soil using Standard Effort D 698 Specific Gravity of Soils D 854 Laboratory Compaction Characteristics of Soil using Modified Effort D 1557 Density and Unit Weight of Soil in Place by the Sand-Cone Method D 1556 Unconfined Compressive Strength of Cohesive Soil D 2166 Density and Unit Weight of Soil in Place by the Rubber-Balloon Method D 2167 Laboratory Determination of Water (moisture) Content of Soils & Rock D 2216 One-Dimensional Swell or Settlement Potential of Cohesive Soils D 4546 Classification of Soils for Engineering Purposes D 2487 Description & Identification of Soils (visual-manual procedure) D 2488 Liquid Limit, Plastic Limit, and Plasticity Index of Soils D 4318 Maximum Index Density & Unit Weight of Soils Using a Vibratory Table D 4253 Minimum Index Density & Unit Weight of Soils and Calculation of Relative Density D 4254 Consolidated-Undrained Triaxial Compression Test of Cohesive Soils D 4767 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-10 AREMA Manual for Railway Engineering Roadbed Table 1-1-4. Technical Descriptions of Cores or Fresh Exposures of Rock Feature Discontinuity - Type Description or Occurrence Importance Influence on Permeability, Joints Faults Strength, and Deformation of Bedding Planes (as in Sedimentary Rock) the Rock Mass. Cleavage Planes (as in Slates) Fracture with Striations or Slickenslides (from past movement) - Position Closeness and Orientation of Joints Thickness of Bedding Layers Length of Core Pieces (as influenced by drilling techniques) Dip or Angle of Inclination from Horizontal Of Major Importance in Cut Slopes and Tunnels. - Surface Fit of Surfaces - Tight or Open Shape - Plane, Curved, or Irregular Texture - Slick, Smooth, or Rough Governs amount of Interlocking and Apparent Shearing Resistance along Fractures. Filling Material May Govern Movement along Properties - Type, Hardness, Thickness, Discontinuities. Variations Origin - Derived from Rock by Alteration, or from External Source Rock Type and Texture Geologic Name Based on Mineral Composition, Texture and Origin Size and Angularity of Grains, Type of Fracture, Luster, Lamination Texture - Interlocking Grains Cemented or Laminated - Foliated, Preferred Orientation Rock Hardness Core Recoverability 1 3 Relative hardness (give basis of comparison) Variations Due to Changes in Rock Type, Weakened Rock, Weathering or Decomposition Products Severe Design and Construction Problems may Arise when Hardness of Parts of Rock Mass Differ Radically from Average Value. Total Core Recovery (%) Rock Quality Designation (RQD) Identifies Weak Core Classifies Relative Strength 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-11 Roadway and Ballast Table 1-1-5. Typical Tests for Rock Samples Procedure ASTM Method Specific Gravity and Absorption of... - Coarse Aggregate - Fine Aggregate Soundness of Aggregates by use of Sodium Sulfate or Magnesium Sulfate Resistance to Degradation by Impact and Abrasion using the Los Angeles Machine of... - Large Size Coarse Aggregate - Small Size Coarse Aggregate Petrographic Examination of Aggregate Compression - Uniaxial C 127 C 128 C 88 To Indicate Rock’s Resistance to Weathering C 535 C 131 To serve as a measure of degradation of mineral aggregates from a combination of actions including abrasion or attrition, impact and grinding. C 295 See text Special - Triaxial Stength of Undrained Rock Core Specimens without Pore Pressure Measurements Comments D 2664 SECTION 1.2 To Classify Rock for Strength and Deformation Properties. Utilizes Diamond Drilled Cores. To Find Angle of Shearing Resistance of Weak Rock Material with Random Orientation of Joints. Range of Normal Stresses Occurring in Field are Applied. DESIGN 1.2.1 GENERAL (2002) a. This section describes material and drainage issues that need to be evaluated as part of the design of cuts and fills along railroad roadways. It is assumed that the general project alignment has been selected, field exploration and soil sampling have been performed, and laboratory testing is completed prior to commencing with the final design. Issues for consideration in design include horizontal and vertical alignments and typical sections all of which are influenced by traffic considerations, topographical features, drainage, and soils and rock data. Environmental conditions such as drainage, wetlands and contaminated soils also influence the design. b. Subjects which could be common to both design and maintenance are found in Section 1.4, Maintenance. These subjects include unstable subgrade conditions, frost heaving of tracks, rock falls, both cut and fill slope failures, and erosion control. The issues which are discussed in Section 1.2, Design, address how soils and drainage influence cuts and fills. 1.2.2 CUTS (2002) 1.2.2.1 General a. Definition: Cuts are made when excavations are required through hills to provide roadbed grades and to acquire materials for use when constructing fill sections. Materials encountered in cuts can consist of cohesive soils, cohesionless soils, rock or combinations thereof. The general components of a cut (and fill) © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-12 AREMA Manual for Railway Engineering Roadbed section consist of the back slope(s), benches (if required), foreslope(s), ditches, and the top of subgrade (track roadbed) as presented in Figure 1-1-1. The “cut” width is the total of the backslope(s), ditches, foreslope(s) top of subgrade widths, and interceptor ditches where required for the section(s). The purpose of each of these segments are defined in Table 1-1-6. 1 Figure 1-1-1. Cut and Fill Section Components 3 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-13 Roadway and Ballast Table 1-1-6. Factors Affecting Width of Cut SEGMENT PURPOSE WHERE PROVIDED WIDTH & PROFILE A. Top of Subgrade To provide a base for sub- Throughout cut and ballast, ties, rails and fill sections. service roads. Standard width. B. Foreslope To safely support track and road subgrade. To place subgrade at safe height above maximum design drainage levels. Standard width. C. Ditch To carry run-off from In all cuts. watershed served and seepage entering cut while preventing development of unstable track subgrade conditions. Width as required to accomodate hydraulics. Profile may need to be different than track profile in long level cuts. D. Backslope Resultant excavation face located between outer ditch line and natural ground line. Variable width depending on slope, height of cut face, soil stability, maintenance and erodibility. Throughout cut and fill sections. In all cuts. E. Interceptor Ditches To carry runoff from the Above cut slope. watershed served and prevent surface runoff from entering the cut. b. Width as required to accommodate hydraulics. Cut Section Design Requirements: The track roadbed (top of subgrade) portion of a cut should remain stable during the excavation and track laying operations, and once the railroad line has been placed into operation. Cut section design issues also include providing back slopes and foreslopes that will not fail. Drainage ditches need to be sized to accommodate surface runoff and subsurface water which may seep from the backslope face. Ditches made within rock cuts may need to be designed having additional width for catchment of rock materials which may fall from the backslope face. Primary consideration when designing this catchment width is to position the toe of slope at a point that will not allow falling rock fragments to bounce into the track area. The working width required by ditch cleaning machines is important. The materials that will be encountered in the cut must be evaluated for excavatability. Cuts may need to be designed with flat slopes to facilitate self-cleaning by prevailing winds and minimize snow storage. Benching of the backslope may be required to accommodate drainage and to catch falling rocks. 1.2.2.2 Back Slopes in Cuts Slope stability analysis should be performed to aid in selecting the steepest safe backslope section. Cross-sections should then be drawn transverse to the proposed track alignment to determine if safe cuts can be made within the right-of-way lines or if additional right-of-way or soil slope reinforcement will be required for the project. Soils and rock materials having varying strengths may necessitate that the backslope be cut at varying slopes. Subsurface water that seeps from the face of the backslopes can facilitate embankment instability. Vertical interceptor drains and horizontal drains may need to be designed into the backslope to intercept subsurface groundwater flow and reduce hydrostatic pressures which could cause embankment instability. 1.2.2.3 Drainage Ditches in Cuts Ditches designed for drainage and catchment (as shown in Figure 1-1-2) should be designed to have the capacity to handle regional surface water runoff, snow storage and talus. The capacity is influenced by the width, depth and gradient of the ditch. Reference should be made to Article 1.2.4 which provides specific ditch design guidelines. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-14 AREMA Manual for Railway Engineering Roadbed 1.2.2.4 Track Bed Performance in Cuts Track performance is enhanced by providing uniform stable subgrade conditions through out a given cut. Providing drainage of the immediate subgrade materials generally improves subgrade stability by increasing the materials strength while reducing the detrimental effects of frost action. Longitudinal and transverse drains can be designed to facilitate subgrade drainage. 1.2.2.5 Cuts in Soil 1.2.2.5.1 General a. Considerations such as the proposed slope angle, drainage conditions, and moisture conditions and strength of the soils encountered in a cut are the most significant factors that influence the stability of earth slopes. All sloping soils have a tendency to move under the influence of gravity. Slope stability evaluations should generally be made to select the cross-section for cuts over 15 feet deep. Observations of nearby cuts in similar soils and natural slopes in the project locale can aid in slope design. b. It is important that the cut cross-section be wide enough to provide side ditches for interception of surface water. Where it is not practical to collect surface drainage with adequate ditches, buried drainage pipes can be provided. It may be very important to relieve subsurface water pressure in sloping ground to avoid slope failures. The subsurface water pressure may be reduced by installing interceptor ditches or drains above the slope, or horizontal buried drainage pipes at critical depths within the slope either longitudinal or transverse to the cut face. In rare cases, vertical wells may be required. 1.2.2.5.2 Cuts in Cohesionless Soils (Sands and Gravels) a. Sands and gravels that are located above the ground water level generally will stand safely at a slope 2(H):1(V) or flatter. Steeper slopes may be able to be excavated and stand for short periods of time, but will eventually try to assume a flatter slope. Finished slopes in sand-gravel materials that are exposed to groundwater flow or seepage from the backslope face will routinely have to be cut flatter than would be required for the same cohesionless soil cut in a non-saturated state. In areas of loose saturated cohesionless soils, special provisions may be required to avoid liquefaction. b. The stability of slopes in sand is generally improved as the density of the cohesionless soil increases. 1 3 1.2.2.5.3 Cuts in Cohesive Soils (Silts and Clays) a. Cuts in cohesive soils need to be designed with caution. Previously stable slopes have been known to fail. Cuts in cohesive soils should be designed using slope stability analysis. Local long-term experience may prove to be an indicator of a stable slope for a particular soil profile. A slope of 2(H):1(V) or flatter generally proves stable in cohesive soils. Clay slopes over 10 to 15 feet in height should be designed on the basis of laboratory tests and slope stability analysis. In general, the higher the cut section becomes the flatter the slope will have to be to remain stable. Highly plastic clay soils require flatter slopes than those discussed above. b. The stability of clay slopes can be increased by the installation of drains and by flattening the cut slope. c. Cut slopes in areas where it is known that slides are inevitable may be designed to allow for slope movement (failure) without interference to traffic. 1.2.2.5.4 Cuts in Non-Uniform Soils Cuts in soils which are layered or contain seams of varied soil types should be designed on the basis of a slope stability analysis. The seams that contain cohesionless (granular) soils are often water bearing during some part of the year and drainage of these seams should be provided. Effective drainage may stabilize an otherwise unstable slope if the soil properties of the unsaturated (drained) embankment soils are adequate. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-15 4 Roadway and Ballast 1.2.2.5.5 Cuts in Loess In site specific cases cuts in loess can be designed with near-vertical or flatter slopes based upon the engineering properties of the soils and the findings of slope stability analysis. Cuts in loess that are designed to have a nearvertical face should be carefully drained at the foot and top of the face. Loess soils possess a natural cementation that is soluble, a uniform grading, and a vertical root hole structure. Deep cuts can be made with near vertical faces and berms, but it is critical to the stability of the backslope that drainage be carefully designed and maintained so that water does not accumulate atop the benches. 1.2.2.5.6 Cut Slope Summary For every soil type it is necessary to maintain a safe and stable cut section. This should be the primary consideration during design. Berms, drainage, erosion protection, filter layers, vegetation and proper selection of the finished cut slope angle should be used as a means of achieving this end. Discussion is provided in Article 1.4.3 and Article 1.4.5. Cribs or retaining walls may be used in troublesome sections where berms and other less costly means of providing a stable cut slope are unable to be installed. Details for the design of crib and retaining walls are given in Chapter 8, Concrete Structures and Foundations. While slope control structures and techniques add to costs, they will pay dividends in reduced requirements for slope restoration and ditch cleaning. 1.2.2.6 Cuts in Rock 1.2.2.6.1 General The design of a rock cut is predicated on obtaining the lowest balanced construction and maintenance cost consistent with safety. The ratio between construction and maintenance costs will vary with individual situations and should be developed for each project. 1.2.2.6.2 Assembly of Design Information a. Factors which should be evaluated when designing rock cuts are the 3-dimensional competence of the rock and overburden, and the depth and length of the cut. b. The first steps in design are the preparation of profiles and cross sections on which are plotted data obtained during site investigation, test borings and laboratory testing, interpreted with the aid of geological maps, groundwater surveys and aerial photographs. Knowledge of the behavior of similar rock in comparable cuts can prove to be valuable design information. c. In layered formations, where dip or strike of the bedding planes is not normal to the center of the cut, it may be desirable to evaluate sections on the dip of the bedding planes to aid in examining the stability of the cut slope. d. As the characteristics of bedrock often vary greatly (over short distances) it is fundamental for economy that the slope be fitted to the material and exposure on each side of the cut at each location. A uniform slope in one segment of rock is not necessarily appropriate throughout the length of a cut if the condition of the rock (i.e., strike and dip of bedding planes, fracturing, etc.) changes. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-16 AREMA Manual for Railway Engineering Roadbed 1.2.2.6.3 Width of Base of Cut in Rock The base width of a rock cut is determined by the total width of zones A, B, and C, shown in Figure 1-1-2 and described in Table 1-1-7. Refer also to Article 1.2.2.6.7. Figure 1-1-2. Width of Rock Cut Base 1 Table 1-1-7. Factors Affecting Base Width of Rock Cuts SEGMENT PURPOSE WHERE PROVIDED WIDTH & PROFILE 3 A. Roadbed To provide base for supporting ballast, ties and rail. Throughout cut. Standard width. B. Drainage Ditch To carry run-off from watershed served, seepage entering cut, and for service road. Throughout cut. Standard width with profile that may have to be steeper than track profile in long level cuts. C. Catchment Ditch To contain material Within broken or (Optional) which may fall from rapidly weakening faces of cut, and for rocks cuts. service and maintenance access. Of variable width depending on slope and height of cut face, size and rate of fall fragments and desirable frequency of ditch cleaning. Primary consideration in setting width is to position the toe of slope at a point which will not allow falling fragments to bounce into track area. Working width required by ditch cleaning machines is important. 1.2.2.6.4 Stability of Rock Slopes a. Safe slopes are governed by the characteristics of the rock in the slope. Slope angles should be chosen independently even in the same cut for sound rock, weathered or shattered rock, and overburden. See Figure 1-1-3, Figure 1-1-4, Figure 1-1-5 and Figure 1-1-6. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-17 4 Roadway and Ballast b. For each rock material the slope is governed to a major degree by bedding planes, joints which are usually perpendicular to the bedding, fracture patterns and faulting, all of which tend to make the rock perform as a number of segments rather than as a mass. The influence of each of these characteristics should be carefully assessed in analyzing slope stability. It should be noted that the slope of such discontinuities, as entered on cross-sections, and profiles will not necessarily show their true angle of interception with the cut slope, which should be considered in design. c. Stability of rock slopes can be analyzed using 3-D slope stability analysis with use of a stereo net software program, or by the method of slices (when appropriate) as used with soil slopes, but it should be realized that the surface of sliding will follow rock joints and defects where possible. Values of shear strength (friction angle and cohesion) are chosen accordingly. Cohesion is usually neglected as its value along joints in rock may be small. Experience is needed to design major slopes with safety and economy. d. Design factors for the more common rock conditions are discussed in Table 1-1-8. The effects of water (hydrostatic) pressure in fissures is of primary importance in all cases. e. Rock falls and slides commonly occur during or soon after heavy rains, which is an indicator of the major importance of seepage pressures on slope stability. Water has the dual effect of increasing shear stresses in the slope by its weight and hydrostatic pressure, and at the same time decreasing the shear strength of rock materials by weathering, freezing and expansion. Hence, it is important to keep water out of the slope if possible. Figure 1-1-3. Variable Slope © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-18 AREMA Manual for Railway Engineering Roadbed 1 3 Figure 1-1-4. Uniform Slope 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-19 Roadway and Ballast Figure 1-1-5. Permanent Bench Figure 1-1-6. Temporary Bench © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-20 AREMA Manual for Railway Engineering Roadbed Table 1-1-8. Design Factors for Rock Slopes Condition of Rock Design of Slope Hard rock with random joints Providing there are no adverse bedding planes or joint systems, ground water pressures are low and blasting is presplit, slopes of 70 degrees are stable. Layered rock An accurate joint survey is important. If rock dips with the slope, and dip angle is greater than angle of friction, critical slope is at angle of dip. If bedding is horizontal, stability is as for massive rock. If bedding dips into slope, critical slope is between 70 degrees and 90 degrees; local rock falls may be frequent. Fractured or weathered rocks Stability can be analyzed using shear strength parameters derived from field observations. Angle of friction for angular crushed rock varies between 45-50 degrees. Clay-shale rocks Specialist advice is required as unloaded shale tends to decrease in strength with time. f. In most rock masses, the ground water table cannot be lowered economically. However, intercepting surface ditches at the top of the slope or horizontal relief drains in the face or at the toe of the slope may have benefits in certain cases (see Section 1.4, Maintenance). 1.2.2.6.5 Effect of Blasting Uncontrolled blasting tends to open up cracks near the face of rock slopes, allowing an increase in the rate of weathering, infiltration of water and consequent deterioration of the slope. Such blasting may facilitate excessive rock falls for many years. A decision on the type of blasting should be part of the design procedure. The technique of pre-splitting by blasting a line of drill holes on centers less than 4 feet apart can produce a slope surface with minimum disturbance and negligible overbreak. Preservation of the rock segments in their pre-construction position allows valid design assumptions to be made and minimizes ultimate maintenance costs. 1 1.2.2.6.6 Use of Benches on Rock Slopes a. Benches in rock cuts are used to catch falling rock, to prevent undermining of hard strata by differential weathering, to reduce pressures at the toe of cuts and to handle drainage. Principles applying to the choice of rock slopes and benches are illustrated in Figure 1-1-3, Figure 1-1-4, Figure 1-1-5, and Figure 1-1-6. Where permanent benches are used to intercept falling rock, as shown in Figure 1-1-5, access should be provided for periodic removal of debris. The width of such benches should be adequate for machine access after weathering of the softer rock has taken place. A minimum width of 20 to 30 feet may be required. b. In shales and other soft-rock cuts, temporary benches may be designed to contain all debris from a steep slope. c. A typical arrangement is shown in Figure 1-1-6. Debris from the top of the steep slope accumulates on the bench to form a protective zone for the toe of the slope, while the upper portion of the steep slope weathers back to its angle of repose. Provision for access to such slopes may not be required. d. Benches used to reduce the effects of differential weathering are located at the top of the weaker rock where the stronger rock is set back to form the bench. The width of the bench is governed by the weathering characteristics of the weaker rock and the height and angle of its slope. Provision for access may not be required. e. In deep rock cuts, where weaker rock appears in the base of the cut, it may be necessary to introduce benches to relieve the toe pressure. Such benches may serve other purposes, as noted above, to increase safety and reduce maintenance costs. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-21 3 4 Roadway and Ballast f. A permanent bench may be required for accommodating longitudinal drainage from surface run-off or subsurface seepage. Such an arrangement is usually complicated and expensive and should be avoided, except in special circumstances. g. Drainage of benches is best accomplished by sloping them to the face of the cut thus moving water off the bench as quickly as possible. Where rock on the surface of the bench presents open joints or fractures, water may be prevented from entering the rock mass by covering the bench with a layer of clay or other impervious material, thus reducing or eliminating deterioration of the rock by ice wedging and erosion. 1.2.2.6.7 Catchment Ditch Design a. In rockfall zones where benches cannot be provided, design of the slopes and catchment ditches are important to prevent rock fragments from reaching the track. Falling rocks striking a slope flatter than vertical will receive a horizontal component of force tending to throw them toward the track area. For this reason, in rockfall zones the slope should be kept as nearly vertical as possible consistent with overall stability. b. Unless mature cuts in similar rock can be observed, it is difficult to predict at the design stage the manner in which rocks will fall and how fast they will accumulate at the base of the slope. Hence, ditches should be designed with ample width to collect rockfall material, keep it out of the track area and permit economical removal of debris. The cost of enlarging drainage ditches later to provide a catchment zone in rock cuts is prohibitive. c. Measures described in Article 1.4.2 on maintenance of rock slopes may be incorporated in the design stage if difficulties can be predicted. 1.2.3 FILLS (2002) 1.2.3.1 General a. Fills are used to raise the existing ground surface when required to achieve the desired level for roadbed construction. They may serve to elevate the grade above existing or predicted water levels or snow depths; to bury obstructions, undesirable topographic variations, and to achieve design grades. The two primary components that need to be considered during fill design are the embankment and the natural foundation that it is constructed on. b. Every railroad fill should be designed to satisfy the following requirements: (1) To assure the stability of the embankment under its own weight and super imposed load. (2) To assure stability of the combined embankment and foundation system. (3) To economically tolerate the magnitude of anticipated settlement. c. These design requirements are satisfied by selecting suitable soil or rock to be used for construction, controlling the placement of these materials as to location and compaction in the fill, and designing the embankment to compensate for anticipated settlement. If the fill is to serve as an impoundment structure, additional design considerations such as the permeability of the fill and its ability to withstand rapid draw down of the water level, need to be taken into consideration. d. A balance factor should be computed when calculating the quantity of required borrow material to construct an embankment fill. This balance factor is the ratio of the volume of soil from the borrow to the volume of soil placed in the fill after compaction. No standard balance factor (shrinkage factor) should be assumed. Fill materials are often compacted to a density different from their original density in the borrow. On large projects it is advisable to find cut-to-fill ratios by field density. The balance factor should be increased to compensate for soil that is lost in transport between the borrow and fill areas. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-22 AREMA Manual for Railway Engineering Roadbed 1.2.3.2 Foundations of Fills a. The foundation for a fill is required to satisfy the same basic requirements of a continuous spread foundation system. The foundation soil should have the strength to support the proposed embankment and live loads with an adequate safety factor. In addition, the fill needs to be designed and constructed (i.e., compacted and placed within a range of moisture criteria) such that it can tolerate the projected degree of settlement. It is occasionally necessary to remove and replace portions of weak or highly compressible foundation elements or to improve their characteristics by using stabilization procedures or controlled construction techniques. Controlled construction techniques could include one or combinations of the following: 1. removal and reuse in compacted fill, 2. stage construction of the fill, 3. preloading and surcharging or 4. installing subdrainage systems. b. Vegetation, topsoil and organic soils are normally removed to provide for the development of a good bond between the fill and the subsoil. The removed materials may be stockpiled for future use as topdressing in grassed areas. c. A fill underlain with “free-draining” sand or gravel will routinely have a factor of safety higher than those for cohesive silty or clayey foundation materials. The performance of computer aided slope stability analyses such as the “Modified Bishop”, “Bishop Simplified Method” or the “Janbu’s Simplified Method” should be performed to determine the stability of both the embankment and foundation components of proposed fills. A stability analysis that provides a safety factor of 1.0 implies that the driving forces that are wanting to cause a failure are equal to the resisting force in the soil and that a failure is imminent. Generally a factor of safety of 1.5 is considered adequate, although, lower safety factors may be considered acceptable if the engineer performing the stability analysis has sufficient design data available for analysis. Higher safety factors are required when limited test and field data are available for use in the performance of the slope stability analysis. d. 1 If the stability analysis indicates an adequate factor of safety for the foundation, the design will be based on the internal stability of the embankment. When the foundation is too weak to provide adequate support one or more of the following procedures could be adopted to achieve a stable fill: (1) Total or partial removal of unsuitable foundation materials, displacement of these materials, and replacement with compacted fill. 3 (2) Flattening of the slopes of the embankment section or the addition of berms at the toes of the embankment. (3) Installation of a foundation drainage system to reduce pore water pressures. (4) Stage construction of the embankment. 4 (5) Densification of sandy foundation soils. (6) Use of light embankment materials (fills). (7) Mechanical reinforcement or underpinning systems. (8) Preloading and surcharging the fill area to accelerate consolidation of clay or organic soils. e. Berms installed to improve weak foundation conditions should extend to sufficient distance beyond the failure arc to provide an adequate factor of safety to the fill. Berms should also be checked for their own stability. f. The magnitude of foundation material consolidation should be computed when embankments are built on highly compressible ground. The magnitude of settlement within the embankment section may also need to be taken into consideration when computing total settlement. The top width of the fill should be increased to compensate for the computed settlement that will occur after completion of the embankment construction. Foundation materials that consist of peat may be expected to significantly consolidate under the weight of the fill. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-23 Roadway and Ballast 1.2.3.3 Soil Fills 1.2.3.3.1 General a. A soil embankment has three basic components: a center core, shoulders or shell, and a drainage system. Homogeneous embankments use the same materials for the core and shoulders. Site conditions may not require special drainage provisions other than side ditches. When the fill functions as an earth dam or levee, the core is constructed of relatively impermeable material while the shell will generally be constructed of a material that is more permeable than the core. b. Fill slopes should be designed based on the findings of slope stability analysis. The soil properties utilized in the slope stability analysis should be determined by a geotechnical engineer using field investigation and laboratory tests. Factors that will affect the factor of safety of a fill slope are the materials used for construction, compaction of the fill material(s), stabilization berms, and the strength of the embankment materials after compaction. Fills constructed of sandy (cohesionless) materials or of cohesive materials should stand safely if constructed at slopes of 2(H):1(V), or flatter. Fills that have a sand core should be capped with cohesive or other non-erosive materials to minimize erosion of the embankment slopes. c. It is important to study the effects that a new fill will have on the drainage of water. Effective drainage away from the fill will routinely improve the stability of the proposed fill section. The probable settlement of the fill should be considered when culverts are needed to transfer the flow of water from one side to the other side of the fill. Sufficient camber should be included in the culvert installation to compensate for the anticipated magnitude of settlement and to maintain positive flow through the culvert. d. The quality and ease of constructing soil fills varies widely. There are varying qualities of material available for use when constructing an embankment. Routinely the materials that are available on the project are used to construct fill for economic reasons. e. Soils that are used in the construction of fills often consist of a combination of fine grained (cohesive) and coarse grained (cohesionless) materials. The cohesive fine grained materials consist of clays. Cohesionless materials consist of fine grained silts; and coarse grained sands, gravels, cobbles and boulders. f. Cohesionless soils generally have a higher friction angle than cohesive soils, are best compacted using vibratory equipment, are free draining, and have greater strength at higher densities. Moisture routinely facilitates compaction. Relative density tests are the most appropriate means for defining the degree of compaction for clean free-draining cohesionless materials. g. Cohesive (fine grained) soils generally consist of a combination of silts and clays. Some of the physical properties of fine grained soils include: (1) Soil moisture content influences compaction (2) Greater degree of compaction increases the soil’s strength (3) Saturation reduces the strength of the soil (4) The friction angle and cohesion of the soil are the two parameters that describe the soils strength (5) They are frost susceptible (6) Compaction is best attained using sheepsfoot rollers and impact hammers (7) The clay fraction of cohesive soils may exemplify swell characteristics © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-24 AREMA Manual for Railway Engineering Roadbed h. Fills that consist of cohesionless and cohesive soils have properties that are a combination of those that occur for each of the two separate materials. In general, the level of compaction is influenced by the composite soils moisture content. Non-free draining materials have moderate to low permeability. They have the potential for creating high quality fills due to high cohesion and friction angle characteristics. This fill material is more susceptible to frost action than purely cohesionless soils. Sheepsfoot and impact equipment are the most appropriate means of achieving compaction. These materials exemplify low to moderate swell potential depending on the clay fraction in the soil. i. The ability of various soil types to resist erosion on slopes is shown in Column 7 of Table 1-1-10. The stability of soil types in rolled fills and their compaction characteristics are shown in Columns 10 and 11 of the same Table. Methods of improving soils for use in fills are reviewed in Paragraph k below. j. The source of suitable soils is a primary factor in fill projects. Excavation, transportation and placement costs govern the final choice. Fill may be obtained from adjacent cuts, borrow areas or commercial suppliers. k. Improving the behavior of soil fills for any engineering purpose by methods which alter or control the properties of the soil is generally termed soil stabilization. There are many procedures for creating more desirable soil properties in soils, but each has limitations depending on the soil type. A stabilization method should be suitable for the soil, have the required durability, provide the necessary performance economically and be practical to the site. Table 1-1-9 presents some of the more common methods available for improving the performance of fill materials. 1 Table 1-1-9. Improvement of Soils Improvement by Densification Methods 3 Procedure Compaction Rolling or vibrating of fill in layers with moisture control. Other Methods* Vibration in depth (Vibrofloation – patented method) Compaction piles, blasting, dynamic compaction, compaction grouting, geo-piers. Drainage Gravity Pumping Consolidation* Transpiration Gravity removal of water using surface and subsurface drains. Mechanical removal of water. Surcharge loading with drainage. Planting or seeding with vegetation. Modification Blending* Cement, lime, bitumen or calcium chloride* Adding select soil, mixing, compacting. Adding to soil in small quantities, mixing with moisture control, compacting, curing. *Method requires specialist advice. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-25 4 Roadway and Ballast 1.2.3.3.2 Sidehill Fills a. The design and construction of a sidehill fill involves analyzing the stability of the natural slopes both uphill and downhill from the embankment fill. The stability of these slopes and of the fill should be analyzed separately and as a unit. b. Construction procedures should be provided to prevent the fill from sliding on the original slope. The existing slope should be properly stripped of vegetation, stepped or notched into the hillside, scarified, and compacted. The finished surface of the compacted fill should be allowed to remain slightly roughened to facilitate bonding with subsequent lifts of fill. Drainage should be provided to intercept surface water runoff on the uphill side of the fill and, thereby, prevent it from seeping along the fill-slope interface. Erosion protection for the slopes may be necessary, as detailed in Article 1.4.5, Drainage and Erosion Control (2007) below. c. The safety of fills constructed on sidehill slopes can be improved by increasing the size of the drainage ditch on the uphill toe of slope and providing bonding benches and toe benches. The fill and its loads combine to reduce the stability of the original slope. Care should be exercised to assure that excavations do not remove material below the toe of the fill on the downhill side of the fill or that construction does not place a surcharge on or above the uphill slope which will increase the moving forces. 1.2.3.4 Rock Fills 1.2.3.4.1 General a. Article 1.2.3.1 and Article 1.2.3.2 apply to rock fills as well as earthen cohesive and cohesionless soils. As with earth fills, rock fills by economic necessity are composed of materials available from project cuts except in unusual circumstances where the rock is of a nature that it will not support the loads placed upon it or some other unacceptable condition exists. b. One such condition is the tendency of some rock fills to be subject to long term settlement due to the gradual compaction of the embankment fill itself. Where long-term settlement cannot be tolerated, the use of select borrow or a bridge or trestle may be required. Rock fills, however, are successfully used for railway installations where settlement may be easily corrected by periodic track lifting. Many rock fills over 100 feet high have been successfully constructed and maintained. Geotechnical engineers who have knowledge of rock fill construction should develop the construction details where very high fills appear economically feasible. 1.2.3.4.2 Soft Rock Fills a. By definition herein, “soft rock” refers to rock which may be excavated by power machinery without blasting or to rock which weathers rapidly upon exposure, even though blasting may have been required for its initial removal. b. Soft rock may result in an impervious fill and therefore should be located within the fill at such locations that will allow for proper drainage and maintain embankment stability. Soft rock fill materials are sometimes treated as earth/soil materials when assigning strength characteristics and compaction requirements. Slope design is best based on laboratory test results, with due regard given to possible softening of the soft rock with aging and observation of performance of similar fills constructed in the past. The suggested steepest slope for fills up to 30 feet high are 2(H):1(V) or flatter for impervious soft rock. A geotechnical engineer should analyze and design fill sections constructed of soft rock. 1.2.3.4.3 Hard Rock Fills a. Hard rock requires blasting for removal and is sufficiently weather-resistant to retain its strength after long exposure to elements. Fills containing only hard rock are usually resistant to slides and are otherwise stable except that such fills often contain a high percentage of voids which cause long-term settlements. Recommended slopes are 1.5(H):1(V) or flatter for fills up to 50 feet high, and 2(H):1(V) or flatter for higher fills constructed of hard rock. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-26 AREMA Manual for Railway Engineering Roadbed b. The percentage of voids and hence the settlement of a rock fill may be reduced by limiting the depth of each layer placed during construction, mixing soft rock or soil with the hard rock, compacting the fill in place, or any combination of these methods. Layers 24 to 30 inches deep are recommended with the maximum individual rock size not exceeding the layer thickness. Heavy-duty, rubber-tired rollers (50 tons or heavier) have been used to compact well-graded broken rock to 83 to 88% of its unit weight in the solid state. 1.2.3.4.4 Zoning of Rock a. When both hard and soft rock are available to construct a fill, it is recommended that each material be located in such a position as to take advantage of and preserve its strength, reduce or eliminate slope erosion, provide necessary drainage and avoid trapping of water within the fill. b. Figure 1-1-7 shows a cross-section of a fill where the softer, weaker and less pervious rock is located in the core of the fill. The outer slope of the fill is determined by the slope needed for the weaker core material. By enveloping the core with the hard rock, the resulting slopes are strengthened, drainage is provided and the strength of the weaker rock materials is maintained by keeping its surface from the weather. Settlement is also reduced because the softer core material may be compacted to a density more nearly to that which existed in its natural state. 1 3 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-27 Roadway and Ballast Figure 1-1-7. Zoning of Rock Fill Materials c. Other zoning arrangements may be made, such as protecting a soft-rock core with clay soil, placing hard and soft materials in alternate layers, and mixing hard and soft materials to reduce settlement. REFERENCES (1) Duncan, C. Wyllie; Foundations On Rock; Chapman & Hall, London; 1992. (2) American Society of Civil Engineers; Rock Foundations – Technical Engineering & Design Guides As Adapted From The U.S. Army Corp of Engineers, No. 16; ASCE Press; 1996. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-28 AREMA Manual for Railway Engineering (2) (3) Symbol Soil Group Field Identification Gravels (1) GW Well-graded GRAVELS and well-graded GRAVELS with SAND mixtures, trace to no silt or clay GP Predominantly one size, or a Poorly-graded GRAVELS and poorly-graded GRAVEL range of sizes with some with SAND mixtures, trace missing, no dry strength to no silt or clay GM Sands © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering Table 1-1-10. Soil Groups, Their Characteristics and Uses Wide range in grain sizes, substantial amounts of all intermediate sizes, no dry strength (4) (5) (6) Value as Frost Drainage Filter Layer Heaving (7) Erosion on Exposed Slope (8) (9) (10) Stability in Value as Pumping Compacted Subgrade Action Fills (11) (12) Compaction Characteristics Typical Duty Type Geotextile Fabric Use None to Excellent very slight Fair None* Excellent None Very Good Excellent; crawlertype tractor, rubbertired roller, steelwheeled roller None required None to Excellent very slight Fair to poor None* Excellent None Reasonably good Good; crawler-type tractor, rubber-tired roller, steel-wheeled roller None required Very poor None to slight Good None Reasonably good Good with close moisture control; rubber-tired roller, sheepfoot roller None required SILTY GRAVEL and SILTY Fines with low or no plasticity, Slight to Fair to GRAVEL with sand slight to no dry strength medium very poor mixture CLAYEY GRAVEL and GC CLAYEY GRAVEL with sand mixture Plastic fines, medium to high dry strength Slight to Poor to medium very poor Not to be used None to slight Good Slight Fair Excellent; rubberNone required tired roller, sheepfoot roller Well-graded SAND and well-graded SAND with SW GRAVEL mixtures, trace to no silt or clay Wide range in grain sizes, substantial amounts of all intermediate sizes, no dry strength None to Excellent very slight Excellent Slight to high with decreasing gravel content Excellent None Very good Excellent; crawlertype tractor, rubbertired roller None required Predominantly one size, or a Poorly graded SAND and poorly graded SAND with range of sizes with some GRAVEL mixtures, trace to missing, no dry strength no silt or clay None to Excellent very slight Fair to poor High Good None Reasonably good with flat slopes Good; crawler-type tractor, rubber-tired roller None required SILTY SAND and SILTY SAND with GRAVEL mixtures Fines of low to no plasticity, slight to no dry strength Slight to Fair to high very poor Very poor High Poor None to slight Fair Good with close moisture control; rubber-tired roller, sheepfoot roller Slight regular Plastic fines, medium to high dry strength Slight to Very poor high Not to be used Slight Poor Slight Fair Excellent; rubberSlight regular tired roller, sheepfoot roller SP SM CLAYEY SAND and SC CLAYEY SAND with GRAVEL mixture Roadbed 1-1-29 Table 1-1-10. Soil Groups, Their Characteristics and Uses (Continued) (3) Symbol Soil Group Field Identification Of High Plasticity ORGANIC AREMA Manual for Railway Engineering © 2010, American Railway Engineering and Maintenance-of-Way Association Silts and Clays Of Low Plasticity (2) (4) (5) (6) Frost Value as Drainage Heaving Filter Layer (7) Erosion on Exposed Slope (8) (9) (10) Stability in Value as Pumping Compacted Subgrade Action Fills (11) (12) Compaction Characteristics Typical Duty Type Geotextile Fabric Use SILT or SILT with SAND or Fine grained, slight to no dry GRAVEL; SANDY SILT or strength SANDY SILT with ML GRAVEL; GAVELLY SILT or GRAVELLY SILT with SAND mixture Medium Fair to to very very poor high Not to be used Very high Poor Slight to Poor bad Poor to good with close control of moisture; rubbertired roller; sheepfoot roller Lean CLAY or Lean CLAY Medium to high dry strength with SAND or GRAVEL; SANDY LEAN CLAY or SANDY Lean CLAY with CL GRAVEL; GRAVELLY Leam CLAY or GRAVELLY Lean CLAY with SAND mixtures Medium Very poor to high Not to be used None to slight Bad Bad Fair to good; rubber- Yes heavy tired roller, sheepfoot roller Elastic SILT or elastic SILT Slight to medium dry strength Medium Poor to to very very poor with SAND or GRAVEL; high SANDY elastic SILT or SANDY elastic SILT with MH GRAVEL; GRAVELLY elastic SILT or GRAVELLY elastic SILT with SAND mixtures Not to be used None to slight Bad Very bad Poor Poor to very poor; sheepfoot roller Yes heavy Fat CLAY or fat CLAY with Sticky when wet, high dry SAND or GRAVEL; SANDY strength fat CLAY or SANDY fat CH CLAY with GRAVEL; GRAVELLY fat CLAY or GRAVELLY fat CLAY with SAND mixtures Medium Very poor Not to be used None Bad Very bad Fair with flat slopes Fair to poor; sheepfoot roller Yes extra heavy Organic SILT or CLAY and High smell, dark colour, with SAND or GRAVEL; mottled appearance, slight to SANDY or GRAVELLY high dry strength OH organic SILT or CLAY with GRAVEL or SAND respectively Medium Poor to to high very poor Not to be used Variable Bad Very bad Not to be used Poor to very poor Yes extra heavy Slight to Poor high Not to be used Not applicable Remove completely Very bad Not to be used Compaction not possible Yes extra heavy PT PEAT Dark colour, spongy feel and fibrous texture Reasonable Adapted from ASTM Method D 2487T NOTES: Column 2: Soil types in capitals and underlined make up more than 50% of sample. Other soil types in capitals make up more than 5%. Column 4: Tendency of soil to frost heave. Column 5: Ability of soil to drain water by gravity. Drainage ability decreases with decreasing average grain size. Column 6: Value of soil as filter backfill around subdrain pipes to prevent clogging with fines, and as filter layer to prevent migration of fines from below. Column 7: Ability of natural soil to resist erosion on an exposed slope. Soils marked * may be used to protect eroding slopes of other materials. Column 8: Value as stable subgrade for roadbed, when protected by suitable ballast and sub-ballast material. Good soils may be used to protect poorer soils in subgrade. Yes regular Roadway and Ballast 1-1-30 (1) Table 1-1-10. Soil Groups, Their Characteristics and Uses (Continued) (2) (3) Symbol Soil Group Field Identification (4) (5) (6) Frost Value as Drainage Heaving Filter Layer (7) Erosion on Exposed Slope (8) (9) (10) Stability in Value as Pumping Compacted Subgrade Action Fills (11) (12) Compaction Characteristics Typical Duty Type Geotextile Fabric Use Column 9: Tendency of soil to pump up and foul ballast under traffic. Column 10: Stability of soil against bulging and subsidence when used in a rolled fill. Cross check with Column (7) to forecast tendency to erode. Column 11: Equipment listed will usually produce the required densities with a reasonable number of passes when moisture content and thickness of lift are properly controlled. Column 12: Typical type Geotextile Fabric. Use is dependent upon existing or proposed subgrade design. Fabric will not improve soil classification. If additional strength is required, use enough stabilized material, granular base material, sub-ballast and ballast to properly span the weak subgrade soil. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering (1) Roadbed 1-1-31 Roadway and Ballast 1.2.4 DRAINAGE (2003) 1.2.4.1 General a. This section deals with the surface and subsurface drainage of the roadway as distinguished from drainage of the ground surface by natural waterways. The latter subject is dealt with in Part 3 Natural Waterways, and Part 4 Culverts. b. Since water is the principal influence on soil stability in roadbed, subgrade and slopes, control of surface and subsurface water is the most important factor in roadway design and maintenance. 1.2.4.2 Surface Drainage a. Surface water from the roadway area, and sometimes surrounding topography, is usually handled by a system of ditches parallel to the roadbed with offtake ditches where necessary. The roadbed cross section, slopes of cuts and fills, ditches, catch basins, and culverts should all form a balanced system to dispose of the water without accumulation or excessive saturation which would produce damaging effects. b. The design capacity of any part of the system can be calculated if the quantity of water to be carried, the distance and grade to outfall, and the infiltration factor of the soil are known. Ditches should be deep enough and sized for handling the design runoff anticipated while allowing the subgrade to drain. Trackside ditches should be sized for the anticipated runoff and the flow velocity calculated using the Manning equation. c. The ditch grade may be governed by the track grade, particularly in long cuts or offtake drainage points. However, more often than not, ditch grades will be governed by existing drainage patterns and points of discharge. When the ditch is constructed in earth materials, the minimum recommended grade should not be less than 0.25% to minimize sedimentation. However, exceptions to this may be dictated by local topography such as in low-lying or flat terrain. Likewise, to prevent erosion, the maximum unlined ditch grade and/or ditch configuration should be such that it will produce a velocity less than or equal to the limiting velocity shown in Table 1-1-11. Erosion may also be prevented or reduced by paving, riprapping, sodding, or constructing check dams depending on velocity, type of soil, and depth of flow (see Part 3 Natural Waterways). Linings for ditches are typically classified as either rigid or flexible. Asphaltic concrete and Portland cement concrete linings are examples of rigid linings. Riprap, sod, and grass linings are examples of flexible linings. Rigid linings are better at limiting erosion and they often permit higher water velocities since they are smoother than flexible linings. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-32 AREMA Manual for Railway Engineering Roadbed Table 1-1-11. Guidelines for Limiting Velocities to Prevent Erosion Material d. e. Velocity (Ft per Sec) Sand Up to 2 Loam 2-3 Grass 2-3 Clay 3-5 Clay and gravel 4-5 Good sod, coarse gravel, cobbles, soft shale 4-6 Characteristics of flow and their effects on erosion need to be considered. Generally speaking, flow in trackside ditches may be classified as steady uniform flow provided the ditch section is relatively constant. Open channel flow is uniform when the depth of flow is the same at every section of the channel, i.e. the surface of the water is parallel to the channel. Flow in trackside ditches can be further classified as either subcritical or supercritical. Flow down gentle slopes will most likely be subcritical. Flow down steep slopes would most likely be supercritical. That is to say, when the depth of water is greater than the critical depth, it is subcritical flow, and when the depth is less than critical, it is supercritical flow. Critical flow or flow near critical depth tends to be unstable and exhibits turbulence and water surface undulations. Therefore, the slope of the channel bed which would maintain critical flow, should be avoided. Critical flow is that state of flow at which the specific energy is at a minimum for a given discharge. A hydraulic jump occurs when a transition is made from subcritical to supercritical flow. Supercritical flow should be avoided in the trackside ditch design because the higher velocity can cause scour/erosion at the downstream outlet. To limit the effects of erosion at the outlet, a form of energy dissipation may be applied in the channel. Types of energy dissipators include drop structures, roughness elements such as blocks and sills, ditch checks, etc. These decrease the chance of a hydraulic jump occurring while also decreasing the chance of erosion/scour. Ditches are commonly trapezoidal or V-shaped in section. In most cases, from a constructability standpoint, it is not economical to vary the size/shape of the ditch. Although each ditch should be designed considering soil type, hydraulics and method of construction, the minimum recommended depth is 2 feet below finished subgrade at the shoulder of the roadbed. The minimum recommended depth is expected to provide freeboard and prevent saturation and infiltration of stormwater into the sub-ballast and ballast section. Additionally, the minimum recommended bottom width for trapezoidal ditches in earth materials is 3 feet realizing that wider ditches may be easier to construct if right of way is available. Side ditches should be located so that the stability of adjacent cuts and fills will be maintained. Generally the top surface of a berm, if constructed or required between the toe of a fill and the ditch, should be sloped toward the ditch for good drainage. f. Wide ditches are desirable at the toe of slopes in cuts where sloughed material tends to accumulate. Wide ditches, in addition to providing storage space, also provide working space for equipment and subsequently allow for periodic cleaning of debris and sloughed material. g. Ditches at the top of cut slopes to intercept runoff water from the uphill slope are often useful in reducing slope erosion, sloughing, or in preventing the deterioration of a rock slope due to ice formation in cracks of the rock. Intercepting ditches also reduce the quantity of water to be handled by trackside ditches. The same care should be taken in designing intercepting ditches as side ditches so that they do not create serious erosion problems. Seepage water occurring on the face of a slope may be intercepted and conducted away on benches. Benches used for drainage should be sloped back from the face and thence laterally, and should be lined if necessary to prevent infiltration. h. In low-lying or flat terrain, it may be necessary to dig offtake or adjacent ditches away from the roadway for a considerable distance to provide sufficient difference in elevation to produce drainage. In such locations, sedimentation may occur requiring periodic cleaning of ditches. An alternate would be to provide catchment areas outside the embankment area for accumulation and evaporation of runoff if right of way is available. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-33 1 3 4 Roadway and Ballast REFERENCES (1) H.W. King, E.F. Brater, J.W. Lindell and C.Y. Wei, Handbook of Hydraulics, McGraw-Hill, New York 7th Edition, 1996. (2) Ven Te Chow, Ph.D., Open Channel Hydraulics, McGraw-Hill Book Company, New York, 1959, Reissued 1988. (3) F.S. Merritt, M.K. Loftin and J.T. Ricketts, Standard Handbook for Civil Engineers, McGraw-Hill, New York, 4th Edition, 1996. 1.2.4.3 Subsurface Drainage 1.2.4.3.1 Importance a. Only a portion of rainwater is handled by natural and man-made watercourses. The remaining water infiltrates the soil and becomes either ground water or capillary water. Where ground water is high, subsurface drainage may be needed to draw the water table down so that softening of the subgrade soils, sloughing, or instability of slopes will not occur. Capillary water cannot be removed by drainage but can sometimes be controlled by lowering the water table. Lowering the water table will assist in reducing the amount of heaving track caused by frost, reduce the pumping and infiltration of soil into the sub-ballast and ballast sections, and reduce the potential for developing ballast pockets. b. The suitability of various soil types to gravity drainage is given in Column 5 of Table 1-1-10. 1.2.4.3.2 Definition and Function of Subdrains a. A subdrain is any covered/sealed drain below the ground surface receiving water along its length through perforations, porous walls, or joints placed in a trench backfilled with filter material. b. A subdrain may consist of a trench filled with clean, granular or crushed rock material, whereby water is intended to pass through the interstices of the material instead of a pipe, typically referred to as a French drain. Subdrains of this type frequently plug with fines from the adjacent ground unless protected by adequate filters such as a non-woven geotextile fabric. When utilizing this technique extreme care should be taken to provide for the proper design and installation. When installed properly, French drains are very effective in permitting subgrades to drain and thereby further stabilizing them. c. A subdrain may consist of a trench with perforated pipe and geotextile fabric filled with clean, granular or crushed rock material whereby water is intended to pass through the interstices of the rock material through the perforations in the pipe and out through the pipe. The perforated pipe should be laid such that the perforations are pointing down to the bottom of the trench. d. Subdrains may serve as cross drains or side drains. Cross drains are laid under the roadbed or other areas to prevent water from gathering and provide a path for water to drain out of the substructure such as the sub-ballast and subgrade. They are placed below the level of water accumulation and connected to a side drain. Cross drains typically flow into a side drain unless they are directly connected to a roadside ditch or the side of an embankment for discharge. Side drains are built to collect water from cross drains and to intercept water flowing toward the roadbed, or collect water out of the substructure. An attempt should be made to place side drains at the lowest part of seepage zones so as to collect as much of the flow of ground water as possible. 1.2.4.3.3 Design a. Subdrainage pipe is available in perforated corrugated metal, rigid plastic, bituminized fiber, and perforated or porous concrete. Part 4 Culverts, gives specifications for metal and concrete piping and methods of installation. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-34 AREMA Manual for Railway Engineering Roadbed b. Subdrainage pipe is available in diameters ranging from 2 to 24 inches. Where periodic cleaning of subdrains is required, 6 inch pipe or larger is recommended. For pipe laid at a proper gradient and surrounded with a proper filter material such cleaning should not be required. However, provisions for clean out should be made as discussed in Paragragh d. below. c. The design of subdrainage installations is made from knowledge of the depth, flow quantity, direction of flow, and seasonal fluctuations of the ground water table. Such information is best obtained by observing the soil deposits and water levels in test pits during the wet season. The location, depth, and size of pipe, French drains, and filter material are chosen accordingly. Subsurface drainage should be considered an integral part of the entire drainage system and not just an isolated, separate component. d. In normal subdrainage, approximately 300 feet of 6 inch intercepting drain may be used before a change to a larger size is necessary. Manholes/clean outs are usually installed at the same intervals. e. A slope to ensure a velocity of 2 feet per second should be used for pipe. It is important to locate the outlet where it can be maintained free from any manner of clogging or backwater. REFERENCES (1) American Iron and Steel Institute, Handbook of Steel Drainage and Highway Construction Products, Fifth Edition, 1994. (2) Concrete Pipe Design Manual, American Concrete Pipe Association, Irving, Texas. 1 (3) Uni-Bell Handbook of PVC Pipe, Third Edition, 1991, Dallas, Texas. 1.2.4.3.4 Uses Typical uses of subdrainage installations can be illustrated by the following examples. More details are found in the references. • Sidehill Seepage Under Track. Figure 1-1-8 shows a condition where a seepage zone tends to cause subgrade softening. After investigation by auger borings or test pits, the seepage is intercepted before it enters the roadbed area by a side drain, placed at a depth so that the affect of ground water is no longer significant. • Wet Cuts. Figure 1-1-9 shows a condition where track maintenance is required due to the saturated condition of the subgrade. In addition to a substantial thickness of sub-ballast, intercepting subdrains installed as shown on either side of track are necessary to stabilize the subgrade. • Cut to Fill Transitions. Figure 1-1-10 and Figure 1-1-11 show applications of subdrains at cut to fill transitions. At such locations, the flow of ground water from a cut is often interrupted by cross-sloping impervious layers, causing wet conditions and soft subgrades. A cross drain placed at this transition may intercept the seepage, and the local use of a sub-ballast thickness greater than normal will ensure a stable subgrade. • Yard and Station Areas. Unless the subgrade soil is free-draining, a system of subdrainage is advisable in yard and station areas, usually combined with a storm drainage system. Longitudinal subdrains between pairs of tracks with cross drains at 200- to 300-foot intervals will normally be satisfactory. Depth and spacing will depend on soil and ground water conditions. • Other Uses. Subdrains have also proven of benefit at road crossings, rail crossings, and behind bridge abutments. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-35 3 4 Roadway and Ballast Figure 1-1-8. Interception of Sidehill Seepage by Subdrainage Figure 1-1-9. Lowering of Ground Water In a Wet Cut © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-36 AREMA Manual for Railway Engineering Roadbed Figure 1-1-10. Lowering of Ground Water in Cut to Fill Transition (Longitudinal) 1 3 4 Figure 1-1-11. Lowering of Ground Water in Cut to Fill Transition (Sidehill) © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-37 Roadway and Ballast SECTION 1.3 CONSTRUCTION 1.3.1 GENERAL (2005) a. Construction should only occur after an engineering investigation and design have taken place and the results of these activities have been packaged in the contract documents. These documents are prepared so that the railroad or more typically, a Contractor can accomplish the project scope. Associated engineering activities should be appropriate to the size and scope of the planned project. Section 1.3 consists of general recommendations for new roadbed construction to include the initial survey, preparation of plans, and the preparation of specifications for such items as clearing and grubbing, excavation and grading, erosion and sediment control, placement of sub-ballast material, and final surface erosion control. b. An important distinction should be made between completely new railroad roadways designed and constructed separate from existing operating tracks and facilities, and railroad roadbeds constructed immediately adjacent to or beneath an operating railroad. The design approach and construction methodology for railroad roadbeds may have significant differences for new roadbeds on a new alignment versus roadbeds adjacent or beneath existing operating railroad. In instances where work is to be performed in the vicinity of active railroad operations special safety considerations are warranted. A flagman or other appropriate method should be used to protect equipment and personnel working within the fouling limit of the track or as authorized by the operating railroad of the active track. All employees working in this area must receive Roadway Worker Protection as specified by the operating railroad and FRA requirements. c. It should be recognized that in rare instances projects arise that do not allow for a traditional engineering analysis to be followed by the preparation of design documents. In these cases, the railroad or Owner should employ technical professionals that can be involved in the expedited design process as well as throughout the construction process to address site-specific issues, which would affect the performance of the new roadbed. 1.3.2 CONTRACT DOCUMENTS (2005) The preparation of Contract Documents is typically the deliverable product of the Design process. Contract documents should include, but are not limited to: drawings/plans, technical specifications, the results of specialized testing, the Owner’s contractual terms and conditions, and other pertinent project information. The owning railroad or rail client usually has established guidelines as to the type and order of precedence of the specified contents for the Contract Documents. Although the Contract Documents should fully define the proposed project, it is advisable that all parties be required to visit the site, attend pre-bid meetings when held, and become familiar with the project site conditions prior to submitting proposals to perform the work. The purpose for these site inspections is to afford all parties the opportunity to view and assess site conditions that might have an impact on construction. Examples of these conditions may include physical site constraints, access limitations, obstructions, the location and number of utilities, material disposal requirements, etc. In some instances, the Railroad may have its own detailed set of standard Contract Documents, in which case the site specific provisions need to be included. In other cases it may be more appropriate to use provisions from applicable local or regional standard specifications, such as State Departments of Transportation, or County Public Works Departments. Contract Documents are typically made up of a number of sections. Sections that are most often included are: a. Contract Drawings: The drawings are the primary means of showing the known existing conditions and the extent and magnitude of the proposed project. They provide a graphical representation of the work to be performed and generally include plans and profiles, cross-sections, construction details, and may include environmental and/or geotechnical information as appropriate. b. Technical Specifications: Written text that identifies and describes the scope of work, required submittals, quality control procedures, products/materials, performance criteria, execution of work, and outlines © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-38 AREMA Manual for Railway Engineering Roadbed provisions for measurement and payment. Technical specifications may include such items as Demolition, Site Preparation, Earthwork, Dewatering, Slope Protection, Drainage Systems, Site Utilities, Paving, and Seeding and Mulching. c. Contract Terms and Conditions: This text defines the contractual obligations of all parties. Included in this section are such things as safety requirements, insurance requirements, bonding, project schedule, track occupancy issues, coordination with railroad forces, and project payments. Contract Terms and Conditions are generally specific to the project and the Owner’s legal requirements, and will not be discussed in further detail in this section. d. Other pertinent information usually contained in the contract documents may include such things as geotechnical reports, environmental reports, drainage reports, utility agreements, and copies of permits obtained by Owner and/or requirements for permits to be obtained by the Contractor. 1.3.2.1 Plans Project plans typically include, but are not limited to, the following elements: a. Detailed plan and profile drawings show the project location, identify any affected real estate, and show significant features of the area under consideration. Profiles should show existing ground elevations and the elevations and grades of new construction within the limits of the project. Also shown in plan are such things as highway crossings, existing and new track, existing and new drainage structures, pipelines and utilities, location and water level of bodies of water and streams along the right-of-way, vegetation location and type, and other information of use to the Engineer in estimating and planning the work and to the Contractor in understanding and bidding the work. b. Soil and rock conditions may be shown. The presence of rock or soil strata may be shown on the profile sheets but are more commonly represented by boring logs given in a geotechnical section of the project drawings. This geotechnical information should be copied or reproduced in it’s entirety from the report of the Geotechnical Engineer. It should be noted that subsurface information shown on the profile between test pits or boreholes has been interpolated and may not conform to actual field conditions. It should be made clear that this information is provided for information only and the Contractor is responsible for interpretation of the information provided. c. Cross sections are typically cut at right angles to the centerline of construction. Typical cross sections for cuts and fills should be provided for the length of the project at some specified interval, which provides representation of the work to be performed and amount of materials to be excavated or filled. Cross sections should show the existing ground surface and the design cuts and fills required. Fill sections should show the type and thickness of fill materials to be placed. Drainage should be shown for both cut and fill sections. Culvert details should be shown as well as details of berms or benches, slope keying, slope drainage and blanketing, erosion protection, and any stabilization measures known to be required to produce a satisfactory design. 1.3.2.2 Technical Specifications The following section provides guideline recommendations for the major areas of work for roadbed related construction activities. These specifications are not intended to be all-inclusive for a particular project, but serve rather as a starting point for the development of project specific technical requirements. 1.3.2.3 General Conditions and Construction Engineering Control It is recommended that the projects technical specifications include a section specifically covering the general requirements for performance of work, and the means by which construction engineering and monitoring will be performed. Such a section clearly defines the responsibilities of both the Owner and Contractor regarding all aspects of project engineering, administration, and construction management. Clear definition of the requirements and the assignment of cost for each item are critical to project success. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-39 1 3 4 Roadway and Ballast 1.3.2.3.1 General Conditions Items which should be considered for inclusion in "General Conditions" include: • Safety of employees, public and railroad operations, including; Federal Railway Administration’s Roadway Worker Protection program, Personal Protective Equipment requirements, and a clearly defined policy on drug and alcohol possession or use by project personnel. • Project specific regulations regarding allowable work hours, track curfews, and/or other railway imposed limitations on construction. • Project specific environmental restrictions, such as waste disposal, construction noise, airborne particulate release, lighting, and vibration. • Contractor’s responsibility for compliance with project specific environmental permits. • Contractor’s responsibility to contact the applicable "Call Before You Dig" agency, and to comply with all notification and permit requirements. • Security of construction site including labor, material and equipment. • Field Offices, including all required utility installations, necessary office equipment, and administrative staffing requirements. • Requirements for acceptance/unloading of railroad furnished material. • Responsibility for preparing and updating Project schedule. • Requirements for daily reporting and documentation. • Inspection procedures. • Provisions for ingress, egress and other use of work site or areas adjacent to work site. Performance of General Condition items are normally considered incidental to the project and are not paid for separately. 1.3.2.3.2 Surveying The initial survey work, during the design phase, should establish horizontal and vertical control points for the project. These control points should be preserved until construction is completed. Disturbance of survey points by construction activities may result in the need to re-establish those points. Responsibility for this work should be clearly defined in the contract documents. In addition to establishing the control points for the project, the following additional survey work may be needed during construction. a. Establishment of Project Boundaries: Locate all surviving bench marks, and alignment reference and stakes from the design survey activities as noted in design plans. These should include approximate rightof-way lines, temporary or permanent bench marks previously established, or facilities (utilities, drainage structures, wells, etc.) which require special protection. b. Utility Locating: The location of existing utilities should be marked using color codes consistent with APWA or NULCA standards. c. Construction Staking: Establish centerline staking at intervals appropriate to the project. Specific staking stations would include all bridges, drainage structures, grade crossings, and utility crossings. Construction © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-40 AREMA Manual for Railway Engineering Roadbed stakes are also set to indicate cut and fill heights and the appropriate cut or fill slopes as required to establish the desired cross section. It is often necessary to reestablish the construction stakes at various times throughout the construction process. d. Permanent Instrumentation Benchmarks: In some cases, it is necessary to develop benchmarks for use in long term monitoring of a construction project. In these cases, the specific requirements for establishment of the benchmarks should be noted in the construction documents. e. As-built Surveys: At the conclusion of construction, a final as-built survey should be performed, and the project documents should be updated to indicate any changes from the original design. These documents become valuable in establishing maintenance practices and in design of future adjacent projects. 1.3.2.3.3 Construction Monitoring Construction Monitoring involves the establishment of processes and procedures for the quality control and quality assurance on the project. The individual technical specifications should establish testing requirements for each type of work. a. Quality Control: This is the regular testing of materials to verify that the requirements established in the contract documents have been achieved. b. Quality Assurance: This is the occasional document review and supplemental testing procedures, performed for the purpose of ensuring that the established quality control process is being followed and is effective. The construction documents should clearly define the responsibility and process to be followed for both quality control and quality assurance. These documents should also define how these activities are to be paid for, as well as responsibility for any remedial activities which are identified as a result of the quality control or quality assurance activities. Each technical specification should identify the quality parameters the Contractor is expected to meet and the specific test which should be used to determine when acceptable quality has been achieved. An example of a quality control process is the performance of moisture content and density tests during fill placement. In addition to portable test equipment, more permanent equipment such as standpipes, settlement gauges, and other apparatus may need to be installed to measure and observe fill performance. The Contractor should be required to facilitate such work and should avoid damaging such apparatus. Delays to his operations resulting from field tests should not be cause for claims. 1.3.2.4 Environmental Control 1 3 4 Environmental Controls are procedures and devices which are utilized to ensure that construction activity complies with applicable environmental laws and permitting requirements. Most construction activities and projects will require permits from Federal, State, Provincial and/or local agencies. Examples of these permits may include but are not limited to; Federal and or State Environmental Protection Agency, Wetland and Work in Headwaters of the US Permit (USACOE 404), National Pollution Discharge Elimination System (NPDES), Cultural Resources Affiliated Permits, Historical Preservation Associated Permits, Environmental Impact / Assessment Affiliated Permits, State Department of Natural Resources, Threatened and Endangered Species, and Federal Emergency Management Agency (FEMA) permits for work in floodways and floodplains. Certain projects may require review by the environmental analysis sections of the United States Surface Transportation Board or Transport Canada. The legal importance and potential impact to project cost and schedule of environmental permitting and environmental control installation and maintenance should not be ignored. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-41 Roadway and Ballast 1.3.2.4.1 General The Contractor should comply with all environmental control and discharge requirements set forth by applicable regulatory agencies. Proper application and implementation of Permit requirements is necessary. Typically the Owner, or its designated agent, must make application for necessary environmental permits. However, in some instances the Contractor may be required to obtain specific permits that are directly related to his operations. The United States Environmental Protection Agency (EPA) sponsors a web site with sample forms from the application process. The site is http://www.epa.gov/owm/swhb.htm. a. Erosion and Sediment Control measures to obtain or be covered by a Federal 401 Water Quality Permit should be prepared in accordance with the NPDES (National Pollution Discharge Elimination System) requirements. This includes the preparation of a SWPPP (Storm Water Pollution Prevention Plan). Typically this must be performed prior to a Contractor starting any work on the site that may disturb soil or vegetation. b. Some railroad facilities are covered by blanket permits specifically for the maintenance of facilities on existing railroad right-of-way. 1.3.2.4.2 Procedures Erosion control devices should be placed in accordance with approved permits prior to beginning clearing and grubbing, or any land disturbance activity. To perform as intended and ensure compliance with permits, devices must be properly maintained throughout the construction process. 1.3.2.4.3 Measurement and Payment a. Typically the design and permitting costs associated with Environmental Control are the responsibility of the Owner and a component of the Design Process. For some specific Environmental Control permits, the Contractor rather than the Owner may be required to apply for, obtain, and pay for, a permit. In these cases a separate pay item for this specific purpose is suggested. b. Environmental Control measures are typically measured and paid for by units of control devices installed, or paid for by lump sum. The unit or lump sum prices submitted in the proposal typically include the entire cost of furnishing all equipment, tools, materials, and labor for clearing and grubbing and disposal of materials for the areas shown on the plans. c. It is important to consider and assign responsibility for the cost of Environmental Control maintenance and/or replacement for the duration of the project. On highly complex projects, or projects of significant anticipated duration, additional measurement and payment items may be warranted to adequately protect the Owner and Contractor. 1.3.2.5 Clearing & Grubbing 1.3.2.5.1 General a. Clearing and grubbing should include the removal of items such as trees, brush, stumps, roots, all ground vegetation, unsuitable materials, embedded logs, debris, structures, foundations, etc. b. All debris resulting from the clearing and grubbing operations should be disposed of by the Contractor, in conformance with all applicable governmental regulations. c. It should be noted that timber located within the clearing limits might have value. Accordingly, contract documents should clearly define ownership and disposition of timber. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-42 AREMA Manual for Railway Engineering Roadbed 1.3.2.5.2 Procedures a. The Contractor should identify and protect existing utilities for the duration of the construction project. The Contractor should identify and protect abandoned utilities, wells, or conduits not previously identified until they may be properly retired. b. The Contractor should identify and protect established project survey control including, but not limited to, permanent and temporary benchmark monuments and property corner pins. c. Clearing and grubbing should be performed using methods that are environmentally responsible and not wasteful of earth materials required for construction purposes. d. All clearing, grubbing, and waste disposal should be done far enough in advance of other construction operations so as to not cause delay. e. Trees and other growth outside the limits specified for clearing and grubbing should be preserved and protected from damage during construction operations. f. During clearing and grubbing operations the various materials should be segregated by material type to facilitate disposal or reuse. Typical categories would include wood, rock and masonry, steel, unsuitable material, general debris, and useable soils. Special care must be given to control and properly dispose of any hazardous waste encountered during the performance of these operations. 1.3.2.5.3 Measurement and Payment a. Clearing and Grubbing is typically measured and paid for by units of one acre or fraction thereof, actually cleared and grubbed, or paid for by lump sum. The unit or lump sum prices submitted in the proposal typically include the entire cost of furnishing all equipment, tools, materials, and labor for clearing and grubbing and disposal of materials for the areas shown on the plans. b. For project sites where special or hazardous waste materials are likely to be generated during the clearing and grubbing operation, additional measurement and payment items may be warranted. For example a separate unit price for disposal by the ton or cubic yard may be used. 1 3 1.3.2.6 Grading Grading includes all earthwork operations performed as part of the construction of the railroad roadway section including the placement of granular sub-ballast materials. Work items typically include stripping, excavation, subexcavation, excavation for drainage, and placement of embankment and sub-ballast. These are specifically addressed in the following sections. 1.3.2.6.1 Stripping 1.3.2.6.1.1 General Stripping is the process of removing surface layers of vegetation, organic material, top soil, or any other materials unsuitable for use in the subgrade or foundation. If such materials can be utilized elsewhere on the project (such as for final top dressing of slopes) or are desirable for sale to outside parties, they may be segregated from other excavated materials and stockpiled. 1.3.2.6.1.2 Procedure Stripping should be performed in accordance with the project plans or as directed by the Engineer. Typically stripping should not take place until baseline excavation surveys have been performed. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-43 4 Roadway and Ballast Depth of stripping should be closely monitored to ensure that the removal depth is sufficient to address design concerns and/or variations in field conditions. 1.3.2.6.1.3 Measurement & Payment Stripping is typically measured and paid for using an in-place cubic yard basis. If stripping is a minor component of another excavation activity (such as major rock excavation) it may be considered incidental. 1.3.2.6.2 Excavation 1.3.2.6.2.1 General Excavation is the process of removing material from a work site so that the designed Cut Section and subgrade elevation are obtained. Materials to be removed are typically identified as either "Common Material (Soil)" or "Rock". In some locations "Common Material" is referred to as "Unclassified Material". 1.3.2.6.2.2 Procedures Excavation should be performed in accordance with the project plans or as directed by the Engineer. Before any excavation work is performed the appropriate "Call Before You Dig Agency" should be contacted. All excavation areas should be completed as far as is practical before borrow materials are obtained from outside sources. Weather may prevent total utilization of material from excavation areas prior to use of borrow. Borrow materials could be allowed ahead of completion of excavation only if it can be shown that all of the material from planned excavation will subsequently be utilized for embankment. Total utilization of excavation materials is important if the Contractor’s price for supplying borrow material is higher than his price for excavated material. The Contractor should maintain all working surfaces in cuts and borrow areas in a well-drained condition at all times. Surfaces should be shaped and rolled to facilitate positive drainage and minimize absorption of water. Properly drained work areas typically allow construction to resume more quickly with less waste following rainfall events. All ditches should be of the adequate length, cross-sectional area and slope to accommodate anticipated flow per the project plans, or as directed by the Engineer. All ditches should be graded to carry off water to the nearest natural watercourse with a minimum change to established drainage patterns. Waste materials or other stockpiled materials should be properly protected to avoid fouling of the channel. Care should be taken to ensure that cut slopes and subgrade sections are not undercut when excavating ditches. Ditches should be formed timely during the course of construction to promote positive drainage of the site and facilitate other construction activities. The Contractor should maintain haulage route surfaces to avoid rutting and water ponding. Ruts or depressions that are allowed to remain on the surface of the finished subgrade will cause water pockets and subgrade instability after train operations begin. The Contractor should be prepared to supply and apply water or other means of reducing dust at the excavation point or on haul roads when required by the Engineer or applicable environmental permits. 1.3.2.6.2.3 Excavation in Common Material a. "Common Material" should include all material other than "Rock" as defined herein. This should include materials such as very stiff soils, glacial till, cemented gravel, and soft and disintegrated rock which can be broken into pieces not exceeding 1 cu yd in size, by appropriate equipment, such as heavy ripping equipment that does not require blasting for removal. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-44 AREMA Manual for Railway Engineering Roadbed b. If the condition of the subgrade material in a cut is considered unsuitable by the Engineer, the material should be removed or otherwise treated as directed. Replacement with backfill should be performed with approved material that is compacted in accordance with the requirements of the project specification. The supporting strength of the subgrade in cuts must be made at least equal to that on adjacent fills. Subexcavation in cut areas and subsequent backfill with structural fill material is a common corrective measure. c. Intercepting ditches should be excavated behind the top of cut slopes prior to excavation of the adjacent cut at locations designated by the project plans or as directed by the Engineer to intercept water flowing toward excavation areas. Material generated by excavation of intercepting ditches could be used to form a berm between the intercepting ditch and the top of the cut. d. Material from any excavation, including drainage ditches, not required or not approved for use in fills should be disposed of as approved by the Engineer. e. Excess material may require spreading, sloping, compaction or other treatment to ensure the stability of the disposal area and its foundation. This is particularly important if the disposal area is located adjacent to or above track grade. f. Slide materials that develop in cuts after they are properly formed, should be removed immediately by the Contractor and the slopes should be modified, or otherwise treated as approved by the Engineer. Work required to stabilize slopes could include such measures as flattening or benching of slopes, retainage structure construction, surface or subsurface drains, and blanketing with coarse granular material. 1.3.2.6.2.4 Excavation in Rock a. "Rock" is typically all material considered as an integral part of bedrock which, in the opinion of the Engineer, is not rippable, and requires continuous mechanical impacting, drilling and/or blasting operations for removal. This definition of "Rock" may need to be adjusted to suit local conditions. Excavation of rock is typically undertaken to enable the desired alignment to be created, enhance the stability of cut slopes, and create drainage and catchment ditches. Project conditions may also require the generation of rock fill material in lieu of "Common Material" borrow. b. The Contractor should exercise care and use suitable methods when excavating to avoid breaking down, loosening or otherwise damaging rock beyond the specified subgrade level and cut slope lines. This general requirement should be replaced by particular requirements where rock strata are adversely sloping or jointed. The effect of blasting on long term slope maintenance should be considered and the appropriate type of blasting specified. c. Side slopes in rock cuts may be formed by the general method of shaping them concurrently with or after the removal of material from the cut or by the method of advance pre-splitting rock along the required plane by blasting. If, in the opinion of the Engineer, the method chosen by the Contractor is not producing acceptable forming of slopes, the Engineer may require a change in method. Rock beyond the line of the side slopes, which is loosened by blasting or overbreak caused by construction operations beyond the specified subgrade rendering it liable to slide or fall in the opinion of the Engineer should be removed by the Contractor at his expense. d. Where rock materials are required for construction of fills, the Contractor should carry out blasting in such a manner that the rock will generally meet fill requirements. e. The bottom of rock cuts should be excavated in such a manner that there will be free drainage without water pockets. Ditches in rock cuts should be drilled and blasted only after the rock cut is excavated. It is particularly important to prevent water pockets at the ends of rock cuts due to incomplete rock excavation at the junction of rock and overburden at the specified subgrade level. f. Unless otherwise specified, excavation below the subgrade level should be built up with approved structural fill material, compacted to the correct subgrade level and width for which no additional payment will be made. In frost areas it is important that material approved for back fill in rock cuts be clean granular material. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-45 1 3 4 Roadway and Ballast g. Intentional overexcavation and backfilling may be specified to remove rock subgrade material, in order to provide a uniform track subgrade modulus between cuts and fills. 1.3.2.6.2.5 Controlled Blasting of Rock a. If controlled blasting is required to progress excavation, it should be done with extreme care only by experienced and licensed Contractors in accordance with all applicable federal, state and local laws, codes, and ordinances. The Contractor must fully comply with all regulations governing the transportation, storage, handling, and use of explosives, and should be made responsible for obtaining all necessary permits. b. The Contractor should make all necessary arrangements satisfactory to the Engineer for the performance of controlled blasting within the entire area of the contract. Complete and continuous precautions should be taken by the Contractor to prevent any damages to persons, vehicles, railway equipment or track structure, aerial or buried utility lines, structures, dwellings, or other manmade installations by reason of concussion, vibration or flying material. When necessary to protect property or facilities from the mechanical effects of controlled blasting, such as heaving by displacement, or projection of debris, properly weighted blasting mats, steel cable meshes, or other approved protective devices shall be utilized. c. A detailed safety plan for the controlled blasting activities should be developed by the Contractor and approved by the Engineer. Such a plan should outline the methods and signals to be utilized by the Contractor to ensure clearance of the blast site, as well as the method to be utilized to absolutely protect rail traffic before, during, and after the controlled blasting activity. No blasting shall be performed without the presence of the Engineer or his authorized representative. d. Prior to the commencement of controlled blasting operations, the Contractor shall submit to the Engineer for approval a blasting plan, including the drilling plan, a loading plan, and the type of initiation system to be utilized. The use of electrical caps should not be allowed. Approval of the blasting plan by the Engineer shall not relieve the Contractor from liability. e. If the Engineer deems that site conditions or the blasting plan warrant seismic monitoring, an evaluation and seismic report for each shot shall be furnished to the Engineer for review. In the event the maximum peak vector established for the location is exceeded, or if unexpected results occur, the Contractor shall furnish an analysis of the affects on the surrounding conditions, i.e., structures, geology, etc., and the proposed changes to the blasting plan to correct the action, to the Engineer for review and approval before continuing blasting operations. f. When utilized to shape side slopes in cuts, advanced pre-splitting shall be performed in such manner as to produce a uniform plane of rupture in the rock, such that the resulting back slope face shall be unaffected by subsequent blasting and excavation operations within the section. The plane shall be formed for the entire depth of the cut or to a predetermined bench level. g. Controlled blasting shall be performed in such a way that rock outside the authorized excavation lines shall not be unduly loosened. If rock below the line of the side slope is loosened by advanced pre-splitting, or by the primary blast to such an extent to render it liable to slip or slide, the loosened rock shall be removed by the Contractor. Rock cuts shall be removed to a depth of 12 inches below the proposed subgrade elevation and refilled to the subgrade elevation with approved material. 1.3.2.6.2.6 Measurement & Payment The typical pay quantity for each classification, i.e. common material or rock, is the cubic yard. Payment is made only for quantities of excavation which are required for the proper completion of work items covered in this section. Additional excavation undertaken by the Contractor carelessly or solely for his benefit, such as required for haul roads, relocation of equipment, and backfilling operations, should not be included when payment quantities are measured. When excavation is considered "Cut to Fill", material is typically measured once "in place", placed and accepted, or calculated against the prepared (Cleared, Grubbed and Stripped) ground surface. Also see Placement of Embankment. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-46 AREMA Manual for Railway Engineering Roadbed When excavation is considered "Cut to Waste" material is measured by determining a volume of excavation based on an original (Cleared and Grubbed) ground surface and completed and accepted design surfaces. It is recommended that care be taken in structuring of bid documents and specifications to avoid creating a scenario where the Owners pay for excavation and then again pays for placement as embankment of the same material. 1.3.2.6.3 Subexcavation 1.3.2.6.3.1 General Subexcavation is defined as excavation that is required to remove unstable/unsuitable materials located below the project plan grade lines. The need for subexcavation may be predetermined as part of a geotechnical exploration program performed during the design phase of the project, or more routinely as an engineering decision made during construction. 1.3.2.6.3.2 Procedures Subexcavation should only be performed at the direction of the Engineer. In its simplest form, subexcavation may consist of the total removal of unsuitable materials down to stable subgrade soils and replacement with compacted earth fill. More complex forms of subexcavation may involve the excavation of a portion or all of the unsuitable subgrade soils and their replacement with stabilization materials to facilitate the subsequent construction of the embankment structure. Stabilization materials may consist of utilizing the excavated unsuitable soils and their mixing with admixtures to make them suitable embankment soils. Stabilization materials may consist of granular material possibly in combination with a geosynthetic material to facilitate subsequent grading operations. Other locally accepted stabilization techniques may be utilized with approval of the Engineer. 1 1.3.2.6.3.3 Measurement & Payment Measurement and payment may be based on a unit price compensation depending on the method of subexcavation identified in the bid document; typically measured in cubic yards. The particular method may or may not be used depending on site specific conditions. Measurement and payment may be based on a time and materials compensation depending upon equipment, labor, and or material stated in the bid documents. 3 1.3.2.6.4 Placement of Embankment 1.3.2.6.4.1 General Placement of Embankment is the process of constructing a foundation for the track structure where the natural ground surface is below the desired elevation of the finished subgrade. Materials are placed so that the designed Embankment Section and subgrade elevation are obtained. Materials to be placed are typically identified as either "Common Material (Soil)" or "Rock", and are generally obtained from approved on-site excavation or approved on or off-site borrow sites. Materials consisting of "Common Material" should satisfy the soil characteristics designated for embankment fill as specified in Table 1-1-10 in Section 1.2.3 to achieve appropriate design performance objectives. 1.3.2.6.4.2 Procedures Placement of Embankment should be performed in accordance with the project plans or as directed by the Engineer. Embankment should be completed as far as is practical using suitable excavation material before borrow materials are obtained from outside sources. Site conditions may prevent total utilization of excavated material and necessitate use of borrow. However, consideration of the most efficient utilization of excavated materials is important if the Contractor’s price for supplying borrow material is higher than his price for excavated material. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-47 4 Roadway and Ballast The Contractor should maintain all working surfaces in areas where embankment placement activities are being performed in a well-drained condition at all times. Embankment surfaces should be shaped and compacted during placement to facilitate positive drainage and minimize absorption of water. Properly drained work areas typically allow construction to resume more quickly with less waste following rainfall events. Side and/or slope ditches, both above or at toe of embankments, should be constructed in a timely manner during the course of construction to promote positive drainage of the site and facilitate placement of the embankment. Care should be taken during placement of embankment material to avoid adverse impacts to previously constructed ditches, drainage structures, or impede natural surface watercourses. The Contractor should maintain haulage route surfaces to avoid rutting and water ponding. Ruts or depressions that are allowed to remain on the working surface of the embankment will cause water pockets and subgrade instability. The Contractor should be prepared to supply and apply water or other means of reducing dust at the placement point or on haul roads when required by the Engineer or applicable environmental permits. Final acceptance of embankment materials should only be made after the materials have been dumped, spread, and compacted in place. Rejection by the Engineer may be made at the source, on the transporting vehicle, or in place. Removal and disposal of all rejected embankment material should be at the Contractor’s expense. The Contractor should inform the Owner of proposed off-site borrow sources, and allow sufficient time so that the suitability of the material for use as fill can be investigated. The Contractor may be required to provide the necessary personnel and equipment to perform adequate investigation and sampling. Responsibility for this investigation should be defined in the construction documents. Representative samples of borrow materials should be taken for laboratory testing to establish suitability of the material for use on the project. "Fill Material" should be composed of "Common Material" or "Rock" as defined herein. In general, material such as topsoil, loam, uniform fine sand, silt, and clay should be avoided. This recommendation can be modified and adjusted on a site-specific basis depending upon local conditions, availability of borrow materials and prudent design of the fill. However, the soil types named above are those usually found to be unsatisfactory for fills, and use within the track subgrade area should be avoided if at all possible. Borrow areas should not be excavated until they have been properly cleared and stripped, and mapped as required by the contract documents. Borrow areas should be adequately drained during borrow operations, to prevent saturation of the proposed fill materials. At all times the Contractor should operate sufficient equipment to compact the fill at the rate at which it is being placed. Choice of compaction equipment should be made by the Contractor and approved by the Engineer. Typically, a sheeps-foot roller would be applicable for cohesive soil materials. A vibratory compactor would be appropriate for granular fill materials. The chosen equipment must be capable of achieving the minimum compaction requirement specified in the contract documents. 1.3.2.6.4.3 Construction of Fills with Common Material Fills should be built by placing common material in successive layers over the full width of the embankment. Where segregation is a concern, reblending for uniformity may be required. Where fills are designated to have stabilization berms at or adjacent the toe of fill, the berms must be raised at the same time as the central portion of the fill. All earth-hauling equipment should be routed uniformly over the entire width of fill to obtain uniform compactive effort from the earth-haul traffic. Where new fill is placed against an existing slope, all vegetation should be removed, the surface deeply plowed or stepped, and the new material thoroughly mixed with the old material to a horizontal distance approved by the Engineer. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-48 AREMA Manual for Railway Engineering Roadbed Soil lumps larger than 8 inches in size should be broken by scarifiers or disks before compaction. The thickness of each layer should normally not exceed 8 inches before compaction. Depending on the type of fill material and the type of compacting equipment used, layers in excess of this thickness may be allowed with the specific approval of the Engineer. In this case the Engineer may require the Contractor to perform rolling tests on the fill material to determine acceptable layer thickness and minimum number of complete passes of the compacting equipment to achieve the specified compaction. An additional rolling test should be considered whenever either fill material or compacting equipment changes throughout a project. Each layer should be fully compacted by approved mechanical compacting equipment before the next layer is placed. A fully compacted layer typically should have a dry density of at least 95% of the maximum dry density as determined by the current revision of ASTM Specification, Designation D 698T, Moisture-Density Relations of Soils (Proctor Test), or 90% of ASTM D-1557 Moisture-Density Relations of Soils (Modified Proctor Test). When the specified compaction density is not being obtained, placing of fill should be stopped and the material in place should be scarified, adjusted in water content, if necessary, and re-rolled until the required compaction is obtained. Alternately, material not fully compacted may be removed and replaced by the Contractor at his expense. If before acceptance of the work, softening of the subgrade surface takes place under construction traffic to a degree unsatisfactory to the Engineer, the soft material should be reworked or removed and replaced as indicated previously. The cost of all such work should be borne by the Contractor. In general, material approved for fill should have a natural water content close to the optimum water content for compaction. When required, the Contractor should add water uniformly by means of an approved distributor to any fill material, which is deficient in water content for compaction. If the fill material is too wet, it should be scarified or disked and aerated until the proper water content is attained. With the approval of the Engineer, drier soil may be blended with wet fill to achieve a water content suitable for compaction. It is important to note that Soil strength depends on density and water content relative to optimum water content. 1 It should be noted that the ability to obtain desired compaction levels with certain types of soils may be improved by adding lime, fly-ash, or other cementitious products. The use of such additives should be properly engineered. 3 1.3.2.6.4.4 Winter Grading with Common Materials With the permission of the Engineer, the Contractor may place embankment during freezing weather. For this purpose the Contractor should provide the necessary amount of earth moving and compacting equipment to assure continuous operation during freezing weather in both excavation and embankment areas. All embankment material should be compacted before freezing. If materials freeze before the required compaction is attained, the placement of embankment should be stopped and the frozen material should be removed at the Contractor’s expense before construction resumes. No snow, ice, or frozen material should be placed in the embankment, nor should embankment be placed on materials incorporating snow and ice. With proper guidance and expertise, it is possible to satisfactorily place embankment in temperatures down to 0 degrees F. A key consideration is access to borrow material known to have near optimum water content (as water may not be added and drying of material in transit is minimal). 1.3.2.6.4.5 Construction of Fills with Rock This section discusses some of the general issues associated with construction of fills using rock. While applicable for any rock fill embankment construction, the guidelines below become increasingly important as fill size increases. In general, construction of fills using rock, both uniformly graded stone, and non-uniform shot rock, is less complicated than fill construction using soil materials. This is due to the less critical role that moisture content plays in achieving adequate compaction and relative density. Placement and compaction of rock fill material is typically less affected by inclement weather than construction with Common Material. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-49 4 Roadway and Ballast Rock fill should be transported and placed on site using methods approved by the Engineer. If well-graded rock fill is specified, placement by end dumping should be avoided to reduce potential segregation of the material. Segregated material should be re-blended, or otherwise modified by the addition of finer grained materials prior to acceptance. The purpose of this practice is to reduce later migration of fines into poorly graded zones within the fill. Rock fill should be spread in the specified maximum loose lift thickness in near horizontal layers for the full width of the design cross-section. The maximum loose lift thickness of rock fill typically should be no more than the size of the maximum individual rock particle plus 30%. As example, shot rock fill with a maximum particle size of 24 inches, would equate to a maximum loose lift thickness of about 30 inches. Each loose lift of rock fill should be compacted by full coverage with approved construction equipment until stable as determined by the Engineer. In general, rock fill should be compacted using heavy pneumatic tired equipment, tracked equipment, or vibratory roller type equipment. As example, a typical 30" rock fill lift should be compacted with not less than four complete passes of a crawler type tractor weighing at least 25 tons. However, the Engineer should be the final judge regarding the actual compactive effort required. The void space within the rock fill matrix, the degree of compaction, and the overall fill height will influence the degree to which the fill consolidates and settles. In general, some amount of settlement should be expected for embankments constructed using rock fill, particularly if the fill has the potential for periodic saturation. Depending on the size of the void space within the rock fill mass, a layer of geotextile, or a graded granular filter layer may be warranted along the interface with adjacent finer grained materials. This is to reduce the potential for migration of finer material into the rock fill void space. As noted above the use of a well-graded rock fill material for embankment construction can help reduce this potential problem. While moisture content of rock fill material is generally less critical to proper placement and compaction, repeated saturation and drainage of rock fills can result in consolidation and settlement. In some instances, the addition of water may aid in consolidation of the rock fill mass during initial compaction operations. 1.3.2.6.4.6 Widening of Existing Embankment Fills The purpose of this section is to discuss some unique aspects of placing fill material for widening existing embankments. Reference should be made to the recommendations presented above concerning general criteria for fill placement and compaction. Fill placement against an existing embankment should be performed using notching/benching techniques that allow newly compacted fill to be constructed against existing stable embankment materials. These grading operations should be performed using techniques that avoid undermining existing track structure, yet addresses issues such as; clearing of the embankment slope, maintenance of drainage from within the existing embankment, and preservation of existing embankment support elements. Dependent upon site specific conditions, preparation of the slope and site should include removal of standing vegetation and topsoil in a manner which does not destabilize the slope, This may require postponing the grubbing of slopes until immediately prior to performing the notching/benching activities. Fill placement against an existing embankment should include notching, keying or benching of the new material into the existing slope as filling progresses. The lateral extent of the notches, keys or benches, and the associated vertical cut in the existing slope, will depend on the depth needed to remove soft or loose material and key into firm or competent material. In general, the size of such notches, keys or benches is approximately 3 feet horizontally depending upon issues such as slope geometry, undermining of track operations, etc. The actual geometry should be approved by the Engineer. During fill placement, the width of the working surface, including the new fill and the notch or key, should be adequate to facilitate safe equipment operation and proper mechanical compaction of the fill. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-50 AREMA Manual for Railway Engineering Roadbed If the existing embankment consists of granular material that drains easily and is widened by using lean clay material there is the potential that water accumulation may occur along the non-uniform soil interface that may result in slope stability problems unless drainage provisions are included in the construction. It is recommended that the widened embankment be constructed of soils with characteristics similar to the existing embankment. 1.3.2.6.4.7 Fills in Soft Foundation Areas Soft soil conditions that extend to shallow and great depths may unexpectedly be encountered during construction. Depending on the depth and extent of such conditions, a variety of treatments may be appropriate. In the case of shallow conditions, when the Engineer does not require subexcavation as a specific foundation stabilization method and drainage of the foundation soils is impractical, it may be appropriate that an initial lift of stabilization material may be installed. This initial supporting layer of fill is commonly termed a "bridging lift". Normally this layer consists of granular or well graded rock material that is placed over the full foundation area of the proposed fill. Its surface should be compacted. It is important to note that a variety of geosynthetic materials are available for use in formation of "bridging lifts". Thereafter the remainder of the fill should be built up in layers to the specified thickness. In the case of deep soft conditions, more sophisticated solutions may be required. These may include staged construction, surcharging, berm or buttress construction, deep foundation systems, and/or foundation drainage techniques. Reference should be made to the design section of this text for recommendations concerning such methods implementation. 1.3.2.6.4.8 Trimming All cuts, fills and ditches should be left in a neatly trimmed condition to the specified widths, elevations, and slopes. Borrow areas should be graded and finished to a neat and regular slope. 1 All waste and stockpile areas should be left in neat, trimmed conditions to the satisfaction of the Engineer. Positive drainage of all areas should be provided. 3 1.3.2.6.4.9 Measurement & Payment The pay for embankment construction is typically measured on a cubic yard basis (i.e., as measured either in place or in the cut section). Payment is made only for quantities of embankment required for the proper completion of work items covered in this section. Additional embankment undertaken by the Contractor carelessly or solely for his benefit, such as required for haul roads, relocation of equipment, and backfilling operations, should not be considered or measured for payment. Care should be taken in structuring bid documents and specifications to avoid creating a scenario where the Owner pays for excavation and also pays for placement of the same material as embankment. 1.3.2.6.5 Placement of Sub-ballast Material 1.3.2.6.5.1 General The purpose of sub-ballast is to provide a separation layer between the subgrade and ballast using a material with strength equal to or greater than the subgrade. Track laid on prepared subgrade without sub-ballast tends to drive the ballast and/or ties into the roadbed forming depressions which later develop into ballast pockets requiring additional maintenance. Sub-ballast can be considered as a component of either roadbed or track construction depending on the project. 1.3.2.6.5.2 Materials and Procedures Sub-ballast material should meet the requirements for quality and grading set out in Part 2, Ballast . © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-51 4 Roadway and Ballast Sub-ballast material should be placed to the cross sections and tolerances shown on the plans. Placement should be in layers not exceeding the thickness that can be effectively compacted to its full depth with the available construction equipment. Rutting or disturbance of the completed subgrade should be avoided. Disturbed or rutted subgrade materials should be either properly reworked or removed from the fill and replaced. 1.3.2.6.5.3 Measurement and Payment The measurement for sub-ballast material is commonly made on a net ton or in-place cubic yard basis per the design cross-sections. Payment should be based on quantities from certified scale tickets or as measured and calculated in-place per the design cross sections by the Engineer. Said unit price should include the entire cost of supplying, hauling, placing, moisture conditioning, blading, and compacting sub-ballast material. 1.3.2.6.6 Seeding and Mulching 1.3.2.6.6.1 General The purpose of seeding and mulching is to establish managed vegetative growth to quickly stabilize exposed earthen surfaces. It is recommended that all earthen slopes and surfaces disturbed or constructed under the contract be seeded and mulched. 1.3.2.6.6.2 Materials a. Specifications for seed, fertilizer, and mulch, as well as their rate of application should conform to recommendations of the applicable State or Provincial Department of Transportation, the United States Department of Agriculture, or be obtained from a qualified agricultural consultant with experience in the general vicinity of the project. Requirements of applicable project environmental permits should be considered. b. Seed should be of high grade and of known vitality, purity, and germination and should be delivered in bags or containers bearing seed tags as required by law, showing percent of germination, purity of seed, and percent of weed seed. c. Fertilizer should be of standard commercial grade with the analysis shown on each package. If delivered in bulk there should be a material certification provided with each delivery. Any fertilizer which becomes caked or otherwise damaged should be rejected. d. Typical mulches include hay, straw, wood cellulose fiber, and recycled vegetative material. e. It should be noted that on a site-specific basis, erosion resistant specialty products and application methods are available to aid in site revegetation. 1.3.2.6.6.3 Procedures a. Consideration should be given to the stockpiling of topsoil removed during stripping operations and to its redistribution on disturbed or constructed surfaces. b. The surface to be seeded should be dressed to eliminate gullies on cut and fill slopes. Dressing should be done by a drag or blades to produce a uniform surface. Plowing or disking is generally not necessary except where construction operations have packed surfaces too hard to permit plant growth. c. Seed and fertilizer should be applied to take advantage of favorable weather conditions. It should be applied by a method which provides uniform distribution in accordance with the appropriate specification. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-52 AREMA Manual for Railway Engineering Roadbed d. It is advisable to set minimal plant establishment rates in the specifications to guarantee performance. In such instances the Contractor may be required to redress and reseed the subject areas. e. Care should be taken to avoid contaminating the sub-ballast and ballast sections of existing or recently completed trackage in the work zone with seed, mulch, or other material. 1.3.2.6.6.4 Measurement and Payment a. Seeding and mulching typically are measured by the acre or fraction thereof so treated. b. The unit price for seeding and mulching should include the entire cost of preparing the ground, furnishing, hauling and placing materials discussed above and furnishing all labor, equipment, tools, and incidentals necessary to complete the work. SECTION 1.4 MAINTENANCE 1.4.1 MAINTENANCE OF ROADBED (2007) 1.4.1.1 General a. The roadbed is that portion of the track structure beneath the ballast section and within the zone of influence of live traffic loads, including foundation support. The performance of the roadbed is greatly influenced by the following factors: 1 (1) The presence of excess moisture in the roadbed and the site specific drainage characteristics of the roadbed and ballast section. 3 (2) The engineering properties, thicknesses, and in-place densities, of the various materials. (3) The effect upon the roadbed of environmental factors: especially, precipitation, temperature, and the presence of groundwater. (4) The magnitude, speed, and repetition of the rail traffic loads. (5) The characteristics of the track superstructure (rail and ties), ballast and sub-ballast; especially, the thickness of the ballast section. b. Of all the factors affecting roadbed performance, the presence of excess moisture in combination with one or more other factors is the root cause for most roadbed maintenance problems. Therefore, the design and maintenance of drainage away from, or out of, the track foundation materials is of primary concern and paramount to the success of most corrective measures. c. The roadbed consists of the natural foundation materials (native soil or rock), and the overlying imported soils extending downward from the bottom of the ballast and sub-ballast section that is within the major zone of influence of live traffic loads. In new construction and in some existing tracks, the roadbed is separated from the ballast and sometimes sub-ballast by distinct boundaries. However, in most cases, there are no distinct boundaries between layers of the ballast, sub-ballast, and roadbed. d. The zone of significant influence from train loadings extends to an approximate depth of five feet beneath the ballast section. Beneath this level, the stresses from live traffic loads are relatively low. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-53 4 Roadway and Ballast e. The roadbed can be composed of a wide variety of materials. The most predominant materials are local native soils and soils imported from nearby sources. In the upper layers of the roadbed, imported materials including cinders, sands, and pit run gravels may be found intermixed with the ballast materials that have been placed during track surfacing cycles. f. The composition and thickness of the materials and the drainage conditions existing in the upper two feet of the roadbed are extremely important because of the high stresses from track loads and exposure to environmental factors. Roadbed induced track problems such as loss of line, surface, gauge, mud pumping and ballast fouling in most cases can be traced to one or a combination of deficiencies in the material properties, thickness, or drainage characteristic within the upper two feet of the roadbed. Therefore, most roadbed maintenance measures may need to be concentrated at making improvements to the upper two feet of the roadbed and especially to the interface between the ballast (or sub-ballast) and the roadbed soils in addition to making improvements to the drainage. g. Additional details regarding the design and construction of roadbeds are discussed in greater detail in Section 1.1 through 1.3 of this Manual. 1.4.1.2 Existing Roadbeds a. The great majority of railroad roadbeds in service today were originally constructed many years ago and without the benefit of modern methods and equipment, or the benefit of current engineering understanding. In many instances the track was built directly on top of the native loose soils or on nearby borrow soils that were loosely dumped and spread in place to form narrow shallow fills with steep side slopes. Little attention, if any, was given to selecting soils with more favorable roadbed properties or compacting the roadbed soils before constructing track. However, over the years, these roadbeds have tended to become firm and stable from the compaction and consolidation effects of rail traffic and from the numerous surfacing cycles that have contributed granular materials and ballast to the roadbed. Subsurface exploration of existing roadbeds will often reveal several layers of soil, imported granular materials, and old ballast of varying thicknesses and depths. An example of a distorted roadbed and method of reporting such conditions is shown in Figure 1-1-12. LOOKING RAILROAD DIRECTION ________________________ BALLAST AND LOAM 0 1 BALLAST AND LOAM LOAM FOULED BALLAST SLAG WITH SOME LIMESTONE 2 ND EL TA V DIR GRA Y D SAN DIRTY SANDY GRAVEL CLEAN SANDY GRAVEL 3 4 5 GRAY MOTTLED CLAY (VERY SOFT) 6 7 STABLE FOUNDATION MATERIAL 12 11 10 9 8 7 6 5 4 3 2 1 0 1 FEET 2 3 4 5 6 7 8 9 10 11 12 Figure 1-1-12. Example of Distorted Roadbed Cross Section b. There are many instances of a continual loss of line and surface accompanied by mud pumping, often referred to as “chronic spots” or “soft spots.” Subsurface explorations of these chronic problem areas will often reveal unsuitable materials at great depths mixed with ballast sometimes referred to as “ballast pockets.” An example cross section of typical ballast bowl or pockets is shown in Figure 1-1-13. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-54 AREMA Manual for Railway Engineering Roadbed DISPLACED SUBGRADE (SHOULDER HEAVE) ORIGINAL TOP OF SUBGRADE BALLAST SECTION BALLAST POCKETS TRAPPED WATER Figure 1-1-13. Example Cross Section of Displaced Roadbed and Ballast Pocket c. Another problem with some older fills is a cinder fill fire. Cinders were used as fill materials in a number of older fills. The cincers frequently have an organic component related to unburned coal. The pressure of a fill is not believed to be sufficient to ignite these fires. However, some are undoubtedly started by outside combustion sources such as lightening and range fires. These fires can be spotted before they get very large by their effect on vegetation or snow cover and their emission of a unique acetylene odor. These fires are nearly impossible to put out with water. The best way to stop the fire is to dig out the cinders and replace with a better fill material. It is possible to stop smoldering or burning by capping with cohesive fill that cuts off the supply of oxygen. However, a small leak in the oxygen cap will limit its effectiveness to prevent burns. The burning cider material can cause consolidation of the fill, which could result in settling of the track structure. 1 1.4.1.3 Identifying Roadbed Instability a. b. Initial evidence of roadbed instability is a continual loss of line and surface despite satisfactory rail and tie condition and an assumed adequate ballast section. Loss of line and surface may continue even after several ballast applications followed by lining and surfacing operations. A muddy, fouled ballast section and heaved track shoulder (see Figure 1-1-13) are other indications of roadbed instability. Excess moisture and poor drainage conditions are so closely related that evidence of either can almost be considered as an indicator of roadbed instability. However, caution should be used before identifying a muddy fouled ballast section as roadbed instability. In some cases internal abrasion and weathering of the ballast or windblown dirt and car droppings will cause a fouled ballast section and give the appearance of roadbed instability. If any doubt exists as to the cause or extent of roadbed instability; subsurface explorations, sampling and geotechnical testing of the roadbed materials should be performed. The technique of excavating a trench several feet deep across the width of the ballast section for the purpose of exposing the layers, thicknesses, and relative positions of the roadbed materials is strongly recommended as an aid in the planning any roadbed corrective measures. See example in Figure 1-1-12. Vertical and lateral displacements of the roadbed as evidenced by loss of track line and surface may actually originate beneath the roadbed zone. The possibility that embankment, slope, or foundation stability problems exist and are contributing to roadbed displacements should be investigated and analyzed before attempting roadbed corrective measures. Refer to Article 1.2.2 and Article 1.2.3 for further information. 1.4.1.4 Types of Roadbed Instability a. Possible indications of unstable track include the loss of surface, line and gauge, and fouled ballast. These may be caused by the following roadbed conditions: (1) Migration and pumping of the subgrade and roadbed materials into the ballast section. The ballast section becomes contaminated with fine materials resulting in poor drainage, a dramatic decrease in the overall strength of the ballast system, and a loss of surface and line. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-55 3 4 Roadway and Ballast (2) The vertical and lateral displacement of the roadbed soils and roadbed materials as reflected in surface and line of the track. (3) Frost heaving of subgrade soils and roadbed materials. b. The presence of excess moisture in the roadbed is the single most important factor contributing to roadbed instability. An increase in the weight, speed, and frequency of traffic will also contribute to overstressing the subgrade and roadbed material and pumping fines upward into the ballast. Frost heaving is heavily dependent on unfavorable environmental and roadbed material conditions and to a lesser extent on traffic. 1.4.1.5 Migration and Pumping of Roadbed Soils and Materials a. Subgrade and roadbed soils may be pumped up into the ballast voids by the action of repetitive wheel loads. Fine sands, silts, clays, and clayey silts are highly susceptible to pumping when excess moisture is present in the roadbed. b. Pumping and migration of roadbed soils can be controlled or eliminated in existing track by the methods listed below: (1) Improving the drainage to keep the roadbed dry. Both surface and subsurface drainage improvements will reduce pore water pressure build up and will increase the strength of the roadbed. Surface drainage of the roadway is described in Article 1.2.4. Improvements to subsurface drainage are described in Article 1.2.4.2. Before considering subsurface drainage, an adequate field investigation and drainage . system design should be performed. Lateral and longitudinal subdrains consisting of perforated pipes, geotextiles, and free draining backfill materials can be used in combination to improve the roadbed drainage. (2) Removing the track and fouled ballast and reconstructing the roadbed by adding a compacted granular sub-ballast layer of sufficient thickness that will function as a firm, load bearing layer that diverts water away from the roadbed. The sub-ballast also functions as a filter against the intrusion and migration of roadbed and subgrade fines. It is recommended that the sub-ballast consist of a well graded crushed rock that is consistent with the design recommendations presented in Section 2.11, Sub-ballast Specifications. It is recommended that the sub-ballast layer be at least 6 inches thick and should be placed and compacted in accordance with Section 2.11. (3) Removing the track and fouled ballast and reconstructing the roadbed with a layer of high strength, flexible or rigid stabilized material. Hot-mix asphalt concretes have been used with success as a flexible stabilized roadbed. Lime treated soils, soil-cements, cement treated bases, and Portland cement concretes have been used as rigid stabilized materials. The stabilized materials should be of adequate thickness and include provisions for drainage and prevention of pumping. (4) Placing an appropriate geotextile or filter fabric (combined with removal of fouled ballast) below the ballast section. The application and physical requirements for geotextiles are given in Part 10, Geosynthetics. With careful planning, the geotextile may be effectively placed during an undercutting or sledding operation that avoids total removal or lifting of the track. The primary purpose of the geotextile is to function as a filter that separates the ballast and sub-ballast from the fine grained roadbed soils. The geotextile may also function to reinforce the roadbed and reduce ballast penetration into the roadbed section. (5) Injecting chemicals into the roadbed. Lime, lime/fly ash, and cement slurries injected at relatively shallow depths and close spacing have been used with some success to reduce pumping and prevent migration of fines into the ballast section. Use of chemical injection should be preceded by a program of subsurface exploration, sampling, and laboratory testing to determine if the chemical will react with and improve the roadbed material and soil. (6) Increasing the thickness of the ballast section by track raise. (7) Applying and compacting a layer of well graded sand utilizing large on-track equipment similar to an undercutter. This equipment is capable of lifting the track as a unit, removing fouled ballast, laying and compacting a sand layer and replacing the ballast. This technique and equipment has been used with success in Europe. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-56 AREMA Manual for Railway Engineering Roadbed 1.4.1.6 Vertical and Lateral Displacement of Roadbed Soils and Materials a. Areas where track settles repeatedly under traffic requiring frequent surfacing and lining can be caused by deformation of weak and plastic subgrades and roadbed materials. The deformation may be accompanied by the roadbed squeezing/pumping up between the ties or out at the end of ties, or bulging on the upper roadbed side slopes. These track areas that require frequent surfacing are often called “soft spots”, “chronic spots” or unstable roadbed. b. Soft spots usually occur where there are low strength and/or saturated subgrade soils and roadbed materials that permanently deform under traffic causing a local depression in the roadbed beneath the track. c. Soft spots or unstable roadbed are believed to develop as follows: (1) An existing track or recently constructed track is located over plastic subgrade or roadbed materials that loses strength as a result of increase in moisture content. In most cases the roadbed and subgrade become wet resulting in a loss of strength under repeated train loadings. Traffic loads transmitted through the rail, tie and ballast structures overstress the roadbed and subgrade resulting in permanent deformation and the creation of a depression that traps water. Trapped water facilitates further loss of subgrade strength, resulting in track movement. (2) The continual cycle of repetitive wheel loads combined with saturation results in the roadbed becoming plastic and displacing or squeezing laterally beyond the ends of the ties to the track shoulder. Frequent additions of ballast combined with surfacing supplies material that entraps more water, all of which permits the deformation and displacement to continue. (3) A ridge of displaced roadbed materials and soils is raised around each depression. Displaced soils are replaced with ballast that forms a large ballast pocket capable of holding greater amounts of water. Roadbed materials and soils at the base of the pocket continue to be saturated, weakened, and displaced, all resulting in a selfperpetuating condition. d. Corrective techniques for soft spots and unstable roadbed can be divided into those that must be performed by removing the track and those that can be performed without removing the track. e. When the track cannot be removed; displaced and deformed roadbeds, soft spots, and ballast pockets may be corrected by solutions such as: (1) Improvements to surface and subsurface drainage. The surface drainage can be improved by constructing a system of ditches parallel to the roadbed with catch basins, culverts and other surface drainage facilities that will quickly dispose of surface water away from the track roadbed. However, caution should be used when constructing parallel side ditches to avoid undermining adjacent roadbeds. Subsurface drainage improvements should be preceded by a thorough field investigation including subsurface explorations, trenches to expose the roadbed, laboratory testing and an analysis to design any needed subsurface drainage system. (2) Subsurface drainage systems that are properly installed can effectively drain water that is entrapped within the subgrade soil and improve the bearing capacity of the roadbed materials. Subsurface investigations performed by digging a cross trench will often make the problem apparent. The solution to the problem sometimes consists of the installation of a French drain within the exploratory ditch. The exploratory ditch should be dug deep enough to get to the bottom of the water pocket (ballast bowl) and then backfilled with a free draining granular material. To prevent clogging this material should be appropriately graded or protected with filter fabric. Installation of a perforated pipe to speed drainage can increase its effectiveness. (3) Another subsurface drainage system that may be appropriate to improve subgrade stability involves the installation of a French drainage system parallel to the ends of ties with periodic lateral drain pipes installed to drain into the adjacent railroad ditches. (4) In many cases improvements to the drainage can be combined with other corrective techniques such as: © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-57 1 3 4 Roadway and Ballast (a) Geotextiles, geogrids and other reinforcing materials may be installed in combination with undercutting, sledding or other track raise techniques that avoids the total removal or shifting of the track. The geotextile and geogrid used in this manner must possess the strength and other material properties necessary to act as a reinforcement capable of bridging over the unstable area or soft spot. The geotextile and/or geogrid should at least be 8 inches and preferably 12 inches beneath the bottom of the tie, at least deep enough to avoid damage by surfacing equipment. (b) Stabilization of the roadbed by lime, lime/fly ash, or cement injection. This treatment technique can be used for void filling purposes and moisture reduction or for ground improvement due to chemical reaction between the admixture and the roadbed materials. Use of lime, lime/fly ash or cement injection should be preceded by a program of subsurface exploration, sampling and laboratory testing to determine if the lime, lime/fly ash or cement will react with and improve the roadbed soils and materials. The injection of lime and lime/fly ash slurry into unstable roadbeds, soft spots and ballast pockets has been most successful with certain reactive clays, granular materials, cinders, and silt materials. A grouting specialist should be consulted to determine appropriate applications and expected results. Lime slurry chemically improves reactive soils and increases the strength at depths to 40 feet. Double lime injection is often required to improve shallow soil problems in areas where stresses are highest. (c) Construction of shoulder berms. Railroad roadbeds constructed on shallow narrow embankments often become unstable due to a combination of poor roadbed materials and a lack of lateral confinement extending beyond the end of the ties. This condition can be corrected by the addition of small berms to the roadbed side slopes. The effect of the berm construction on the roadbed drainage should be carefully analyzed prior to building any berms. Stabilization berms should always be kept below the level of the ballast and the upper portion of the sub-ballast. The berms should have good cross slope to promote drainage. f. When the track must be removed; displaced and deformed roadbeds, soft spots and ballast pockets can often be corrected by methods such as: (1) Improving the surface and subsurface drainage conditions as described in Article 1.4.1.5.b.1, combined with excavation and wasting of the fouled ballast and roadbed material and replacement with properly placed and well compacted suitable soils and a sub-ballast layer as described in Article 1.4.1.5.b.2 or replacement with a high strength stabilized layer of sub-ballast as described in Article 1.4.1.5.b.3. (2) Excavation of the ballast and disturbed roadbed materials. Reconstruct with compacted fill materials. Place geotextile and/or geogrid at the ballast/roadbed interface or the sub-ballast/roadbed interface. Properly designed and installed geotextile will separate and act as a filter preventing the fine roadbed and soil materials from migrating into the ballast section. Geotextiles and geogrids can be installed as needed to reinforce the ballast/roadbed system. Improvements to surface and subsurface drainage conditions should be performed as required to avoid future loss of subgrade strength. (3) Injection or mixing of the track subgrade and foundation soils with lime, lime/fly ash, or cement in combination with corrective methods listed above. Use of chemical injection or mixing should be preceded by a program of subsurface exploration, sampling and laboratory testing to determine if the chemical will react with and improve deficiencies within the track subgrade and foundation materials. 1.4.1.7 Frost-Heaving 1.4.1.7.1 Causes and Occurrence a. Frost-heaving of roadbed and ballast is caused by the simultaneous presence of fine-grained material, water and freezing temperatures. b. The degree of frost heave in soils increases with increasing moisture content. Rough track is caused when differential heaving of subgrade soils develops over short distances along or across the track. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-58 AREMA Manual for Railway Engineering Roadbed c. These differences may be more or less than the uniform track heaving that seasonally occurs. More heaving than average (rise in track) may occur typically at poorly drained areas (such as farm and road crossings). Less heaving than average (dip in track) may occur at culverts and road crossings where de-icing chemicals are applied. A change from a heaving to a non-heaving condition may occur at bridge approaches or at the end of rock cuts. A good proportion of all types of heaving occur in regular track where no particular features are present but a change in subgrade soil occurs. Before deciding on treatment it is important to determine whether the rough track condition is created by a rise or a dip in the track. d. Rough track, caused by frost-heaving, causes excessive wear on both track and rolling stock and increases the danger of accidents unless slow orders are applied or track conditions improved. The most common method of improving the track surface is by the temporary shimming of ties. However, this is expensive, reduces the service life of wood ties, and requires an experienced labor force to be kept on hand, particularly at the start of freezing and thawing seasons when heaving and subsidence occur relatively suddenly. Concrete ties cannot be shimmed more than a small amount. For these reasons, the methods of managing track-heaving discussed below should be considered as an alternative to temporary shimming. 1.4.1.7.2 Track Betterment a. Frost-heaving under track may be reduced or made more uniform by influencing one or more of the conditions causing it. This may occur as a side effect of work done primarily to improve other track conditions: (1) Cleaning of fouled ballast will remove fine-grained material and reduce capillary rise of water. (2) Addition of a ballast lift will increase insulation that reduces frost penetration into subgrade soil. 1 (3) Addition of bank-widening material may reduce frost penetration into track shoulders. b. While beneficial, the overall effect of these measures on frost-heaving is limited. Where heaving of track must be eliminated, a more direct approach to the problem is required. 3 1.4.1.7.3 Replacement of Frost-Heaving Material a. Although expensive under an operating track, replacement of frost-susceptible subgrade soil with a less susceptible material is a method of treating the problem. Steps to be taken are: (1) When frost-heaving and shimming are at a maximum in early spring, find by sighting along track whether the trouble spot is caused by a rise or a dip in the track. Mark the location according to the procedure shown in Figure 1-1-14. At the same time, excavate to find the maximum frost depth. (2) After all frost is out of the ground, remove track and excavate over the length of section (A) in Figure 11-14 to remove the subgrade soil to a depth of at least 60% of the maximum frost depth. In both transition zones (B), taper the excavation uniformly to zero at the outer ends. Carry the excavation to the shoulders for proper drainage. (3) Backfill to grade level with thoroughly compacted layers of non-heaving material (Column 4 of Table 11-10). (4) Replace sub-ballast, ballast and track. b. Under special or extreme conditions, the installation of a layer of insulating material in the roadbed should be considered. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-59 4 Roadway and Ballast RISE Nail or Stake Maximum Height of Shims 6 Cribs B 6 Cribs A Track Maximum Height of Shims B DIP Nail or Stake Nail or Stake End of Shimming Track 12 Cribs 12 Cribs B A B ZONE A - FULL EXCAVATION OR TREATMENT ZONE B - TAPERED EXCAVATION OR 1/2- STRENGTH TREATMENT Figure 1-1-14. Method of Marking Track for Treatment of Frost Heaving 1.4.1.7.4 Drainage Drainage improvement measures could be considered to reduce track heaving when ditches are less than several feet below top of sub-ballast level or if water pockets exist within ballast bowls under the track section. Depending on site conditions, improvements can include deepening of the railroad ditches. Additionally, consideration could be given to the excavation and replacement of track shoulder materials with clean granular material and installation of French drains transverse to the track alignment and at sufficient depth to drain of water pockets located within ballast bowls beneath the tracks. 1.4.1.7.5 Use of De-icing Chemicals a. The controlled application of de-icing chemicals can reduce heaving of track economically and reasonably effectively. Many chemicals have been tried for this purpose and ordinary crushed rock salt (NaCl) has been found to provide adequate results. b. The procedure shown in Figure 1-1-14 should be used to show where the salt is to be applied. A small quantity of salt is more effective than a larger quantity. c. Extensive use of salt or other de-icing chemicals for track de-icing may be restricted in some areas due to potential environmental impacts. These restricted areas may include areas where tracks cross water supply reservoirs, wetlands, etc. 1.4.1.7.6 Track Shimming Shimming is done to restore track surface and level to a safe condition. For the purpose, wood shims are installed on the top of ties which remain too low during track heaving. Shimming in no way reduces frost heaving and must therefore be done every winter. Procedures used to shim track are given in Chapter 5, Track. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-60 AREMA Manual for Railway Engineering Roadbed 1.4.2 MAINTENANCE OF ROCK SLOPES (2007) 1.4.2.1 Rock Falls a. Rock falls occur in cuts and on sidehill portions of railway lines in rough terrain. Where rock faces have been exposed for a number of years, single rocks or small groups of rocks are usually involved rather than the failure of entire slopes. For this reason, accurate prediction of rock falls is not always achievable. However, an experienced person (geologist or geotechnical engineer) can assess the risk of rock falls at particular locations and make recommendations, accordingly. b. Rock falls cost money due to regular maintenance, track patrols, train delays and rerouting required, and damage to equipment, and/or injuries and sometimes deaths. Safety is the main concern. 1.4.2.2 Methods of Treatment a. From an assessment of site conditions and performance, the most suitable treatment of a dangerous rock slope can be chosen. Treatment methods can include both preventive techniques and protective techniques. Methods of treatment should be considered in the following priority if the danger of rock falls is to be reduced: (1) Stabilization, or preventing rocks from moving out of place unexpectedly (as with overall slope flattening, rock scaling, and rock pinning or bolting). (2) Protection of track, or keeping rocks which do move out of place from reaching the track (as with netting, walls or rock sheds). 1 (3) Warning traffic when rocks arrive in the vicinity of track (as with slide detection fences). b. These techniques offer ways to manage the problem. Preventive measures address the cause of the problem. Protective measures or warning methods by themselves have no effect on the causes of danger. c. A general approach to rock fall hazard management is outlined in Figure 1-1-15. Remedial treatment methods are explained in Reference 40. d. Remedial work should be planned by railway engineering staff with particular experience in rock fall problems, using consulting advice where needed. e. Good records are the basis for good planning and for the setting of priorities. Records should include the time and exact location of accidents and delays to traffic, of all rocks found on track, and of the removal of ditch debris, as well as plans and maintenance required for all stabilization and protection installations. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-61 3 4 Roadway and Ballast Rock Fall Event Assess Site Conditions Angle, height, and condition of slope. Size and condition of rocks, Path of rock fall to track, Maintenance required. Engineering Judgment Scaling, excavation, drainage, shotcreting, support and restraint systems, buttresses, bolting, walls, or beams. Warning Methods Protection Methods Stabilization Methods Track diversion; Ditch shaped or bench formed to retain rocks; Net, fence, cables, blanket or wire mesh; Catch wall of concrete gabions, old rails, or rock; Shed or tunnel. Electric wire; Electric fence; Combined warning and protection. Figure 1-1-15. General Approach to Rock Fall Hazard Management 1.4.2.3 Follow-up Inspections A regular inspection should be made, preferably with an experienced person, to appraise hazards and decide on action and priorities required. Rock work is best done by experienced contractors, with a contract drawn up to allow flexibility in the work if conditions are found to be different than expected. 1.4.3 MAINTENANCE OF EARTH SLOPES (2007) 1.4.3.1 General a. Many earth slope failures are related to drainage problems. For maintenance of drainage see Article 1.4.5.1. b. Some roadbed failures can be prevented, solved or reduced by recognizing the problem and taking small steps before the problem gets severe. Some warning signs of slope instability are: • Cracks or seams in the roadbed especially near the ballast shoulder. • Trees leaning. • Ditches at the base of roadbed clogged because of bulges in fill. • Slip circles or slides on the embankment. • Seepage or extremely wet spots on the fill. c. Upon finding these conditions additional investigation should be done to determine the extent of the problem. Most of these conditions will only be made worse by unloading ballast at the top of the fill. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-62 AREMA Manual for Railway Engineering Roadbed d. Earth slope failures of this type can sometimes be contained by adding weight to the toe of the slide area. Care should be taken to establish the shape of the failure plane. An excellent material to add weight is rip rap, or shot rock fill. Granular material will allow any seepage water to drain from the face of the embankment foreslope. e. Reducing the moisture content of the fill by methods described in Article 1.4.1.3.a. can also help to stop or slow earth slope failures. 1.4.3.2 Methods of Earth Slope Restoration a. Methods of restoring slope stability are chosen on the basis of site observations and analyses made, and the suitability, feasibility and economies of the various alternatives. It is sometimes possible to gain time to implement these measures by temporarily moving the track around the area of instability. b. Methods are reviewed in Table 1-1-12. Table 1-1-12. Potential Methods for Stabilizing Earth Slopes Method Remarks Reducing Sliding Forces 1. Remove soil at top of slide area, flatten slope. Not always feasible. 2. Divert surface water flows to reduce erosion and infiltration. Use ditches or flumes, lined if necessary. Reduce infiltration by covering with materials that have low permeability. 3. Lower ground water level within sliding mass. Assumes slide mass will release pore water to drains. Drains can be excavated trench type drains or drilled in horizontal or vertical drains. 4. Eliminate leakage from culverts. Not always feasible. 3 Increasing Resisting Forces 5. Install pervious blanket. To keep slope surface material in place, preventing gullying and sloughing. 6. Construct berm over lower portion of slide area and beyond toe. Useful if feasible. Proportion berm on basis of stability analysis; ensure outer slope of berm is stable. Use free draining material or install granular blanket on slope beneath the berm to provide through drainage. Compact berm material. Riprap facing should be installed on toe of slopes that will be exposed to erosion by currents or wave action. 7. Install wall or crib (see Chapter 8, Concrete Structures and Foundations, Part 5, Retaining Walls, Abutments and Piers and Part 6, Crib Walls). Must be founded on stable ground. May be expensive. 8. Install vertical piles along track. Only successful if capable of resisting sliding forces. Piles act as pins to resist the shear forces along the failure plane. Piles may need to be drilled and socketed into bedrock. Piling can also be installed as adjacent pairs on either side of track and be tied together using either cable or rods that are installed under the track. Lagging can be installed between adjacent pins on the same side of the track to form a crib. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1 1-1-63 4 Roadway and Ballast Table 1-1-12. Potential Methods for Stabilizing Earth Slopes (Continued) Method Remarks Special Methods 9. Drill in tie-back anchors can be used with reaction blocks or with vertical beams and lagging. Must be designed by experienced engineer, especially if planned for permanent support. 10. Densify soil by vibration or compaction. Only possible with some granular soils. Specialized technique. 11. Grout, freeze, or apply electro-osmosis. Applicable only to special conditions. Very expensive. Experienced advice required. 12. Plant stabilizing vegetation on face of slope. Reduces water content of slope to shallow depths. Experienced advice required. 13. Soil Nail walls. Must be designed by experienced engineer, especially if planned for permanent support. 1.4.4 WIDENING OF CUTS (2007) 1.4.4.1 Rock Cuts a. Before excavation is planned, a survey should be made of the engineering characteristics of the exposed rock. Details of dip, joints, stratification, general competence and zones of weakness should be noted, along with the depth and type of overburden. b. The new slope should be suited to the characteristics of the rock in which it is made so that minimum maintenance is required in the future. For example, steeply dipping rock should be cut at the angle of dip. This may include benches, or a slope varying with the weathering resistance of the various rock layers. Drainage should be provided to reduce erosion and weathering. (See Article 1.2.2.1 for general design procedure) c. Methods of treatment to stabilize the slope or protect the track from falling rocks may be considered as an alternative to widening an unsafe rock cut, or applied in conjunction with excavation of the new slope. d. Blasting should be used only with approval of the Chief Engineer. The method of blasting chosen is most important in reducing future rock scaling and other maintenance work required. Blasting programs should be designed by qualified personnel. Control of flyrock is important. The use of presplitting for producing a clean finished rock face should be considered. 1.4.4.2 Earth Cuts a. Cuts are widened in railway maintenance work to improve drainage, increase the stability of slopes, reduce difficulties in maintaining track or clearing snow, or sometimes to obtain borrow materials. Whatever the reason, it is important that cuts in either earth or rock be afforded good drainage to provide stable cut backslopes. b. Article 1.2.2.3 provides general recommendations for use when choosing slopes that are safe for cuts in various soils. The reduction of seepage pressures within the slope by means of horizontal drains may be critical in cuts that have water-bearing soil layers. The selection of a safe cut slope may be derived from an inspection of nearby stable cuts or natural slopes in similar soils. Existing conditions that need to be taken into consideration include differences in the level of the groundwater table, vegetation, and other factors that influence instability. c. In making the cut, even temporary over-steepening (or undercutting) of potentially unstable slopes should be avoided, especially if the work is done during a wet season. Piles and lagging or crib walls can be used to © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-64 AREMA Manual for Railway Engineering Roadbed support the back slope of the ditch if there is restricted right-of-way width to cut an entire bank back to a stable slope (and temporary stability of an undercut slope can be assured). Drainage through the supporting structure should always be provided. d. In sidehill cuts, material excavated from the upper ditch or slope should not be placed on the downhill shoulder if avoidable. This practice adds weight to the shoulder and can cause failure of the downhill slope. Such excavated material should be wasted in an approved area. e. Vegetative root systems can help to bind a slope together while removing subsurface water that can also improve slope stability. It should be preserved to the maximum extent possible on stable slopes. Vegetative cover should be promptly reestablished on newly excavated cut slopes to minimize surface erosion and slope stability. Surface drainage in a widened cut should be planned according to Article 1.2.4.2. A drainage system which is balanced to handle both slope and roadbed drainage throughout the cut is essential. Drainage of water from the top of the slope should be intercepted and brought around or down the slope without causing surface erosion. 1.4.5 DRAINAGE AND EROSION CONTROL (2007) 1.4.5.1 Ditches and Drains a. b. c. Drainage is a very important function in providing for a stable track roadbed. Ditches of all types require periodic maintenance to preserve their function. Excess vegetation, talus, and erosional deposits should be removed to sustain positive ditch drainage. Excessive ditch scour/erosion must be corrected. Ditches not properly maintained may form wetlands. Permitting, which takes time and can have associated ecominc costes, is often required in advance of performing grading work to remove wetlands. Routine and timely ditch cleaning can sustain stable track subgrade conditions while avoiding those costs associated with the removal of wetland conditions. Less evident but also important is the periodic maintenance of subdrainage systems. Pipes, manholes and/or cleanouts should be periodically inspected and accumulations of sediment removed. It would be useful to maintain records of locations, date of inspections, types of maintenance performed and conditions. 1 3 It is not generally realized that drilled-in horizontal drains also require maintenance. On an as-needed basis, each pipe should be flushed or cleaned to remove materials that have accumulated within the pipes and are blocking the flow of discharge waters. Failure to remove these materials can lead to a buildup of seepage pressures within the track subgrade and embankment materials that can result in the redevelopment of the instability conditions which the drains were originally installed to relieve. 4 1.4.5.2 Erosion Control a. Erosion of right-of-way slopes and ditches is caused by rainfall and frost, and affected by the steepness and height of slopes. Resistance to erosion depends on the strength and cohesion of the slope or ditch soil and the presence of protective cover such as vegetation. b. Erosion resulting in downstream siltation is unacceptable. Erosion control is required in association with all new cut and fill slope construction. Additionally, periodic let down drains and ditches may be required on long cut and fill slopes. c. Interceptor/diversion ditches should be constructed to prevent surface runoff water from running over and down the sides of cut backslopes. Roadbed shoulders should be shaped to their original design configuration to the extent possible to ensure uniform runoff. d. There are several methods of erosion control, including re-grading of slopes, flattening of slopes, using variations of seeding and sodding, the use of layers of coarser materials, and vegetative matting. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-65 Roadway and Ballast 1.4.5.3 Seeding and Sodding a. Steps in seeding and mulching eroded slopes consist of filling gullies, placing topsoil where required, applying fertilizer, seeding, mulching, and, if required, reseeding until vegetative cover is established. Local state highway standards and specifications can be very helpful sources of information concerning recommended seeding and sodding. Some railroads have their own standards/requirements for seeding, fertilizer, seed mixtures and mulching. Suitable seed mixtures and fertilizers for particular locations can also be recommended by agricultural bureaus. Grasses or ground covers can be used to control erosion. However, ground covers can be killed by chemicals used to control vegetation along the right-of-way. b. The application of seed and fertilizer can be done on flat areas and moderate slopes with a seed drill, and on steep slopes with a hydroseeder. A mulch spreader is used to apply straw tacked with asphalt. Although this mechanical equipment is efficient and economical to use, small eroded areas can commonly be prepared and treated by hand, with substantial benefits. Grass should be cut at least once to thicken the growth. c. Where active erosion of young growth may occur, vegetative matting can be used with seeding, giving good protection against erosion. Seed and fertilizer is applied both under and over the matting, without mulch. The matting should be applied according to the manufacturer’s specified procedures. d. Sod is costly and usually only used on areas where immediate vegetation coverage is required and for aesthetic reasons. Where necessary to prevent slippage on slopes, sod should be pegged in place. Use of light wire netting over the sod can improve stability of the sod layer. 1.4.5.4 Filter Layers a. Earth slopes can also be protected against erosion with a layer of coarser material. In such cases it is essential to distribute surface runoff water and avoid concentrated flows of water from the top to the bottom of the slope. Filling gullies with coarse material will not in itself prevent further erosion. b. A graded filter layer can be used as a maintenance method when water seepage from pervious layers in the slope causes erosion. The filter layer is designed to keep the underlying soil in place while at the same time carrying flow from both seepage and rainfall without eroding itself. The thickness of the layer depends on the intensity of rainfall and on angle of repose of the filter material. A filter layer must be properly designed and installed. Properly installed filter layers can prevent erosion under conditions that would cause seeding or sodding to be an unsuccessful method of slope protection. 1.4.5.5 Filter Fabrics (see Chapter 1, Part 10) a. A geosynthetic layer or filter fabric can be installed to prevent erosion on earth slopes. These porous membranes are available as woven fabric or as thin fibrous mats. In either form they are designed to be fine enough to hold the slope soil material in place, but porous enough to allow passage of seepage water. b. The performance of filter fabrics is often superior to that of filter layers as they have a built-in filtering capability which does not depend on field workmanship. Detailed installation procedures are available from manufacturers. Generally, the slope to be protected must be uniform and gullies and holes filled. The fabric is spread loosely on the slope, with proper overlapping and sheets pinned in place. A layer of random gravel or crushed stone is placed immediately on top of the fabric to keep it in place, working from the base of slope upward. This fabric must have sufficient puncture resistance and strength to avoid damage by either of the techniques used for placement of gravel/stone or future erosion. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-66 AREMA Manual for Railway Engineering Roadbed 1.4.6 METHODS OF OPENING SNOW BLOCKADES (2007) 1.4.6.1 General a. Keeping a railway line open in territory subject to heavy snow requires watchfulness, orderliness and forethought. In the fall of the year all snow equipment and accessories should be tested and made ready for use. A general program should be formulated for stationing snow-fighting equipment at vantage points, outlining a general supervisory plan, and determining methods by which men are to be secured, protected from hazards attending snow storms, fed and relieved. b. Where such reports are considered helpful, meteorological information should be made available for general and division officers and local officers should be kept well informed of the progress of approaching storms. c. It is desirable to keep ahead of storms and not let the line become blocked. In some areas best results are obtained when snow plows are started from terminals before the storm actually breaks and, in severe storms, additional plows dispatched at such intervals as will preclude the formation of snow banks that cannot be moved with plows. A follow-up locomotive to pull out the plow or its engine, or both, if they get stalled or derailed, is good practice when conditions warrant. Prompt clearance of cuts before further snow or wind storms is important. Secondary storms often cause the greatest problems. d. During severe storms, if there is difficulty in keeping the line open, consideration should be given to reducing tonnage, double heading or the abandonment of trains and curtailment or complete stopping of yard switching until the storm abates and the line is opened. Stalled trains and dead locomotives add much expense, anxiety and hazard to the work of moving snow and delay the opening of blockades. e. No definite rule can be established for the use of flangers or plows. Much depends on the moisture content of the snow, the formation of drifts, and on the available clear space for snow disposal. 1 1.4.6.2 On Line a. Flangers should be used for the removal of snow where the depth is less than 6 inches over the top of the rail. Flanging of tracks is greatly expedited if the flanger is equipped with scoops for each direction, which allow flangeways to be cleared in either direction without turning the flanger. The scoops must in all cases be equipped with lowering and raising device operated from inside the car. A flanger may frequently be used to good advantage by attaching it to the rear of a freight train and thus avoid using an extra train and crew. b. The wedge or snow plow placed on the pilot of the locomotive is useful for occasional light drifts of up to 2 or 3 feet over the top of the rail, if state laws permit such operation. c. The larger wedge or snow plow should be used for removing snow up to 6 or 8 feet deep which cannot be removed by flangers or push plows on locomotive pilots. The effectiveness of these plows is greatly increased if they are equipped with adjustable side wings, which can be used for widening the opening. These plows should be equipped with a coupler on the front and rear to expedite the switching of cars off of siding or yard tracks which must be cleared of snow. Means of communication by telephone or signals between crew and plow operator expedite this operation. d. Great care must be exercised in the use of plows placed on the front of loaded ballast or gondola cars to prevent the weight of the snow on the cutting edge of plow from riding on the rail and catching at frogs, switches and crossing plank. This can be prevented by a narrow casting placed under the plow near the cutting edge so as to ride on the rail and keep the plow up. Special consideration must be given the designating and placing of this casting if self-guarded frogs are to be encountered. There are combined flangers and plows so designed that this problem does not occur. e. Care must be taken when entering oblique snow drifts that do not allow the plows to strike the snow squarely - as such conditions sometimes result in the plow turning over. The face of a drift should be broken down or “faced” so that the plow will engage the snow and not ride atop the drift. If the plow has © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-67 3 4 Roadway and Ballast been stuck and pulled back, the snow may have been compacted to such an extent that it should be broken down before making another charge and possibly causing serious damage to the plow from impact with the solid snow. f. Spreaders or spreader ditchers with a plow-shaped front make excellent snow movers. The spreader wings can be used to good advantage to widen the cut after it is opened up. Many of these ditchers are equipped with steel teeth (set under the front edge of the plow) which are very effective in cutting up ice which may have formed between and over the rails. g. Ice cutter cars have been used with great effectiveness for loosening hard snow and ice which form in the tracks, especially in yards, and on occasions in many miles of tracks. These cars are essentially box cars with end lookout windows, and with compressed air equipment by means of which a lever may be moved to raise and lower a plow or V-shaped steel plate, 1 inch thick, 6 inches wide, and about 4’- 9" long, placed below the center of the car on edge and between the running rails. To this steel plate, 4 inches apart and extending 6 inches below its lower edge, are bolted tire-steel teeth with points inclined slightly forward. Extra teeth are carried in the car. The cutter must, of course, be raised at turnouts and crossings. h. Rotary snow plows are necessary for the quick removal of snow where the snowfall has filled deep cuts which cannot be removed with push plow. Attempts to use them in shallow drifts not deep enough for reasonably full contact of the wheel may cause the wheel to race under the light load and damage the machinery. i. When operating flangers and plows over the line, the problem of keeping ice and snow out of guard rails, frogs and switches is important, particularly in locations which are difficult for maintenance forces to get to in severe storms. De-icing chemical can be used, but attention should be given to problems they can create in electrified, automatic signal, or train-control territory. 1.4.6.3 In Yards and Terminals a. The method for removal of snow from yards and terminals depends upon the physical layout, the density of traffic, and the amount of snow. If snow is not very deep, it is best not to remove it from the tracks, except to make flangeways by hand shoveling, or with flangers if traffic will permit, and clean out of switches by hand with shovels, brooms, or use of snow blowers or snow melters. Removal operations should avoid blowing snow back over places already cleaned. The use of melters requires good drainage to carry away melted snow as it may freeze and cause more trouble than the snow. Otherwise the heat must be great enough to evaporate the water. Because of its potential to increase corrosion and electrical conductivity, salt should be used sparingly. If possible, it should not be used in electrified, automatic signal or train-control districts and should be used in other districts only during that portion of winter when snow melts during the daytime and freezes at night. Salt may be used in some instances to prevent slippery conditions in the area of the switch stand. b. In clearing yard tracks of heavier falls of snow, it is well first to pull cars off of four tracks; then run a plow down one track and follow with a spreader, pushing the snow clear of adjacent tracks; then run the spreader down the cleared tracks, repeating the operation until the snow is piled too high for further piling. The clearing should then start on the other side of the pile and repeat. In some instances, where the yard is not too wide and the snow not too heavy, the entire yard may be cleared with the spreader; thus picking up of the snow is avoided. Where this cannot be done, the piles of snow must be left to melt or be mechanically loaded onto cars. c. In cleaning snow off station platforms, where snowfall is light, hand methods are probably the most economical. Use of brooms and snow shovels are effective. Snow should not be placed on tracks, as passing trains may throw it onto platforms. Hand-operated power snow plows or farm tractor-type plows are useful for platform cleaning. A supply of de-icer, salt, or sand should be on hand at stations to scatter over platforms in sleeting and freezing weather. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-68 AREMA Manual for Railway Engineering Roadbed d. At team yards snow can be pushed to the center or side of driveway with plows placed on trucks or tractors. The snow may be left to melt or loaded onto trucks or cars by hand or machinery. Front-end loaders are useful in this operation. e. Jet snow blowers on track equipment, revolving brooms attached to small tractors, and flangeway cleaners attached to motor cars are other devices that have been found useful in cleaning crossings, yard leads, etc. 1 3 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-1-69 Roadway and Ballast THIS PAGE INTENTIONALLY LEFT BLANK. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-1-70 AREMA Manual for Railway Engineering 1arema Part 2 Ballast1 — 1997 — FOREWORD In the early days of the U.S. Railroad Industry, a variety of materials were used for track ballast to support the track superstructure. Almost any ballast material which could be procured on line at a low unit cost was used and considered satisfactory under the traffic loadings. As rail loadings and speed increased, track geometry deterioration became a problem for the industry. Track geometric deviations and rail wear were recognized as major maintenance problems in the early teens. This resulted in the organization of a special joint committee sponsored by the AREMA and A.S.C.E. to study stress in the railroad track structure under the chairmanship of Professor A. N. Talbot. The committee immediately began their study of the track superstructure support, i.e. rails, cross ties, and fastenings. The study produced the “U” value as a measurement of vertical track stiffness as defined in the AREMA Bulletin, Volume 19, Number 205, March, 1918. The “U” value represents the stiffness of the track and involves conditions of the ties, ballast and roadway. Study of “U” values in the superstructure indicated that the influences of the track substructure (ballast and sub-ballast) were significant. Thus the need for better ballast materials became more obvious. Extensive ballast material tests were conducted by Rockwell Smith of the AREMA during the middle fifties and sixties. The test results indicated that the ballast was an integral part of the track substructure and that support in the roadbed section has a direct relationship to the quality of the ballast materials. Today greater demands are placed on the track superstructure and substructure. Heavier wheel loads, higher operating speeds and unit train consists demand better total performance of the track system. The improvement of the performance of the substructure appears to be an economical approach to increasing the strength of the track system. More emphasis must be placed on the quality and type of ballast materials used in the substructure. Improved geotechnical techniques and test methods together with a better understanding of soils have provided the opportunity for ongoing tests to evaluate the quality and support characteristics of ballast materials. 1 References, Vol. 5, 1904, pp. 487, 502; Vol. 6, 1905, pp. 737, 745; Vol. 11, 1910, part 2, pp. 907, 930; Vol. 13, 1912, pp. 97, 949; Vol. 16, 1915, pp. 1007, 1159; Vol. 22, 1921, pp. 80, 958; Vol. 26, 1925, pp. 439, 1311; Vol. 31, 1930, pp. 768, 1740; Vol. 32, 1931, pp. 101, 731; Vol. 33, 1932, pp. 355, 798; Vol. 37, 1936, pp. 560, 575, 980, 987; Vol. 38, 1937, pp. 191, 621; Vol. 42, 1941, pp. 573, 831; Vol. 45, 1944, pp. 312, 637; Vol. 54, 1953, pp. 1092, 1385; Vol. 60, 1959, pp. 710, 1184; Vol. 63, 1962, pp. 576, 749; Vol. 65, 1964, pp. 504, 837; Vol. 67, 1966, pp. 539, 740; Vol. 76, 1975, p. 145; Vol. 78, 1977, p. 10: Vol. 87, 1986, p. 38; Vol. 89. 1988, pp. 40, 48, 58; Vol. 92, 1991, p. 35; Vol. 97, p. 20. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-2-1 1 3 Roadway and Ballast During the past twenty year period, extensive ballast material tests have been conducted by the railroad industry, the railway supply industry, universities and some governmental agencies. This includes the ballast and roadway tests at TTCI (formerly FAST facility). From the results of these multiple material tests and performance evaluations, improved information has been obtained on the desirable physical and chemical properties of ballast materials which will provide performance characteristics commensurate with current track loadings and cost effective maintenance requirements of the track substructure. The following Ballast Specification is the first general revision of the AREMA Ballast Specification in over forty years. The Specification is the result of the aforementioned test data obtained in the laboratory, field testing, and the actual performance evaluation of various ballast materials in track. The efforts to produce a definitive ballast performance specification are not complete. A laboratory test to simulate performance and evaluation of ballast materials in track has not been developed. However; ongoing current ballast tests dedicated to the correlation of laboratory tests to field performance indicate that we may be approaching our goal. The results of these testing programs could dictate further improvement of the Ballast Specification in the future. TABLE OF CONTENTS Section/Article Description Page 2.0 Substructure Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0.1 Description (1991) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0.2 Nomenclature (1991) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-4 1-2-4 1-2-4 2.1 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.1 Track Substructure Design (1991) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-5 1-2-5 2.2 Scope (1991) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-9 2.3 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1 Types of Materials (1991) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-9 1-2-9 2.4 Property Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.1 Physical Analysis (1991). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.2 Chemical Analysis (1988) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.3 Limiting Test Values (1997) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.4 Gradations (1988) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.5 Ballast Materials for Concrete Tie Track Installation (1988) . . . . . . . . . . . . . . . . . . . . . . 1-2-10 1-2-10 1-2-11 1-2-11 1-2-12 1-2-12 2.5 Production and Handling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.1 General (1988) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-13 1-2-13 2.6 Loading (1988) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-13 2.7 Inspection (1988) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-14 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-2-2 AREMA Manual for Railway Engineering Ballast TABLE OF CONTENTS (CONT) Section/Article Description Page 2.8 Sampling and Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.8.1 General (1988) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-14 1-2-14 2.9 Measurement and Payment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.9.1 General (1988) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-15 1-2-15 2.10 Maintenance Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.10.1 Methods of Unloading and Distributing Ballast (1988) . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.10.2 Replacement of Ballast and In-Track Cleaning (1988) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.10.3 Commentary (1988). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.10.4 Ballast Gradations (1988) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-15 1-2-15 1-2-15 1-2-15 1-2-18 2.11 Sub-ballast Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.11.1 General (1996) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.11.2 Design (1996) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.11.3 Testing (1996) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.11.4 Construction of Sub-ballast Section (1996) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.11.5 Production and Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.11.6 Inspection (1996) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.11.7 Measurement and Payment (1996) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-19 1-2-19 1-2-20 1-2-24 1-2-24 1-2-24 1-2-25 1-2-25 Commentary (1988) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-25 Summary (1988). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-26 3 LIST OF FIGURES Figure 1-2-1 1-2-2 1-2-3 1-2-4 1-2-5 Description Typical Section Track Substructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Single Track, Superelevated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multiple Track, Tangent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multiple Track, Superelevated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example Using Table 1-2-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 1-2-6 1-2-6 1-2-7 1-2-7 1-2-23 LIST OF TABLES Table 1-2-1 1-2-2 1-2-3 1-2-4 Description Recommended Limiting Values of Testing for Ballast Material . . . . . . . . . . . . . . . . . . . . . . . . . Recommended Ballast Gradations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Requirements for Filter Material (after USBR1963) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sub-ballast Properties and Test Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 1-2-12 1-2-13 1-2-23 1-2-24 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1 1-2-3 4 Roadway and Ballast SECTION 2.0 SUBSTRUCTURE INTRODUCTION 2.0.1 DESCRIPTION (1991) This part of these Specifications shall cover the design, materials, evaluation, production, construction and maintenance and evaluation of those components of the track structure which are situated above the soils or rock of the roadbed, or the wood, steel or concrete materials of the roadbed, installed for the purpose of providing support to the rail-cross tie arrangement of a conventionally constructed track system. 2.0.2 NOMENCLATURE (1991) Within these specifications, the following terms shall be defined as: a. Track Superstructure. The assembly of rail, cross ties, other track materials and special track materials which are the components of a conventionally constructed track system. b. Track Substructure. The strata of granular materials that are installed for the purpose of: (1) Permitting drainage within the track substructure. (2) Anchorage of the track superstructure in the three dimensions of space. (3) Distribution of loads and transfer of the track superstructure loads to the underlying roadbed. (4) Facilitating fine adjustment of track superstructure alignment, grade and cross level without system reconstruction. (5) Shielding the materials of the roadbed from climatic forces. c. Ballast. The upper stratum of the substructure upon which the superstructure is placed to a depth as defined by the individual railway company standards. d. Sub-ballast. A lower stratum of the substructure beneath the ballast section located upon the roadbed to a depth as defined by the individual railway company standards. e. Roadbed. The stratum of soil or rock which is constructed in accordance with Part 1, Roadbed which provides support for the track structure. NOTE: Except for new construction, the boundaries between the strata, as defined, may not be distinct. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-2-4 AREMA Manual for Railway Engineering Ballast SECTION 2.1 DESIGN 2.1.1 TRACK SUBSTRUCTURE DESIGN (1991) 2.1.1.1 Description This section of these specifications will discuss the cross sections of the track substructure components, the ballast and sub-ballast sections. Single and multiple track construction will be addressed, as will track with superelevation. The following figures are shown: • Figure 1-2-1 Typical Section Track Substructure • Figure 1-2-2 Single Track, Superelevated • Figure 1-2-3 Multiple Track, Tangent • Figure 1-2-4 Multiple Track, Superelevated 2.1.1.2 Variables of Design The variables to be considered in establishing the dimensions of a track substructure are noted below and shown on Figure 1-2-1. The variables of the track superstructure which effect the design of the substructure are first noted. 1 2.1.1.2.1 For the Track Superstructure • TRG = The Track Gage. • TSE = The Superelevation of the Track. • TTH = The Thickness of the Cross Tie. 3 • TLE = The Length of the Cross Tie. • TWD = The Width of the Cross Tie. • TSP = The Spacing of Cross Ties, center to center. 4 • The variables TRO, TTH, TLE, TWD and TSP are not shown on the figures. 2.1.1.2.2 For the Track Substructure 2.1.1.2.2.1 Ballast Section • BDD = The Ballast Section Depth. • BSW = The Ballast Section Shoulder Width. • BSS = The Side Slope Run component of the Ballast Section in a unity rise to run ratio. 2.1.1.2.2.2 Sub-ballast Section • SBD = The Sub-ballast Depth • SBS = The Side Slope Run component of the Sub-ballast Section in a unity rise to run ratio. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-2-5 Roadway and Ballast Figure 1-2-1. Typical Section Track Substructure Figure 1-2-2. Single Track, Superelevated 2.1.1.2.2.3 Roadbed • RSW = The Roadbed Shoulder Width. • RBR = The Side Slope Run component of the Roadbed Section in a unity rise to run ratio. • RBW = The Roadbed Berm Width. 2.1.1.3 Standards, Design Criteria and Regulation Unless otherwise established by the Standards of Track Construction and as may be defined by individual Railway standards, the Project Design Criteria, or a like document, the following paragraphs of this Part of this Manual shall govern the proportioning of the track substructure components. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-2-6 AREMA Manual for Railway Engineering Ballast Figure 1-2-3. Multiple Track, Tangent 1 3 Figure 1-2-4. Multiple Track, Superelevated 2.1.1.4 Track Superstructure a. The Track Gage (TRG) shall be 56.50 inches, Standard Gage. The Superelevation of Track (TSE) shall be determined in accordance with Chapter 5, Track, Part 3, Curves. b. The Cross Tie Thickness (TTH), Length (TLE), Width (TWD) and the Spacing (TSP) shall be proportioned in accordance with relationships show in Chapter 16, Economics of Railway Engineering and Operations, Part 10, Construction and Maintenance Operations. 2.1.1.5 Track Substructure 2.1.1.5.1 Total Depth of Section (BDD + SBD) The total depth of the track substructure section shall be determined in accordance with the relationships shown in Chapter 16, Economics of Railway Engineering and Operations, Part 10, Construction and Maintenance Operations. The sum of Ballast Section Depth (BDD) and Sub-ballast Depth (SBD) shall equal the calculated total depth of track substructure section. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-2-7 4 Roadway and Ballast 2.1.1.5.2 Ballast Section 2.1.1.5.2.1 Ballast Section Depth (BDD) a. The ballast section is the upper portion of the track substructure section and is constructed of material conforming to Article 2.3.1. b. For single track construction, the measurement BDD is made under the Line Rail in tangent track, or under inside rail in curved track, and is made with respect to the top of the sub-ballast at the center line of track. On tangent multiple track construction, the measurement is made under that rail which is toward the crown of the Sub-ballast Section. On curved multiple track construction, the measurement is made under the rail to the inside of the curve. c. A value for BDD of a minimum of 12 inches is recommended for Standard Gage construction in main track service or as defined by individual railway company standards. 2.1.1.5.2.2 Ballast Section Shoulder Width (BSW) a. The Ballast Section Shoulder Width is proportioned in accordance with Chapter 16, Economics of Railway Engineering and Operations, Part 10, Construction and Maintenance Operations and is to provide additional lateral strength to the track. b. The measure is made from the end of the cross tie to the point of beginning of the Ballast Side Slope (BSS), and is made in the plane of the top of the cross tie. c. A value for BSW of not less than 12 inches is recommended for Standard Gage construction of continuous welded rail in main track service or as may be defined by individual railway company standards. 2.1.1.5.2.3 Side Slope (BSS) a. The Side Slope run component of the Ballast Section is proportioned to provide confining pressure to that part of the Ballast Section expected to transmit the vertical load from the bottom of the cross tie to the top of the sub-ballast. b. The BSS run component is measured in the plane of the top of the cross tie, and the rise component is measured perpendicular to the run component. c. A BSS value of 2:1 is commonly used. 2.1.1.5.3 Sub-ballast 2.1.1.5.3.1 Sub-ballast Depth (SBD) a. The sub-ballast is the lower section of the track substructure and is constructed in accordance with the specifications contained in Section 2.11, Sub-ballast Specifications. b. The depth measured is made with respect to the top of the Roadbed. c. A value for SBD of 12 inches compacted is commonly used for Standard Gage construction in main track service. A minimum value of 6 inches compacted is considered necessary to perform the separation of layers and shielding of the roadbed from weather functions. 2.1.1.5.3.2 Side Slope (SBS) a. The Side Slope run component of the Sub-ballast Section is proportioned to provide drainage from the top of the roadbed construction. b. A value for SBS of not less than 24 or more than 40 is recommended. Sub-ballast materials having relatively lower permeability rates may use relatively higher SBS values. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-2-8 AREMA Manual for Railway Engineering Ballast 2.1.1.6 Roadbed The Roadbed Shoulder Width (RSW), Side Slope Run component of the Roadbed (RBR), and Roadbed Berm Width (RBW) shall be established in accordance with principals and recommendations contained in Part 1, Roadbed. SECTION 2.2 SCOPE (1991) a. These specifications cover the types, characteristics, property requirements and manufacture of mineral aggregates for processed (prepared) ballast. Ideally processed ballast should be hard, dense, of an angular particle structure providing sharp corners and cubical fragments and free of deleterious materials. Ballast materials should provide high resistance to temperature changes, chemical attack, have high electrical resistance, low absorption properties and be free of cementing characteristics. Materials should have sufficient unit weight (measured in pounds per cubic foot) and have a limited amount of flat and elongated particles. b. The type or types and gradations of processed ballast materials as covered in these specifications and testing requirements shall govern the acceptance or rejection of ballast materials by the Engineer, or as directed by the individual railway company. 1 SECTION 2.3 MATERIALS 2.3.1 TYPES OF MATERIALS (1991) a. A variety of materials may be processed into railroad ballast. The following general classifications and accompanying definitions list the most common materials. Detailed examination of individual materials should be made to determine the specific mineralogical composition. 3 b. Granite is a plutonic rock having an even texture and consisting chiefly of feldspar and quartz. Definitions: A plutonic rock is rock formed at considerable depth by chemical alteration. It is characteristically medium to coarse grained, or granitoid texture. c. 4 Traprock is any dark-colored fine grained non-granitic hypabyssal or extrusive rock. Definitions: Hypabyssal – Pertaining to igneous intrusion or to the rock of that intrusion whose depth is intermediate between that of plutonic and the surface. d. Quartzite is a granoblastic metamorphic rock consisting mainly of quartz and formed by recrystallization of sandstone or chert by either regional or thermal metamorphism. Quartzite may also be a very hard but unmetamorphosed sandstone, consisting chiefly of quartz grains with secondary silica that the rock breaks across or through the grains rather than around them. Definitions: Granoblastic – type of texture is a nonschistose metamorphic rock upon which recrystallization formed essentially equidimensional crystals with normally well sutured boundaries. Chert-A hard, dense cryptocrystalline sedimentary rock consisting dominantly of interlocking crystals of quartz. e. Carbonate rocks are sedimentary rocks consisting primarily of carbonate materials such as limestone and dolomite. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-2-9 Roadway and Ballast f. Slags are materials formed during the metal making process by the fusion of fluxstones, coke and other metallic particles and are generally of two types; iron blast furnace slag and steel furnace slag. Iron blast furnace slag is produced during the blast furnace operation and is essentially a composition of silicates and alumino silicates of lime and other bases. Steel furnace slag is a by-product of the open hearth, electric or oxygen steel furnace and is composed primarily of oxides and silicates. SECTION 2.4 PROPERTY REQUIREMENTS 2.4.1 PHYSICAL ANALYSIS (1991) The methods of sampling and testing as defined by this specification are those in effect April 1985 and may be revised or altered by the individual railway company. 2.4.1.1 Method of Sampling Field samples shall be secured in accordance with the current ASTM Methods of Sampling, designation D 75. Test samples shall be reduced from field samples by the means of ASTM C 702. 2.4.1.2 Sieve Analysis Sieve analysis shall be made in accordance with ASTM Method of Test, designation C 136. 2.4.1.3 Material Finer Than No. 200 Sieve Material finer than the No. 200 sieve shall be determined in accordance with the ASTM Method of Test, designation C 117. 2.4.1.4 Bulk Specific Gravity and Absorption The bulk specific gravity and percentage of absorption shall be determined in accordance with the ASTM Method of Test, designation C 127. 2.4.1.5 Percentage of Clay Lumps and Friable Particles The percentage of clay lumps and friable particles shall be determined in accordance with the ASTM Method of Test, designation C 142. 2.4.1.6 Resistance to Degradation The resistance to degradation shall be determined in accordance with the ASTM Method of Test, designation C 131 or C 535 using the grading as specified in Note # 1, Table 1-2-1. Materials having gradations containing particles retained on the 1 inch sieve shall be tested by ASTM C 535. Materials having gradations with 100% passing the 1 inch sieve shall be tested by ASTM C 131. 2.4.1.7 Sodium Sulfate Soundness Sodium Sulfate Soundness tests shall be made in accordance with the ASTM Method of Test, designation C 88. 2.4.1.8 Unit Weight The weight per cubic foot shall be determined in accordance with the ASTM Method of Test, designation C 29. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-2-10 AREMA Manual for Railway Engineering Ballast 2.4.1.9 Percent of Flat and/or Elongated Particles The percent of flat or elongated particles shall be determined in accordance with ASTM Standard Test Method, designated D4791. The dimension ratio used in this test method shall be 1:3. 2.4.2 CHEMICAL ANALYSIS (1988) a. No specific chemical analysis is considered essential for the evaluation of granite, traprocks or quartzite type materials provided that the materials are properly defined by applicable methods. For carbonate materials, dolomitic limestones are defined as those materials which have a magnesium carbonate (MgCo3) content of 28% to 36%. Those carbonate materials indicating magnesium carbonate values above 36% shall be defined as dolomites and carbonate materials indicating magnesium carbonate values below 28% shall be defined as limestones. b. The magnesium carbonate (MgCo3) content of carbonate materials shall be tested and defined in accordance with ASTM C 25. c. Standard Methods of Chemical Analysis of Limestone, Quick Lime and Hydrated Lime, or other test methods as may be approved and directed by the Engineer. d. Steel furnace slags consist essentially of calcium silicates and ferrites combined with fused oxides of iron, aluminum, manganese, calcium and magnesium. e. Steel furnace slags having a content of more than 45% calcium oxide and/or a combined composition of more than 30% of the oxides of iron and aluminum should not be used. f. Iron blast furnace slags consist essentially of silicates and aluminosilicates of calcium and other bases. g. Iron blast furnace slags having a content of more than 45% of the oxides of calcium or a combined composition of more than 17% of the oxides of iron and aluminum should not be used. 1 3 2.4.3 LIMITING TEST VALUES (1997) Table 1-2-1 outlines the limiting values of testing as may be defined by the designated test specifications. The values for unit weight and bulk specific gravity are minimum values while the remainder are maximum values. Table 1-2-1. Recommended Limiting Values of Testing for Ballast Material 4 Ballast Material Property Granite Traprock Quartzite Limestone Blast Dolomitic Furnace Limestone Slag Steel Furnace Slag ASTM Test Percent Material Passing No. 200 Sieve 1.0% 1.0% 1.0% 1.0% 1.0% 1.0% 1.0% C 117 Bulk Specific Gravity (See Note 2) 2.60 2.60 2.60 2.60 2.65 2.30 2.90 C 127 Absorption Percent 1.0 1.0 1.0 2.0 2.0 5.0 2.0 C 127 0.5% 0.5% 0.5% 0.5% 0.5% 0.5% 0.5% C 142 Clay Lumps and Friable Particles © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-2-11 Roadway and Ballast Table 1-2-1. Recommended Limiting Values of Testing for Ballast Material Ballast Material Property Granite Traprock Quartzite Limestone Blast Dolomitic Furnace Limestone Slag Steel Furnace Slag ASTM Test Degradation 35% 25% 30% 30% 30% 40% 30% See Note 1 Soundness (Sodium Sulfate) 5 Cycles 5.0% 5.0% 5.0% 5.0% 5.0% 5.0% 5.0% C 88 Flat and/or Elongated Particles 5.0% 5.0% 5.0% 5.0% 5.0% 5.0% 5.0% D 4791 Note 1: Materials having gradations containing particles retained on the 1 inch sieve shall be tested by ASTM C 535. Materials having gradations with 100% passing the 1 inch sieve shall be tested by ASTM C 131. Use grading most representative of ballast material gradation. Note 2: The limit for bulk specific gravity is a minimum value. Limits for the remainder of the tests are maximum values. 2.4.4 GRADATIONS (1988) Table 1-2-2 outlines the recommended gradations to which the materials are to be processed for use as track and yard ballast. The grading of the processed ballast shall be determined with laboratory sieves having square openings conforming to ASTM specification E 11. 2.4.5 BALLAST MATERIALS FOR CONCRETE TIE TRACK INSTALLATION (1988) The ballast materials as defined by this specification include the applicable test requirements for ballast materials for the purpose of providing support to the rail-cross tie arrangement of a concrete tie track system except that carbonate materials and slags as defined in Article 2.3.1 and gradation No. 57 as defined in Article 2.4.4 shall be excluded. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-2-12 AREMA Manual for Railway Engineering Ballast Table 1-2-2. Recommended Ballast Gradations Size No. (See Note 1) Nominal Size Square Opening Percent Passing 3 2½ 2 1½ 24 2½ - ¾ 100 90-100 25-60 25 2½ - d 100 80-100 60-85 50-70 3 2 - 1 – 100 4A 2 - ¾ – 100 – – 100 4 1½ - ¾ 1 ¾ 0-10 ½ d No.4 No. 8 0-5 – – – 25-50 – 5-20 0-10 0-3 – 95-100 35-70 0-15 – 0-5 – – – 90-100 60-90 10-35 0-10 – 0-3 – – 90-100 20-55 0-15 – 0-5 – – 5 1 - d – – – 100 90-100 40-75 15-35 0-15 0-5 – 57 1 - No. 4 – – – 100 95-100 25-60 – 0-10 0-5 – Note 1: Gradation Numbers 24, 25, 3, 4A and 4 are main line ballast materials. Gradation Numbers 5 and 57 are yard ballast materials. SECTION 2.5 PRODUCTION AND HANDLING 1 2.5.1 GENERAL (1988) a. The aggregate production facility shall be of such a design to permit production and or blending without excessive working of the materials and the facility must be approved by the purchaser. The capacity of the production facility should be adequate to efficiently produce the anticipated daily loadings providing sufficient stockpiles to facilitate loadings without any delays. b. Blending, stockpiling and other production and handling operations shall be managed by the producer to minimize segregation of the finished product. Stockpiling operations shall minimize as practical the breakage or excessive fall in stockpiling operations and the movement of wheeled or tracked machines over stockpiled materials shall be limited. c. Processed ballast shall be washed and/or rescreened as necessary to remove fine particle contamination as defined by the specification or as directed by the individual railway company prior to stockpiling in operations using stockpiles or immediately prior to loading operations. SECTION 2.6 LOADING (1988) a. The manufacturer shall arrange the required supply of railcars, unless the purchase arrangement provides otherwise. The manufacturer shall assure the fitness of the cars for loading of the prepared materials, arranging to clean cars of deleterious materials, plug leaks and other like operations, as necessary. b. Unless otherwise specified, rail cars shall be ballast cars furnished by the purchaser or hopper-type, or as designated by the Engineer. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-2-13 3 4 Roadway and Ballast SECTION 2.7 INSPECTION (1988) a. The railway company, or its representatives, reserve the right to visit the producers facility during usual business hours unscheduled for the following purposes: (1) Observe sampling and testing procedures to assure compliance with the requirements of these specifications. (2) Obtain representative samples of the prepared material being produced and shipped. (3) Review plant inspection, methods, quality control procedures, equipment and examine test results of current and previous tests. b. The manufacturer shall provide the inspector with such assistance, materials, and laboratory testing equipment as necessary to perform on production site gradation and percent passing No. 200 Mesh Sieve analysis. Performance of these tests at the time of an unscheduled inspection visit is the right, but not the duty, of the inspector. SECTION 2.8 SAMPLING AND TESTING 2.8.1 GENERAL (1988) a. The quality of a material to be used for ballast shall be determined prior to its acceptance by the purchaser. A series of tests as specified herein shall be made at a testing laboratory approved by the purchaser to establish the characteristics of the materials being tested. b. Once a source has been accepted to supply ballast material, periodic quality control samples shall be taken to insure continued compliance with the specification. A representative sample of prepared ballast shall be taken for gradation from each 1000 tons of ballast being loaded for shipment. This sample shall be taken in accordance with ASTM D 75, and in the quantities as listed within that standard. A gradation report shall be prepared on each sample containing the following information: Source identification, date, sample number, shipment or car number, and the sieve analysis. The gradation specification shall appear on the test form. c. In the event any two individual samples fail to meet the gradation requirement, immediate corrective action shall be taken to restore the production process to acceptable quality. The purchaser shall be advised in writing of the corrective action being taken. In the event of repeated failures, i.e. two or more samples failing in two successive shipments, the purchaser reserves the right to reject the shipment. d. A full range of laboratory testing, as defined by this specification, shall be performed at least two times a year or as directed by the Engineer, to insure the quality of the material being produced. If the supplier changes the location of the source or encounters changes within the supply source, laboratory testing should be performed on the new material to ensure compliance with specifications. e. Prior to installation, the supplier shall provide the Engineer with certified results of ballast quality and gradation as conducted by a testing laboratory accepted by the Engineer. The supplier shall receive approval of the Engineer for the Testing Laboratory prior to performing the aforementioned tests. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-2-14 AREMA Manual for Railway Engineering Ballast SECTION 2.9 MEASUREMENT AND PAYMENT 2.9.1 GENERAL (1988) a. Ballast shall be measured on a per ton basis and payment shall be made on the number of tons of acceptable materials furnished. No allowance will be made for moisture content of ballast materials loaded by any acceptable method. Weight tickets or records shall be maintained for a period of not less than six months for reference. b. The number of tons shall be determined by one of the following methods and shall be approved by the purchaser: (1) Certified scale weights as determined by track scales (static or in motion weighing) truck scales or belt scales which load directly into the railcar. (2) Average weight agreements as mutually agreed upon by the purchaser and producer. The average net weight for each type and series of railcars shall be determined by the purchaser and producer to establish the average weight agreement per car. The average weight in the specified or type of cars shall be checked quarterly by the purchaser or as designated by the Engineer. The average weight will be calculated on lots of not less than ten (10) cars. The purchaser shall advise the producer if there is any variance in the average weight of the cars selected. The purchaser and the supplier will jointly make any changes in the loading methods to insure compliance with the weight agreement. SECTION 2.10 MAINTENANCE PRACTICES 1 2.10.1 METHODS OF UNLOADING AND DISTRIBUTING BALLAST (1988) Ballast shall be unloaded and distributed as outlined in the Chapter 16, Economics of Railway Engineering and Operations, Part 10, Construction and Maintenance Operations or as defined by individual railway company standards. 3 2.10.2 REPLACEMENT OF BALLAST AND IN-TRACK CLEANING (1988) Replacement of ballast and cleaning shall be performed in accordance with the Chapter 16, Economics of Railway Engineering and Operations, Part 10, Construction and Maintenance Operations or as defined by individual railway company standards. 4 2.10.3 COMMENTARY (1988) a. Ballast is a selected crushed and graded aggregate material which is placed upon the railroad roadbed for the purpose of providing drainage, stability, flexibility, uniform support for the rail and ties and distribution of the track loadings to the subgrade and facilitating maintenance. There are distinct differences in the mineral composition of the various aggregate materials used for roadway ballast applications and the respective in track performance of those materials. Likewise, many variations exist in the mineral properties of aggregate materials within the same general nomenclature of the aggregates known as granites, traprocks, quartzites, dolomites, and limestones. One particular aggregate material may possess most of the desirable characteristics for a good ballast material while a deposit of apparently similar material located in the same general geographical area will not meet the applicable specification requirements for railroad ballast. b. Thus, when selecting ballast materials it is necessary to define the type of material and the physical and chemical properties which can be measured in the laboratory by specific test methods. It is also most important to consider the field performance and behavioral characteristics of the ballast material in the © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-2-15 Roadway and Ballast roadbed section. Some of the properties which affect the field performance of ballast materials can be related to the crushing characteristics, hardness, durability, weight and other physical and chemical properties which are defined in the specification. c. High standards must be established for railroad ballast to provide a quality track structure. Likewise, ballast required for concrete tie installations must exhibit some different behavioral and performance characteristics than those ballast materials which will provide satisfactory field performance for wood tie installations. Ballast is an integral part of the roadbed structure. The ballast section must react to track loadings in combination with the superstructure and sub-ballast to provide supporting strength for the track and roadbed commensurate with specific railroad loadings and operating requirements. d. To provide track stability, the ballast must perform several well defined functions. The ballast must sustain and transmit static and dynamic loads in three directions (transverse, vertical and longitudinal) and distribute those loads uniformly over the subgrade. A prime function of the ballast is to drain the track system. The ballast must also perform a maintenance function to provide proper track alignment, cross level, and grade. e. The most commonly used ballast materials today on the U.S. railroads are granites, traprocks, quartzites, limestones, dolomites and slags, which are defined in the specification. The specification does not limit the use of any rock type which can be processed into ballast when the material is properly defined and tested in accordance with the specifications and is approved by the engineer or purchaser. It is necessary; however, to warn the engineer that materials which tend to create fines will fill the voids between the particles and could inhibit drainage. Some of the powdery fines of carbonate materials have a tendency to cement together and a clogging action could occur. f. The preferred ballast materials would be a clean and graded crushed stone aggregate and/or processed slag with a hard, dense, angular particle structure providing sharp corners and cubicle fragments with a minimum of flat and elongated pieces. These qualities will provide for proper drainage of the ballast section. The angular material will provide interlocking qualities which will grip the ties more firmly to prevent movement. Flat and elongated particles in excess of the maximum as specified in the specification could restrict proper consolidation of the ballast section. The ballast must have high wear and abrasive qualities to withstand the impact of traffic loads without excessive degradation. The stability of the ballast section is directly related to the internal shearing strength of the assembly of ballast particles. The material must possess sufficient unit weight (measured in pounds per cubic foot) as set out in the specification to provide a stable ballast section. The ballast must also provide high resistance to temperature changes, chemical attack, exhibit a high electrical resistance and low absorption properties. A ballast material should be free of cementing properties. Deterioration of the ballast particles should not induce cementing together of the degraded particles. Cementing reduces drainage capabilities, reduces resiliency, and provides undesirable distribution of track loads and in most instances results in permanent track and roadbed deformations. Cementing also interferes with track maintenance. Basically, all ballast materials are placed and tamped in the ballast section in accordance with similar maintenance practices. The materials are then subjected to basic loading patterns, however, there are several factors which will materially affect the in track performance and stability of ballast materials. g. Drainage is the first and prime consideration in the roadbed maintenance and performance of a ballast material. Individual ballast particles must provide a free-draining and clean section for proper drainage of surface water to parallel side ditches or runoff areas. Excessive moisture in subgrades and ballast sections are a primary source of track roadway problems. Side ditches should be free-draining and prevent standing water which could saturate the roadway subgrade. A wet ballast section reduces the shearing strength of the assembly of ballast particles and dirty, moist ballast sections will support the growth of vegetation which reduces the drainage capability of the ballast material. Drainage is a most important factor in contractive and expansive subgrade soil conditions which are prone to cause pumping conditions in the roadbed section. h. Track loading patterns and traffic density, weight of the rail section, grades, the cross section of the ballast section, the sub-ballast and the roadbed interaction together with climatic conditions are major considerations in the performance of ballast materials. A well compacted subgrade and sub-ballast section will provide stable and uniform areas for the distribution of the track loads throughout the ballast section. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-2-16 AREMA Manual for Railway Engineering Ballast i. j. The quality tests as specified in the specification identify several physical properties and characteristics which are desirable for ballast materials. None of the tests considered on an individual basis, however, are indicative of the field performance one might expect from the material. For instance, the test for friable materials (ASTM C 142) identifies materials which are soft and poorly bonded which will result in separate particles being detached from the mass. The test can identify materials which will deteriorate rapidly. Clay in the ballast material is determined by the same test method. Excessive clay can restrict drainage and will promote the growth of vegetation in the ballast section. k. The Sodium Sulfate Soundness Test (ASTM C 88) is conducted with the test sample saturated with a solution of sodium sulfate. This test will appraise the soundness of the aggregate. Materials which do not meet applicable test limits can be expected to deteriorate rapidly from weathering and freezing and thawing. There is some preference for the Magnesium Sulfate Soundness Test, but there is insufficient historical data available for comparison to the Sodium Sulfate Soundness Test which has been used for many years. l. The concentration of fine material below the 200 sieve in the ballast material is determined by the ASTM test method C 117. Excessive fines are produced in some types of crushing and processing operations and could restrict drainage and foul the ballast section. m. The test for flat or elongated particles is determined by ASTM method D 4791 using one of the three dimension ratios. Track stability can be enhanced by eliminating flat or elongated material in excess of the specification by defining a flat or elongated particle as one that has a width to thickness or length to width ratio greater than three. n. Specific gravity and absorption are measured by test method ASTM C 127. Specific gravity in the English measurement system is related to weight and the metric system relates to density. The higher the specific gravity, the heavier the material. A stable ballast material should possess the weight limits as shown in the specification (Test Method ASTM C 29) to provide suitable weight and mass to provide support and alignment to the track structure. Absorption is the measurement of the ability of the material to absorb water. Excessive absorption can result in rapid deterioration during wetting and drying and freezing and thawing cycles. o. The Los Angeles Abrasion Test is a factor in determining the wear characteristics of the ballast material. As directed in the specification, the larger ballast gradations should be tested in accordance with ASTM C 535 while ASTM C 131 is the wear test for smaller gradations. The Los Angeles Abrasion Test relates to the abrasive wear resistance of the aggregate. Excessive abrasion loss of an aggregate will result in reduction of particle size, fouling of the ballast section, reduction of drainage and loss of supporting strength of the ballast section. The Los Angeles Abrasion Test can, however, produce laboratory test results which are not indicative of the field performance of ballast materials. Limestones are primarily calcium carbonate materials with small traces of other minerals. Calcium carbonates are a basic ingredient in the manufacture of cements and degraded carbonate fines have an experience of cementing together in the track structure when degraded particles are produced by track loads imposed upon the track structure and ballast section. p. The performance of granites, traprocks and quartzites differ from that of the limestones when subjected to the same wear and abrasive loading conditions. Granites and traprocks can be coarse-to-fine grained materials and degradation of these materials produces granular fines which do not induce cementing in the roadway. q. The ongoing ballast and roadway tests at TTCI (formerly FAST facility) have also confirmed that the Los Angeles Abrasion Laboratory Test is not indicative of the field performance of ballast materials. r. We must bring to the attention of the engineer that considerable variables exist with many laboratory physical testing methods and procedures and the Los Angeles test is no exception. Not only do variables exist between individual tests, but between testing laboratories as well. Studies conducted by ASTM Committee No. C9 (the committee responsible for the ASTM abrasion test methods and procedures) indicated that for nominal ¾ inch maximum coarse aggregate with percentages of wear in the range of 10% to 45%, the multi-laboratory coefficient of variation is 4.5%. Therefore, the results of two properly © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-2-17 1 3 4 Roadway and Ballast conducted ASTM Los Angeles Abrasion tests from two different laboratories on the same sample of the same coarse aggregate could vary as much as 12.7%. ASTM C 131 defines this variable as a part of the Los Angeles Abrasion Test. s. Likewise, the Sodium Sulfate Soundness Test is not at all precise, particularly in testing limestones. The test results may be affected significantly if the test solution has previously been used to test other carbonate rock samples. The test does provide the opportunity to develop relationships between various materials and will most certainly indicate the presence of shale in carbonate materials. t. The variables in the aforementioned tests and the lack of correlation between the laboratory tests and field performance of ballast material are the prime reasons for ongoing research to develop laboratory tests which are indicative of field performance of ballast materials. The AREMA Ballast Committee is actively pursuing current ballast testing programs in conjunction with the railroads, the A.A.R., T.S.C., FAST and the railroad supply industry to develop laboratory tests to predict field performance. 2.10.4 BALLAST GRADATIONS (1988) a. The gradation of a ballast material is a prime consideration for the in track performance of ballast materials. The gradation must provide the means to develop the compactive or density requirements for the ballast section and provide necessary void space to allow proper run off of ground water. b. Ballast gradations should be graded uniformly from the top limit to the lower limit to provide proper density, uniform support, elasticity and to reduce deformation of the ballast section from repeated track loadings. c. The AREMA mainline ballasts are graded in three sizes from 2½ inches to ¾ inches, 2 inches to 1 inch and 1-1/2 inches to 3₀4 inch; however, two additional gradations No. 25 and No. 4-A have been added to the specification to meet requirements of the railroads. d. Rail yards and some industrial track gradations are generally graded from 1 inch to d inch, (AREMA No. 5 gradation, Table 1-2-2), to provide improved walkway and safety conditions along the track. The finer gradations for yard applications do not restrict track drainage as the construction practices for yard facilities provide quick run off of ground water through the means of under track and yard drainage systems. A consideration in the selection of the proper ballast gradation is the selection of a ballast that will limit the amount of material removed from the track section during undercutting operations. Most undercutting operations remove all of the material below the ¾ inch size. Limiting the amount of the inch material in the original gradation will reduce the amount of ballast removed when undercutting operations are used to clean and restore the track ballast section. The larger ballast gradations being used on the railroads today do not increase the cost of tamping. Mechanization has eliminated most of the necessity for manual labor in the roadway maintenance practices. e. The type of ballast selected for use under concrete ties is a direct function of the track performance with the concrete tie. Extensive field tests of several designs of concrete ties have been installed on various types of ballast materials. The tests concluded that the loading characteristics of the concrete tie are quite different from the loadings imposed on wood ties on the same ballast cross section. Concrete ties which are heavier and less flexible to absorb impact loadings, transmit greater loads to the ballast section and thus create higher crushing loads on the individual ballast particles. Consequently, the selection of ballast materials for concrete ties must be very restrictive to provide satisfactory track performance. Ballast for concrete tie installations must be limited to either crushed granites, traprocks or quartzites. f. A very important consideration is the selection of the proper gradation of the ballast material for concrete ties. The early concrete tie installations were placed on ballast materials graded to the AREMA No. 4 (1½ inches- ¾ inch), resulting in good in track performance, although other ballast materials graded smaller than the AREMA No. 4, Table 1-2-2 gradation did not provide satisfactory support and restraint qualities. Concrete ties placed on ballast gradations smaller than AREMA No. 4 resulted in suspect performance in the first phase of the concrete tie tests conducted at the A.A.R. FAST test facility. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-2-18 AREMA Manual for Railway Engineering Ballast g. Two examples of very good performance of the AREMA No. 4 gradation is the granite ballast used for the concrete tie roadway on the Florida East Coast and the granite ballast used in the concrete tie test installed by the Santa Fe several years ago near Streator, Illinois. h. Concrete ties placed on gradations conforming to AREMA No. 3 (2 inches-1 inch) and AREMA No. 24 (2½ inches- ¾ inch have also exhibited good support qualities and performance characteristics during the second phase roadway tests at TTCI (formerly FAST facility). i. Likewise, ballast graded larger than the AREMA No. 24 gradation has performed well on the northeast corridor concrete tie installations. SECTION 2.11 SUB-BALLAST SPECIFICATIONS 2.11.1 GENERAL (1996) a. This part of the specifications cover design, materials and construction of the sub-ballast section laying between the track ballast and the subgrade as defined in Article 2.0.2d, and composed of a section of smaller dense or well graded granular material. Sub-ballast material is primarily used for the construction of new tracks. b. For over 50 years railroad construction and maintenance practices have utilized a roadway structure for heavy traffic composed of a ballast section approximately 24 inches in depth that included both track ballast and sub-ballast. Experience has indicated a substantial portion of this ballast depth may be successfully composed of a compacted sub-ballast material also serving as a buffer or filter to prevent subgrade material from penetrating the sub-ballast section while at the same time permitting water from whatever source to escape from the area of the subgrade surface. Discussion of the functions of the sub-ballast is provided in the commentary. The engineer must follow established engineering principles for the design, selection of materials and construction of the sub-ballast section of the track substructure. 1 3 2.11.2 DESIGN (1996) a. The railroad substructure must be designed so that the subgrade, sub-ballast and track ballast provide uniform support and distribution of superstructure loadings. The subgrade strength will dictate the combined depth of ballast and sub-ballast materials. b. The following conditions should be considered in the design of the sub-ballast section: (1) Engineering properties of subgrade soil. (2) Support capability of subgrade. (3) Unit load applied to the ballast at the base of tie. (4) Total thickness (track ballast + sub-ballast). (5) Sub-ballast properties. (6) Gradation of sub-ballast. (7) Installation and compaction. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-2-19 4 Roadway and Ballast 2.11.2.1 Subgrade Soils a. The minimum data needed to evaluate the subgrade soils should be classification (which requires Atterberg limits and gradation as appropriate) and strength (lowest expected). The depths and thicknesses of the lower strength layers to a depth of at least 2 feet should be examined. The following current ASTM test designations may be used in developing the necessary data where appropriate for design: Plastic Limit and Plasticity Index . . . . . . . . D4318 Grain Size Analysis . . . . . . . . . . . . . . . . . . . . D421 (Sample Preparation) D422 (Test Procedure) Compaction Test . . . . . . . . . . . . . . . . . . . . . . D698 D1557 Unconfined Compression Test . . . . . . . . . . . D2166 b. Where cohesive soils exist in the subgrade, resulting of an unconfined compression test of the compacted cohesive material (saturated) will give a cohesion or shear strength for use in design. It may not be necessary to develop shear values from tests for some non-cohesive soils but where necessary standard tests may be performed. In absence of testing, caution is advised in applying the AREMA allowable bearing pressure of 20 psi for design from Chapter 16, Economics of Railway Engineering and Operations. c. The level of stress in the subgrade should not exceed an allowable bearing pressure that includes a safety factor. A minimum factor safety of a least 2 and as much as 5 or more should be provided to prevent bearing capacity failure or undue creep under the loaded area. When subgrade support is marginal and/or where the liquid limit of the subgrade soil exceeds a value of 30 or the plasticity index exceeds 12, special attention should be given to that soil. A change of subgrade soil or stabilization of the subgrade material may be considered to obtain a more reliable support for the sub-ballast. 2.11.2.2 Loads Supported by Track Ballast a. Many variables affect the stress placed by the wheel load on the tie and the load is distributed over many ties. b. Example calculation follows: (1) Problem: Develop ballast depth below base of tie for a proposed track supporting a 36 inches diameter wheel (36,000-lb wheel load) at speed of 55 mph, 136-lb rail and 798–6 oak ties @ 21 inches spacing. Assume a saturated subgrade support value of 18 psi includes a safety factor of 2. (2) The AREMA impact factor for track: 33V/100D where: V = velocity in mile per hour D = diameter of the wheel Impact Factor = (33 55) / (100 36) = 1,815/3,600 = 0.50. (3) Distribution Factor: For 21 inches tie spacing 47% of axle load is assumed applicable to each tie either side of the applied load. (Arrived at by using Talbot distribution utilizing a track modulus of 3,500 lb per inch per inch). © 2010, American Railway Engineering and Maintenance-of-Way Association 1-2-20 AREMA Manual for Railway Engineering Ballast (4) AREMA formula for average ballast pressure (psi) at tie face: ABP = [2P (1 + IF/100) (DF/100)]/A where: P= IF = DF = A= 36,000 (Wheel loading in lb) 50 (Impact factor in percent) 47 (Distribution factor in percent) 918 Area of face of 7 9 8 -6ties in sq in. ABP = Average ballast pressure at base of tie ABP = [2 3,600 (1 + 50/100) (47/100)]/918 = 55 psi 2.11.2.3 Depth of Ballast Plus Sub-ballast a. The distribution of loads to depth is approximately the same regardless of the granular material. Therefore the combined depth of sub-ballast and ballast is calculated as a single unit to develop the pressure on the subgrade. Talbot developed an empirical formula for vertical pressure exerted by the ballast under the tie at its intercept with the rail at a depth below the bottom surface of the tie. pc = 16.8 pa/h1.25 1 where: pc = bearing pressure on subgrade including safety factor pa = uniformly distributed pressure over tie face h = depth below face in inches b. If the tie pressure pa in pounds per square inch and the bearing capacity of the subgrade pc are known, the minimum depth of ballast in inches required to produce a stable structure is: 3 h = (16.8 pa/pc)4/5 c. Assuming an allowable subgrade pressure of 18 psi (a safety factor of 2) and using the unit tie face pressure developed above of 55 psi, solve for ballast depth: h = (16.855/18)4/5 = (924.0/18.0)4/5 = 23.4 inches d. The capacity of the subgrade including the safety factor must always be equal to or greater than the load placed upon it. 2.11.2.4 Location of Ballast – Sub-ballast Interface The sub-ballast layer depends upon its state of compaction to be most effective. The present specified depth of 12 inches of track ballast below the tie precludes the maintenance tamping from penetrating and damaging the sub-ballast layer. The force calculated by the above formula for a point 12 inches beneath the tie is 41.4 psi, a force that will reduce tendency of larger ballast particles to penetrate the sub-ballast. The remaining depth of required ballast is furnished by the sub-ballast. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-2-21 4 Roadway and Ballast 2.11.2.5 Sub-ballast Materials a. Material most commonly available for use as sub-ballast are those aggregates ordinarily specified and used in construction for highway bases and subbases. These include crushed stone, natural or crushed gravels, natural or manufactured sands, crushed slag or a homogeneous mixture of these materials. Other natural on site materials conforming to proper engineering standards and specifications as may be defined by individual railway companies may be used. b. The sub-ballast shall be a granular material so graded as to prevent penetration into the subgrade and penetration of track ballast particles into the sub-ballast zone. Applying the filter principle used in drainage to the grading of the subgrade material will determine the grain size distribution of the subballast. Most state highway specifications include standard gradations for dense graded aggregate (DGA) and aggregate base course (ABC). These gradations may meet the requirements for use as sub-ballast. Other standard gradations may also meet these requirements. c. Prepare the gradation curve for the sub-ballast by plotting the grain size distribution for the subgrade on a semi-logarithmic paper, using the logarithmic scale for the grain sizes and the natural scale for percent passing. Determine the grain-sizes at 15%, and 50% points on the chart. Use these values with relevant ratios from Table 1-2-3 to compute the limiting grain sizes at the 15% and 50% passing lines on the chart. The maximum grain size of the sub-ballast must not exceed the maximum grain size of the track ballast. No more than 5% of the sub-ballast should pass the No. 200 sieve. Construct lines connecting the minimum and maximum points to set limits for the sub-ballast material. See example Figure 1-2-5. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-2-22 AREMA Manual for Railway Engineering Ballast Table 1-2-3. Requirements for Filter Material (after USBR1963) Character of Filter Materials Ratio R50 Ratio R15 5 to 10 – 12 to 58 12 to 40 9 to 30 6 to 18 Uniform grain-size distribution (U = 3 to 4) Well graded to poorly graded (non-uniform); subrounded grains Well graded to poorly graded (non-uniform); angular particles R50 = D50 of filter material / D50 of material to be protected Note: R15 = D15 of filter material / D15 of material to be protected Grain-size curves (semilogarithmic plot) of sub-ballast and subgrade should be approximately parallel in the finer range of sizes. This table was prepared especially for earth dam design and since the use here is for a different purpose the values given may be slightly exceeded. In event that soil in subgrade may be subject to piping, position the maximum percentage value of D for the sub-ballast to be less than 5 ¥ D85 of the subgrade soil. The sub-ballast in this case should be well graded. 1 3 4 Figure 1-2-5. Example Using Table 1-2-4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-2-23 Roadway and Ballast 2.11.3 TESTING (1996) Some of the most frequently used tests for sub-ballast material are given in Table 1-2-4 which state properties, test methods, and comments on limiting values. Table 1-2-4. Sub-ballast Properties and Test Methods Property Test Method Comments Particle Size Analysis ASTM D 422 See Article 2.11.2.5 Moisture Density Relation ASTM D 1557 Maximum Dry Density and Optimum Moisture Content Liquid and Plastic Limits Minus No. 40 Sieve ASTM D 423 ASTM D 424 See Design Section Degradation–Los Angeles Abrasion ASTM C 131 Variable (Note 1) Sodium Sulphate Soundness ASTM C 88 Variable (Note 1) Percent Material Passing No. 200 Sieve ASTM C 117 Variable (Note 1) Permeability ASTM D 2434 Variable (Note 1) Specific Gravity ASTM C 127 Variable (Note 1) Note 1: The numerical value of these tests will depend upon the physical and chemical characteristics of both the ballast and subgrade as well as the material used for sub-ballast and values as may be defined by the individual railway companies. 2.11.4 CONSTRUCTION OF SUB-BALLAST SECTION (1996) a. The subgrade shall have been graded, shaped and compacted as required by the plans and specifications. The top of the subgrade requires special attention to obtain uniform density. A uniformly smooth surface compacted to specifications is required, containing no ruts, pot holes, loose soil or any imperfection retaining water on the surface. The surface shall be inspected by the engineer and if surface fails to conform to specifications the engineer may require blading, rolling and compacting to provide a satisfactory surface. b. The sub-ballast material shall be transported and delivered to the site in a manner that will prevent segregation or loss of material. The material shall be placed in layers of 3 inches to 6 inches (or as directed by the engineer) and compacted to depth and density as required by the plans and specifications. The sub-ballast shall be shaped as required by the plans and specifications and the finished surface shall be free from surface defects and imperfections that will retain water or restrict free flow of water. c. Vehicular traffic is to be kept to a minimum across the newly prepared sub-ballast surface. The contractor shall be responsible for maintaining a firm, true and smooth surface compacted to the required density until track ballast is placed on the sub-ballast. 2.11.5 PRODUCTION AND HANDLING Production and handling shall conform to Section 2.5, Production and Handling, of this chapter for track ballast. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-2-24 AREMA Manual for Railway Engineering Ballast 2.11.6 INSPECTION (1996) Inspection of material at production site shall conform to Section 2.7 of this chapter. 2.11.7 MEASUREMENT AND PAYMENT (1996) a. The pay item for furnishing, placing, shaping, compacting and maintaining the sub-ballast until acceptance by the railway shall be “sub-ballast” and the pay unit shall be by the ton. b. Measure and payment for water used to moisten subgrade prior to placing the sub-ballast, in mixing subballast material to maintain proper moisture during compaction and maintenance of the surface during construction shall not be measured for separate payment but shall be considered incidental to subballast payment. COMMENTARY (1988) a. Sub-ballast exists under most of all railroad tracks as a result of degradation of track ballast material. Most of our rail lines are over a century old and during that period weathering and mechanical forces from traffic have reduced the size of the earlier ballasts to much smaller particles. b. Sub-ballast is used in new construction and rehabilitation of the track substructure when the entire track superstructure has been removed to rebuild the subgrade. The sub-ballast performs several important functions: 1 (1) The sub-ballast must be sufficiently impervious to divert most of the water falling into the track to the side ditches to prevent saturation of the subgrade which would weaken the subgrade and contribute to failure under load. (2) The sub-ballast must be sufficiently pervious to permit release of the capillary water or seepage of water to prevent the accumulation of water below the sub-ballast. This condition could cause failure of the subgrade. If the sub-ballast material is not sufficiently pervious, a layer of sand or other suitable material meeting engineering standards as outlined in this specification should be constructed between the subgrade and sub-ballast sections of the roadway structure. (3) The sub-ballast must possess sufficient strength to support the load applied by the ballast section and transfer the load to the subgrade. (4) A sufficient thickness of non-frost susceptible sub-ballast should be provided in those installations where extreme environmental conditions (freezing and thawing) are encountered. (5) The finished surface of the sub-ballast section should be stable to provide a construction platform for placing the track ballast and superstructure without rutting or other surface irregularities which could pocket water. As defined, there are many preferred characteristics which will determine the performance of a suitable sub-ballast material. Therefore, it is imperative for the engineer to follow established engineering principles and select those materials meeting performance criterion commensurate with roadway stability requirements. The Engineer may also define other tests of a proposed sub-ballast material in addition to the tests outlined in Table 1-2-4 to define other properties of the track ballast and subgrade where unusual subgrade or ballast conditions exist. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-2-25 3 4 Roadway and Ballast SUMMARY (1988) a. The AREMA Ballast Specification is intended as a guideline and cannot cover all of the requirements necessary for the full appraisal of the in track performance of a ballast material. It is not possible to incorporate into the laboratory tests those field factors which include geographical and climatic conditions, load variations, subgrade conditions, and other conditions which will actually determine the total in track performance of a ballast material. Generally, the revised specifications have established material standards and test requirements which will provide more efficient ballast materials commensurate with current roadbed structure and performance requirements. b. The AREMA Ballast Committee will continue to pursue the multiple ballast testing programs and will modify the ballast specification, as required, to produce a more definitive ballast specification for the railroad industry. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-2-26 AREMA Manual for Railway Engineering 1 Part 3 Natural Waterways — 2005 — TABLE OF CONTENTS Section/Article Description Page 3.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.1 Scope (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.2 Importance (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-4 1-3-4 1-3-5 3.2 Drainage Basin Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1 General (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-5 1-3-5 3.3 Capacity of Waterway Openings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1 General (1984) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.2 Methods (1984) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.3 Summary (1984) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-7 1-3-7 1-3-8 1-3-18 3.4 Basic Concepts and Definitons of Scour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.1 Scour (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.2 Long-term Elevation Streambed Changes (Aggradation and Degradation) (2005) . . . . . 3.4.3 Contraction Scour (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.4 Local Scour (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.5 Lateral Stream Migration (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.6 Total Scour (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.7 References for Section 3.4 (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-20 1-3-20 1-3-21 1-3-22 1-3-22 1-3-23 1-3-24 1-3-24 3.5 Calculating Scour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.1 Predicting Aggradation and Degradation (2005). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.2 Predicting Lateral Migration (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.3 Estimating Contraction Scour (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.4 Estimating Local Pier Scour (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.5 Evaluating Local Scour at Abutments (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.6 Total Scour Calculation Problem (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.7 References for Section 3.5 (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-25 1-3-25 1-3-28 1-3-31 1-3-43 1-3-49 1-3-53 1-3-59 3.6 Protecting Roadway and Bridges From Scour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.1 Embankment (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.2 Bridges (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.3 Countermeasure Selection (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-60 1-3-60 1-3-61 1-3-62 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-1 1 3 Roadway and Ballast TABLE OF CONTENTS (CONT) Section/Article 3.6.4 Description Page Countermeasure Design Guidance (2005). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-77 3.7 Means of Protecting Roadbed and Bridges from Washouts and Floods . . . . . . . . . . . . 3.7.1 General (1996) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.7.2 Roadway (1996). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.7.3 Bridges (1996) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-145 1-3-145 1-3-145 1-3-146 3.8 Construction and Protection of Roadbed Across Reservoir Areas . . . . . . . . . . . . . . . . 3.8.1 General (1978) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.8.2 Determination of Wave Heights (1978). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.8.3 Construction of Embankment and Roadbed (1978) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.8.4 Construction of Embankment Protection (1978) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-147 1-3-147 1-3-147 1-3-153 1-3-154 3.9 Glossary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-156 LIST OF FIGURES Figure 1-3-1 1-3-2 1-3-3 1-3-4 1-3-5 1-3-6 1-3-7 1-3-8 1-3-9 1-3-10 1-3-11 1-3-12 1-3-13 1-3-14 1-3-15 1-3-16 1-3-17 1-3-18 1-3-19 1-3-20 1-3-21 1-3-22 1-3-23 1-3-24 1-3-25 1-3-26 1-3-27 1-3-28 1-3-29 1-3-30 Description Page Log Pearson Type III Exceedance Probability Plot. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Velocities of Flow, Rural Watersheds (Reference 49) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Curve Number Method for Estimating Lag (L) [L = 0.6tc], Urban Watersheds (Reference 49) Pier Scour Depth in a Sand-bed Stream as a Function of Time. . . . . . . . . . . . . . . . . . . . . . . . . Schematic Representation of Scour at a Cylindrical Pier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Specific Gage Data for Cache Creek, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flow Patterns in Meanders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case 1A: Abutments Project into Channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case 1B: Abutments at Edge of Channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case 1C: Abutments Set Back from Channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case 2A: River Narrows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case 2B: Bridge Abutments and/or Piers Constrict Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case 3: Relief Bridge Over Floodplain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case 4: Relief Bridge Over Secondary Stream. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fall Velocity of Sand-sized Particles with Specific Gravity of 2.65 in Metric Units . . . . . . . . . Comparison of Scour Equations for Variable Depth Ratios (y/a) (HEC-18) . . . . . . . . . . . . . . . Common Pier Shapes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multiple Columns Skewed to the Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Topwidth of Scour Hole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Schematic Representation of Abutment Scour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scour of Bridge Abutment and Approach Embankment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Orientation of Embankment Angle, q, to the Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Abutment Shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross Section for Total Scour Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hydraulic Data for Contraction Scour Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hydraulic Data for Local Scour Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Total Scour Plot. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Comparison of Channel Bend Cross Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Effect of Turbulence Intensity on Rock Size Using the Isbash Approach . . . . . . . . . . . . . . . . . Placement of Pier Riprap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-9 1-3-18 1-3-19 1-3-21 1-3-23 1-3-26 1-3-29 1-3-34 1-3-35 1-3-36 1-3-37 1-3-38 1-3-39 1-3-39 1-3-41 1-3-44 1-3-45 1-3-47 1-3-49 1-3-50 1-3-50 1-3-52 1-3-52 1-3-54 1-3-55 1-3-57 1-3-59 1-3-72 1-3-79 1-3-80 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-2 AREMA Manual for Railway Engineering Natural Waterways LIST OF FIGURES (CONT) Figure 1-3-31 1-3-32 1-3-33 1-3-34 1-3-35 1-3-36 1-3-37 1-3-38 1-3-39 1-3-40 1-3-41 1-3-42 1-3-43 1-3-44 1-3-45 1-3-46 1-3-47 1-3-48 1-3-49 1-3-50 1-3-51 1-3-52 1-3-53 1-3-54 1-3-55 1-3-56 1-3-57 1-3-58 1-3-59 1-3-60 1-3-61 1-3-62 1-3-63 1-3-64 1-3-65 1-3-66 1-3-67 1-3-68 1-3-69 1-3-70 1-3-71 1-3-72 1-3-73 1-3-74 1-3-75 Description Page Section View of a Typical Setup of Spill-through Abutment on a Floodplain With Adjacent Main Channel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-81 Plan View of the Location of Initial Failure Zone of Rock Riprap for Spill-through Abutment 1-3-82 Characteristic Average Velocity for SBR<5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-84 Characteristic Average Velocity for SBR>5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-85 Characteristic Average Velocity for SBR>5 and SBR<5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-86 Plan View of the Extension of Rock Riprap Apron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-87 Typical Guide Bank (Modified from Bradley). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-89 English Version of Nomograph to Determine Guidebank Length (after Bradley) . . . . . . . . . . 1-3-91 Example Guide Bank Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-94 Extent of Protection Required at a Channel Bend (after USACE) . . . . . . . . . . . . . . . . . . . . . . . 1-3-97 Definition Sketch for Spur Angle (after Karaki 1959) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-98 Launching of Stone Protection on a Riprap Spur . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-100 Gabion Spur Illustrating Flexible Mat Tip Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-101 Permeable Wood-slat Fence Spur Showing Launching of Stone Toe Material (after Brown) . 1-3-102 Relationship Between Spur Length and Expansion Angle for Several Spur Permeabilities (after Brown). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-103 Spur Spacing in a Meander Bend (after Brown) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-103 Typical Straight, Round Nose Spur . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-105 Impermeable Spur Field in Top Photograph With Close-up Shot of One Spur in the Lower Photograph, Vicinity of the Richardson Highway, Delta River, Alaska . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-106 Example of Spur Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-107 Angle of Repose of Riprap in Terms of Mean Size and Shape of Stone (Chen and Cotton 1988) 1-3-110 Methods of Providing Toe Protection (USACE 1991) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-114 Alternative Method of Providing Toe Protection (HEC-11) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-115 Flank Details (HEC-11) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-116 Rock-fill Trench (after HDS 6) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-118 Windrow Revetment, Definition Sketch (after USACE 1981). . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-119 Typical Sand-cement Bag Revetment (after Brown 1985). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-121 Typical Stacked Block Gabion Revetment Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-124 Gabion Basket Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-126 Schematic of a Vertical Drop Caused by a Check Dam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-128 Design Example of Scour Downstream of a Drop Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-130 Encroachment on a Meandering River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-132 Perspective View of Hardpoint Installation With Section Detail (after Brown) . . . . . . . . . . . . 1-3-137 Typical Jack Unit (after Brown) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-138 Retarder Field Schematic (after HDS 6). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-138 Timber Pile Bent Retarder Structure (after Brown) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-139 Typical Wood Fence Retarder Structure (after Brown). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-140 Light Double Row Wire Fence Retarder Structure (after Brown) . . . . . . . . . . . . . . . . . . . . . . . 1-3-140 Heavy Timber-pile and Wire Fence Retarder Structure (after Brown) . . . . . . . . . . . . . . . . . . . 1-3-141 Typical Longitudinal Rock Toe-dike Geometries (after Brown) . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-143 Longitudinal Rock Toe-dike Tiebacks (after Brown) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-143 Timber Pile, Wire Mesh Crib Dike With Tiebacks (after Brown) . . . . . . . . . . . . . . . . . . . . . . . . 1-3-144 Anchorage Schemes for a Sheetpile Bulkhead (after Brown) . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-144 Wave Heights and Minimum Wind Durations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-149 Wave Periods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-150 Fetch Example Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-151 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-3 1 3 4 Roadway and Ballast LIST OF FIGURES (CONT) Figure Description Page 1-3-76 Wave Run-up Ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-152 LIST OF TABLES Table 1-3-1 1-3-2 1-3-3 1-3-4 1-3-5 1-3-6 1-3-7 1-3-8 1-3-9 1-3-10 1-3-11 1-3-12 1-3-13 1-3-14 1-3-15 1-3-16 1-3-17 1-3-18 1-3-19 1-3-20 1-3-21 1-3-22 1-3-23 Description Page Rural Area Runoff Coefficient Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Urban Area Runoff Coefficient Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Storm Duration Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Values of N in the Kerby Formula . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Values of c in Izzard Formula. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Soil Type Groupings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Determining Antecedent Moisture Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Curve Numbers for Various Cover and Soil Types [AMC = II] (Reference 50) . . . . . . . . . . . . Antecedent Moisture Condition to Curve Number Conversion . . . . . . . . . . . . . . . . . . . . . . . . . Correction Factor, K1, for Pier Nose Shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Correction Factor, K2, for Angle of Attack, q, of the Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Increase in Equilibrium Pier Scour Depths, K3, for Bed Condition . . . . . . . . . . . . . . . . . . . . . Abutment Shape Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stream Instability and Bridge Scour Countermeasures Matrix . . . . . . . . . . . . . . . . . . . . . . . . . Coordinates for Guide Bank on the Right Bank of Figure 10.4 . . . . . . . . . . . . . . . . . . . . . . . . . Rock Riprap Gradation Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Riprap Gradation Classes (English) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Standard Gabion Sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . River Response to Cutoffs (HDS 6) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wind Relationship – Land to Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wave Height Distributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sample Computation for Determining Wave Height and Protection Needs . . . . . . . . . . . . . . . Filter Blanket Limits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-10 1-3-11 1-3-12 1-3-12 1-3-12 1-3-14 1-3-14 1-3-15 1-3-16 1-3-45 1-3-46 1-3-46 1-3-52 1-3-64 1-3-96 1-3-112 1-3-112 1-3-124 1-3-135 1-3-148 1-3-149 1-3-153 1-3-155 SECTION 3.1 GENERAL1 3.1.1 SCOPE (1992) This subject concerns the determination of the location, size, and shape of drainage structures. It also includes consideration of flood flows and water-borne materials in surface waters, the protection of the roadway in contact with surface water, and the protection of structures carrying tracks over waterway openings. 1 References, Vol. 39, 1938, pp. 322, 786; Vol. 51, 1950, pp. 706, 839; Vol. 54, 1953, pp. 1087, 1385; Vol. 62, 1961, pp. 678, 936; Vol. 73, 1972, p. 143; Vol. 85, 1984, p. 5; Vol. 93, 1992, p 34. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-4 AREMA Manual for Railway Engineering Natural Waterways 3.1.2 IMPORTANCE (1992) Properly designed openings, control of flood flows, and protection of roadway and structures are of vast importance from the standpoints of safety, economy, and continuity of operation during flood periods. With the ever-present menace of floods and then disastrous consequences, every related problem is deserving of accurate and exhaustive survey and careful planning. SECTION 3.2 DRAINAGE BASIN DATA1 3.2.1 GENERAL (1992) a. Survey requirements depend in some degree upon whether the waterways are to be crossed by a new line, or whether the replacement of an existing waterway structure is involved. b. For the crossing of a new line the survey requirements are extensive and general in nature, involving the determination of the drainage area and its shape; the stream and slope profile; soil, vegetation and climatic characteristics; as well as topographical details in the vicinity of the most probable point of crossing. c. For the replacement of an existing waterway structure the survey requirements may be the same as those for a new line, but in many cases the required waterway area will likely be determined from past performance of the stream at the structure to be replaced. Observation may have indicated that a change in size, shape or location of the waterway structure may be desirable. Maintenance of railroad operation during construction and how well the existing structure fits into the local topography may control the design of the new structure. All such facts should be considered in determining survey requirements. d. Consideration should always be given to probable future changes in conditions above and below the point of crossing which would in any way affect the performance of the stream – for example, channel improvements and the construction or removal of dams or revetments. Also, a search should be made for future subdivision or commercial development plans. e. For small culverts or replacements some of the data listed here may be unnecessary and some will have been predetermined, but all of the following items should be considered in order that survey notes may include all the information necessary for the design of the most suitable structure: (1) Area of drainage basin. (2) Shape and contour of drainage basin. (3) Location, length and slope of defined channels. (4) Slope of stream bed and side slopes. (5) Character of soil and subsoil. (6) Vegetation – timber, grass, cultivated or barren, and probable changes. 1 References, Vol. 39, 1938, pp. 322, 786; Vol. 51, 1950, pp. 706, 839; Vol. 54, 1953, pp. 1087, 1385; Vol. 62, 1961, pp. 678, 936; Vol. 73, 1972, p. 143; Vol. 85, 1984, p. 5; Vol. 93, 1992, p 34. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-5 1 3 4 Roadway and Ballast (7) Climatic conditions – accumulation of snow and ice. (8) Precipitation – local records, if any, of intensity, duration, frequency, and temporal and area distribution. (9) Natural and artificial storage – lakes, swamps, reservoirs. (10) Channel course – fixed or changeable. (11) Channel material – rock, boulders, gravel, sand, clay, silt. (12) Channel erosion – amount and nature of material transported. (13) Possibility of ice gorges, or drift accumulations. (14) Elevation of backwater from larger stream below crossing. (15) Determination of past flood crests and frequency. On an existing line crossing a wide valley with two or more openings secure high water profile across the valley on both sides of the railroad embankment. (16) Character of current – rate of flow – steady or variable. (17) Waterway area, relative flood flows and adequacy of existing drainage structures nearby on the waterway. (18) Topography over liberal area in vicinity of crossing. Typical flood channel sections. (19) Location of right-of-way limits. (20) Property lines and owners names along stream if channel change is contemplated. (21) Track profile, alignment and topography for sufficient distance to cover any probable change, or as necessary to portray conditions. (22) Borings locate and give character of material found. (23) Determine most favorable angle of stream crossing. (24) Location – mile post and survey station. (25) Location of borrow pit if bridge filling is involved. (26) Location and elevation of improvements which might be subject to flooding by backwater upstream from track. (27) Flood plain regulations and studies, if available. (28) Governmental regulations and requirements. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-6 AREMA Manual for Railway Engineering Natural Waterways SECTION 3.3 CAPACITY OF WATERWAY OPENINGS1 3.3.1 GENERAL (1984) a. In the past, in the design of drainage structures, it was considered sufficient to provide a waterway opening of a certain area, based on an area formula (e.g. Talbot’s formula); also, in case the flow (Q) were known, one could assume a velocity of flow (V) (usually taken as 10 feet per sec) and, thus, arrive at the required area (A) of opening. Modern practice is to first calculate the drainage, or flow, then to design the structure to accommodate the flow (Reference 6) using the principles of hydraulics. b. Before deciding on the hydraulic capacity to be provided in a structure, it is advisable to make a thorough search to determine what precipitation and stream flow records are available in the general region of the project site. Where data and time are available, several methods of determining the required capacity should be used, and their results compared before a decision is made. Extensive study and research are in continuous progress by various public agencies in the field of flood runoff and waterway requirements, and it is expected that much additional useful data will be developed. c. These agencies are much better suited, both in full-time personnel in this specialized field and in access to pertinent data as quickly as it becomes available, than are most railroads. Therefore, the needs of railroad personnel dealing with drainage matters are best served by having at hand a list of agencies through which they can obtain the latest information on the subject. In order to take full advantage of this and to insure uniformity of design criteria on the individual railroad, it is advisable that all drainage recommendations and supporting data should clear through a designated “drainage engineer” before final decision. 1 d. A list of Federal and State agencies in the United States that are engaged in research, accumulation of data, and the statistical analysis of precipitation and runoff is given below: • Federal United States Geological Survey Water Supply Papers Flood Magnitude-Frequency Reports Federal Highway Administration Transportation Research Board Soil Conservation Service Corps of Engineers, U.S. Army Water and Power Resources Service National Oceanic and Atmospheric Administration 3 4 • State Highway Departments Water Resources Department Public Works Departments Universities • County or Parish Highway Departments Public Works Departments In Canada, stream flow data can be secured from the Water Survey of Canada Division of Environment Canada at Ottawa. Stream flow data are, generally, not available for Mexico. 1 References, Vol. 42, 1941, pp. 543, 831; Vol. 53, 1952, pp. 699, 1106; Vol. 54, 1953, pp. 1087, 1385; Vol. 62, 1961, pp. 678, 936; Vol. 73, 1972, p. 144; Vol. 85, 1984, p. 5. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-7 Roadway and Ballast 3.3.2 METHODS (1984) 3.3.2.1 General The recommended methods will be those most easily applied that give the best results with a minimum of available information. The basic data required are covered in Section 3.2, Drainage Basin Data. In addition, an indispensable aid is a collection of topographic maps as published by the U.S. Geological Survey in conjunction with TVA, Mississippi River Commission, U.S. Corps of Engineers, etc. With these data in hand, the engineer can proceed to specific methods. These methods are presented in the sections which follow. 3.3.2.2 Statistical Methods a. When there exist sufficient flow data for the waterway under consideration, a statistical analysis can be undertaken to estimate the probability that a given magnitude of flow can occur or be exceeded (Reference 13). Federal regulations mandate the use of the Log Pearson Type III distribution, a procedure for analyzing extreme events such as maximum yearly discharges for a stream. b. Special plotting paper (probability 2 log cycles) can be used for this analysis by following the steps listed below: (1) Collect runoff data from a stream gaging station near to the desired location, as obtained from such as the U.S. Geological Survey Water Supply Papers. A usable record must have a continuity of data of 20 years or more. (2) Arrange the data by listing in descending order the magnitudes of the largest recorded peak discharges, i.e. the largest first. The ranking is only by discharge quantity and is independent of when the discharge occurred in the period of record. The series may be terminated when the number of peak discharges equals the number of years of record. The peak discharges should then be numbered (labelled) from one to the number of years of record. (3) Calculate the exceedance probability by first calculating the estimated return period for each peak discharge by n + 1 T r = ----------------m EQ 1 where: n = number of years of record m = rank or order number of that particular peak discharge The exceedance probability 1 and represents the probability that the specific peak discharge will occur or beexceeded p = ----Tr (4) Utilizing the plotting paper, select a suitable vertical scale so all the discharge data can be graphed and still allow predicted values to be read. Plot the data of peak discharges on the vertical axis and the exceedance probability (%) on the horizontal axis. Fit the best straight line to the plotted data. As an example, using Figure 1-3-1, the probability that a discharge of 10,000 c.f.s. will be equalled or exceeded is 10.9% (i.e. a return period of 9.1 years) for this record. Again, using Figure 1-3-1, the 100-year discharge (100 year return period or 1% exceedance probability) is 15,800 c.f.s. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-8 AREMA Manual for Railway Engineering Natural Waterways c. The design flood frequency to be used is a matter of engineering judgment and economics. A number of trials should be made using a wide range of frequencies. In this way the possibilities of damage because of too small an opening can be assessed. The cost of providing for the maximum possible flood of 100 year frequency or greater can also be determined and a prudent decision made. In general practice, railroad drainage openings should be designed for floods in the range of 25 to 50 years. This does not imply that a 100-year flood design would be out of place in certain instances. Because of the susceptibility of railroads to legal action for damages, it would probably be unwise to design for less than a 25-year flood, except in special instances where results of lesser design are fully understood. d. After the design flow in cubic feet per second has been determined, the basic hydraulic formula Q = AV can be used to determine the average velocity in feet per second through a given area of opening in square feet. For structures on unstable soils, 3 feet per sec may be the maximum allowable velocity without damaging scour; generally, 3 to 6 feet per sec will cause little, if any, scour in fairly good soils. Culverts and other paved waterways are frequently designed for flows as high as 10 feet per sec. If time permits and greater refinement is desired, there is a multitude of hydraulics texts and manuals available for the design of waterway openings, (Reference 6 and 45). 1 3 4 Figure 1-3-1. Log Pearson Type III Exceedance Probability Plot © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-9 Roadway and Ballast 3.3.2.3 The Rational Method 3.3.2.3.1 General a. The rational method is an old, simple, widely used (and often criticized) method employed in the determination of peak discharges from a given watershed. The method is based on the idea that the peak rate of surface outflow from a given watershed will be proportional to the watershed area and the average rainfall intensity over a period of time just sufficient for all parts of the watershed to contribute to the outflow (Reference 38). The constant of proportionality is then supposed to reflect all those characteristics of the watershed. In its simplest form, the rational formula is written as EQ 2 Q = CiA where: Q = peak discharge (cubic feet per second – cfs) C = ratio or peak runoff rate to average rainfall rate over the time of concentration (runoff coefficient) i = rainfall intensity (inches/hour) A = area of watershed under consideration (acres) b. In general the rational method should be applied to drainage basins less than 200 acres in area and is best suited for well-defined drainage basins, such as urban areas. 3.3.2.3.2 Determining Runoff Coefficient a. Values of runoff coefficient are given separately for rural areas and urban areas in Table 1-3-1 and Table 1-3-2, as taken from Schwab, et al (Reference 46). Table 1-3-1. Rural Area Runoff Coefficient Values Vegetation and Topography Soil Texture Open Sandy Loam Clay and Silt Loam Tight Clay Woodland Flat 0-5% slope 0.10 0.30 0.40 Rolling 5-10% slope 0.25 0.35 0.50 Hilly 10-30% slope 0.30 0.50 0.60 Pasture Flat 0.10 0.30 0.40 Rolling 0.16 0.36 0.55 Hilly 0.22 0.42 0.60 Cultivated Flat 0.30 0.50 0.60 Rolling 0.40 0.60 0.70 Hilly 0.52 0.72 0.82 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-10 AREMA Manual for Railway Engineering Natural Waterways Table 1-3-2. Urban Area Runoff Coefficient Values Description of Area Runoff Coefficients Business Downtown Neighborhood 0.70 to 0.95 0.50 to 0.70 Residential Single-family Multi-units, detached Multi-units, attached Residential (suburban) Apartment 0.30 to 0.50 0.40 to 0.60 0.60 to 0.75 0.25 to 0.40 0.50 to 0.70 Industrial Light Heavy 0.50 to 0.80 0.60 to 0.90 Miscellaneous Parks, cemeteries Playgrounds Railroad yard Unimproved 0. 10 to 0.25 0.20 to 0.35 0.20 to 0.35 0.10 to 0.30 1 b. The runoff coefficient is influenced by many variables, and does not remain constant during a given storm. Thus, “engineering judgment” must be liberally applied in the selection of the coefficient magnitude. 3 3.3.2.3.3 Determining Rainfall Intensity a. The rainfall intensity is the average value in inches per hour during the time of concentration which, by definition, is the time required for runoff to flow from the most remote part of the drainage area to the outlet structure. 4 b. Rainfall intensity relations will usually fit the following equation: m cT i = -------------------n t + d EQ 3 where: i = intensity (inches/hour) T = return period (years) t = storm duration (minutes) c, d, m, n = regional coefficients c. As an example, Fair et al (Reference 22) found that in Indiana the following magnitudes apply: 5 < c < 50 0 < d < 30 0.1< m < 0.5 0.4 < n < 1.0 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-11 Roadway and Ballast d. Reference may also be made to the rainfall intensity curves presented by various publications (Reference 24 and 26). These data may be used in the rational formula in concert with the appropriate storm duration. e. The appropriate return period has been discussed in Article 3.3.2.2 and the reader is referred to that discussion. f. The appropriate storm duration may be calculated from the information found in Table 1-3-3. Table 1-3-3. Storm Duration Calculations Name Ragan (1972) (Reference 45) Kerby (1959) (Reference 34) Izzard (1946) (Reference 32) Equation for t Notes n varies from about 0.025 to 0.040 for flow over natural earthen materials EQ 4 0.6 0.6 L n t = --------------------0.4 0.3 i s NL 0.467 t = 0.827 --------- 0.5 s –2 3 2 0.0007i + c iL t = ------ -----------------------------L ----------------13 60 43200 S L < 1200 ft; N as in Table 1-3-4 EQ 5 for iL < 500; c as in Table 1-3-5 EQ 6 t = overland flow time (min), considered to be equal to storm duration L = basin length (ft) S = basin slope (ft/ft) i = rainfall intensity (in/hr) Table 1-3-4. Values of N in the Kerby Formula Type of Surface N Smooth impervious surface 0.02 Smooth bare packed soil 0.10 Poor grass, cultivated row crops or moderately rough bare surface 0.20 Deciduous timberland 0.60 Pasture or average grass 0.40 Conifer timberland, deciduous timberland with deep forest litter or dense grass 0.80 Table 1-3-5. Values of c in Izzard Formula Surface N Smooth asphalt surface 0.007 Concrete pavement 0.012 Tar and gravel pavement 0.017 Closely clipped sod 0.046 Dense bluegrass turf 0.060 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-12 AREMA Manual for Railway Engineering Natural Waterways 3.3.2.3.4 Application of the Rational Method a. Determine the basin area A (acres) by using USGS topographical maps, maps developed from a survey of the area, or plans made specifically for the basin. This area can then be found by use of a planimeter, counting squares, etc. b. By the use of Tables for rural and urban areas from Article 3.3.2.3.2, find the appropriate value of C (runoff coefficient). If the land is a conglomerate of uses, a composite C value may be determined by: C 1 A 1 + C 2 A 2 + YC n A n C comp = -----------------------------------------------------------------At EQ 7 where: C1, C2…Cn are the runoff coefficients associated with component areas A1, A2 …An and At = A1 + A2 + …An. c. Determine the magnitude of rainfall intensity. The storm duration for the basin can be determined by using one of the equations listed in the Table 1-3-3 in Article 3.3.2.3.3. This magnitude is found by knowing the basin length, slope, and cover. d. Determine rainfall intensity by using EQ 3 with appropriate coefficients, or by entering an intensityduration-frequency diagram (Reference 24 and 26). e. The data of paragraph a, paragraph b and paragraph d are then inserted into EQ 1 to yield the predicted peak discharge. 1 3.3.2.4 Soil Conservation Service Curve Number Method 3.3.2.4.1 The Theory a. This method develops the quantity of runoff from a given amount of precipitation, and considers the effects of basin soil and cover types, rainfall depth, and antecedent moisture conditions (Reference 49). b. The total runoff is calculated as the difference between total rainfall and total abstraction, which is the sum of total infiltration and how much water is used to initially wet the surface and fill surface depressions. The method assumes that the ratio of runoff to available water is the same as the ratio of infiltration to ultimate total abstraction. The resulting equation is: 2 P t – 0.2S R t = ------------------------------------ P t + 0.8S EQ 8 where: R(t) = runoff (cumulative) (inches) P(t) = total rainfall (inches) S = ultimate total abstraction c. This calculation is made for 4 or 5 storms of different convenient storm durations to assess which produces the most severe condition. Often local custom dictates which storms must be examined. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-13 3 4 Roadway and Ballast 3.3.2.4.2 Determining the Parameter S a. Soil type is variable, and four groupings have been created based on infiltration capacity. Table 1-3-6 lists these soil criteria: b. Also to be considered is the antecedent moisture condition (AMC), which is an indication of how much rain has fallen on the basin recently. See Table 1-3-7. c. Then, knowing the soil group and the antecedent moisture condition class, a curve number (CN) is established from Table 1-3-8 which is representative of a large variety of conditions. Table 1-3-6. Soil Type Groupings Soil Group Characteristics A Soils in this category have a high infiltration rate even when thoroughly wetted and consist mainly of deep, well-to excessively-drained sands or gravels. (Low runoff potential) B Soils in this category have moderate infiltration rates when thoroughly wetted and consist of moderately deep to deep, moderately well to well-drained soils with moderately fine to moderately coarse textures. C Soils in this category have slow infiltration rates when thoroughly wetted and consist mainly of soils with a layer that impedes downward movement of water, or soils with moderately fine to fine textures. D Soils in this category have a very slow infiltration rate when thoroughly wetted and consist mainly of clay soils with high swelling potential, soils with a permanently high water table, soils with a claypan or clay layer at or near the surface, and shallow soils over nearly impervious material. (High runoff potential) Table 1-3-7. Determining Antecedent Moisture Condition Antecedent Moisture Condition Class 5-Day Antecedent Rainfall (inches) Dormant Season Growing Season I Less than 0.5 Less than 1.4 II 0.5 1.1 1.4 2.1 III over 1.1 over 2.1 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-14 AREMA Manual for Railway Engineering Natural Waterways Table 1-3-8. Curve Numbers for Various Cover and Soil Types [AMC = II] (Reference 50) Land Use Description Hydrologic Soil Group A B C D 72 62 81 71 88 78 91 81 Pasture or range land: poor condition good condition 68 39 79 61 86 74 89 80 Meadow: good condition 30 58 71 78 Wood or forest land: 45 25 66 55 77 70 83 77 Open spaces: lawns, parks, golf course, cemeteries, etc., good condition: grass cover on 75% or more of the area fair condition: grass cover on 50% to 75% of the area 39 49 61 69 74 79 80 84 Commercial and business areas (85% impervious) 89 92 94 95 Industrial districts (72% impervious) 81 88 91 93 77 61 57 54 51 85 75 72 70 68 90 83 81 80 79 92 87 86 85 84 Paved parking lots, roofs, driveways, etc. (Note 3) 98 98 98 98 Streets and roads: paved with curbs and storm sewers (Note 3) gravel dirt 98 76 72 98 85 82 98 89 87 98 91 89 69-71 71-73 73-75 75-78 77-80 79-82 82-84 84-86 86-88 86 88 90 Cultivated Land: without conservation treatment with conservation treatment thin stand, poor cover, no mulch good cover Residential (Notes 1 and 4): Average Lot Size 1/8 acre or less 1/4 acre 1/3 acre 1/2 acre 1 acre Average % Impervious (Note 2) 65 38 30 25 20 Urban areas: Low density (15-18% impervious surfaces) Medium density (21-27% impervious surfaces) High density (50-75% impervious surfaces) Note 1: Curve numbers are computed assuming the runoff from the house and driveway is directed towards the street with a minimum of roof water directed to lawns where additional infiltration could occur. Note 2: The remaining pervious areas (lawn) are considered to be in good pasture condition for these curve numbers. Note 3: In some warmer climates of the country a curve number of 95 may be used. Note 4: Curve numbers may vary with different parts of the country. The local SCD office should be contacted for recommended numbers in that locality. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-15 1 3 4 Roadway and Ballast d. Knowing the curve number (CN), the value of S (ultimate total abstraction) is found from: 1000 S = ------------- – 10 CN e. EQ 9 If different antecedent moisture conditions exist than those of Group II, the conversions to CN found in Table 1-3-9 may be used (Reference 49): Table 1-3-9. Antecedent Moisture Condition to Curve Number Conversion CN for Condition II 100 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 84 83 82 81 80 79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64 63 62 CN for Condition I 100 97 94 71 89 87 85 83 81 80 78 76 75 73 72 70 68 67 66 64 63 62 60 59 58 57 55 54 53 52 51 50 48 47 46 45 44 43 42 CN for Condition III 100 100 99 99 99 98 98 98 97 97 96 96 95 95 94 94 93 93 92 92 91 91 90 89 89 88 88 87 86 86 85 84 84 83 82 82 81 80 79 CN for Condition II 61 60 59 58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 CN for Condition I 41 40 39 38 37 36 35 34 33 32 31 31 30 29 28 27 26 25 25 24 23 22 21 21 20 19 18 18 17 16 16 15 25 20 15 10 5 0 12 9 6 4 2 0 CN for Condition III 78 78 77 76 75 75 74 73 72 71 70 70 69 68 67 66 65 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 43 37 30 22 13 0 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-16 AREMA Manual for Railway Engineering Natural Waterways 3.3.2.4.3 Application of the CN Method – Total Flow a. Let us assume the CN has been established, and S has been calculated. By selecting a rainfall depth for a particular storm, the runoff may be calculated using EQ 8. The runoff (inches) is multiplied by the basin area, and the result is converted to units of volume of runoff for the basin. b. For a basin which has a conglomerate of soil types, a weighted CN may be calculated from: CN 1 A 1 + CN 2 A 2 + YCN n A n CN comp = ---------------------------------------------------------------------------------At EQ 10 where: CN1, CN2…CNn are the curve numbers associated with component areas A1, A2 … An and At = A1 + A2 … + An. c. The application yields the total amount of runoff from the given rainfall. For design, then, this is repeated for storms of different duration and amount of rainfall. 3.3.2.4.4 Determining Peak Flow from a Rainfall Event a. The peak flow to be expected from a storm many times is more important than the total flow because the peak flow must be carried by the waterway opening. The following procedure is adapted from the principles of the unit hydrograph (Reference 49) and is intended for the designer’s use as a prediction tool. 1 b. The steps in the procedure follow. (1) For the basin, determine: 3 (a) the basin area (square miles) (b) the basin curve number for the soil type(s) and antecedent moisture condition (as in Article 3.3.2.4.2) (c) the depth, and time distribution of the rainfall for the storm in question. 4 (2) Find the time of concentration, tc. This value may be obtained using Figure 1-3-2 for rural watersheds or Figure 1-3-3 for urbanized watersheds. In using Figure 1-3-2, the ordinate is entered with the travel path slope, then the diagonal line which represents the basin characteristics is intercepted, and a velocity is found by reading the abscissa. The time is then found by dividing the travel path by the velocity and appropriate conversions. Figure 1-3-3 utilized the curve number, travel length, and watershed in the calculation of the watershed lag L. This lag is converted to tc by the empirical relationship L = 0.6tc. (3) Calculate peak flow: AR q p = 484 --------------------0.667t c © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-17 Roadway and Ballast where: qp = peak flow (c.f.s.) A = basin area (sq miles) R = runoff depth (inches) (as calculated by EQ 8) tc = time of concentration (hours) c. Repeat paragraph b(1) through paragraph b(3) for storms of different duration and amount of rainfall; for example, durations of from 0.2 to 24 hours, or as load experience dictates, using associated rainfalls from hydrologic records for the locality. More detailed information can be found in Reference 49, as obtained from U.S. Supt. of Documents. 3.3.3 SUMMARY (1984) The procedures of Article 3.3.2 will provide the design engineer with a good estimate of the capacity required for his waterway opening provided the results are used with engineering judgement. For those interested in additional tops in hydrology for engineering use, Reference 8, 17, and 35 are highly recommended. Figure 1-3-2. Velocities of Flow, Rural Watersheds (Reference 49) © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-18 AREMA Manual for Railway Engineering Natural Waterways 1 3 4 Figure 1-3-3. Curve Number Method for Estimating Lag (L) [L = 0.6tc], Urban Watersheds (Reference 49) © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-19 Roadway and Ballast SECTION 3.4 BASIC CONCEPTS AND DEFINITONS OF SCOUR1 3.4.1 SCOUR (2005) 3.4.1.1 Definition Scour is the result of the erosive action of flowing water, excavating and carrying away material from the bed and banks of streams and from around the piers and abutments of bridges. Different materials scour at different rates. Loose granular soils are rapidly eroded by flowing water, while cohesive or cemented soils are more scour-resistant. However, ultimate scour in cohesive or cemented soils can be as deep as scour in sandbed streams. Under constant flow conditions, scour will reach maximum depth in sand-bed and gravel-bed material in hours; cohesive bed material in days; glacial till, sandstones, and shale in months; limestone in years, and dense granite in centuries. Under flow conditions typical of actual bridge crossings, several floods may be needed to attain maximum scour. Determining the magnitude of scour is complicated by the cyclic nature of the scour process. Scour can be deepest near the peak of a flood, but hardly visible as floodwaters recede and scour holes refill with sediment. 3.4.1.2 Clear-Water and Live-Bed Scour There are two conditions for scour at a bridge: clear-water and live-bed scour. Clear-water scour occurs when there is no movement of the bed material in the flow upstream of the crossing or the bed material being transported in the upstream reach is transported in suspension through the scour hole at the pier or abutment at less than the capacity of the flow. At the pier or abutment the acceleration of the flow and vortices created by these obstructions cause the bed material around them to move. Live-bed scour occurs when there is transport of bed material from the upstream reach into the crossing. Live-bed local scour is cyclic in nature; that is, the scour hole that develops during the rising stage of a flood refills during the falling stage. Typical clear-water scour situations include (1) coarse-bed material streams, (2) flat gradient streams during low flow, (3) local deposits of larger bed materials that are larger than the biggest fraction being transported by the flow (rock riprap is a special case of this situation), (4) armored streambeds where the only locations that tractive forces are adequate to penetrate the armor layer are at piers and/or abutments, and (5) vegetated channels or overbank areas. During a flood event, bridges over streams with coarse-bed material are often subjected to clear-water scour at low discharges, live-bed scour at the higher discharges and then clear-water scour at the lower discharges on the falling stages. Clear-water scour reaches its maximum over a longer period of time than live-bed scour (Figure 1-3-4). This is because clear-water scour occurs mainly in coarse-bed material streams. In fact, clearwater scour may not reach a maximum until after several floods. Maximum clear-water pier scour is about 10 percent greater than the equilibrium local live-bed pier scour. 1 Sections 3.4 through 3.6 contain condensed material from Federal Highway Association (FHWA), U.S. Army Corps of Engineers (USACE) and American Society of Civil Engineers (ASCE) publications; primarily FHWA HEC-11, HEC-14, HEC-18, HEC-20, HEC-23, HDS-2 and HDS-6. For more detailed analysis and design information, refer to these organizations and publications. The bibliography at the end of each subsection contains additional references. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-20 AREMA Manual for Railway Engineering Natural Waterways Figure 1-3-4. Pier Scour Depth in a Sand-bed Stream as a Function of Time Live-bed pier scour in sand-bed streams with a dune bed configuration fluctuates about the equilibrium scour depth (Figure 1-3-4). This is due to the variability of the bed material sediment transport in the approach flow when the bed configuration of the stream is dunes. However, with the exception of crossings over large rivers (i.e., the Mississippi, Columbia, etc.), the bed configuration in sand-bed streams will plane out during flood flows due to the increase in velocity and shear stress. For general practice, the maximum depth of pier scour is approximately 10 percent greater than equilibrium scour. For a discussion of bedforms in alluvial channel flow, see Chapter 3 of HDS 6. 1 3 3.4.2 LONG-TERM ELEVATION STREAMBED CHANGES (AGGRADATION AND DEGRADATION) (2005) Aggradation and degradation are long-term streambed elevation changes due to natural or man-induced causes which can affect the reach of the river on which the bridge is located. Aggradation involves the deposition of material eroded from the channel or watershed upstream of the bridge; whereas, degradation involves the lowering or scouring of the streambed due to a deficit in sediment supply from upstream. Long-term bed elevation changes may be the natural trend of the stream or the result of some modification to the stream or watershed. The streambed may be aggrading, degrading, or in relative equilibrium in the vicinity of the bridge crossing. Long-term aggradation and degradation do not include the cutting and filling of the streambed in the vicinity of the bridge that might occur during a runoff event (contraction and local scour). A long-term trend may change during the life of the bridge. These long-term changes are the result of modifications to the stream or watershed. Such changes may be the result of natural processes or human activities. The engineer must assess the present state of the stream and watershed and then evaluate potential future changes in the river system. From this assessment, the longterm streambed changes must be estimated. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-21 4 Roadway and Ballast 3.4.3 CONTRACTION SCOUR (2005) Contraction scour occurs when the flow area of a stream at flood stage is reduced, either by a natural contraction of the stream channel or by a bridge. It also occurs when overbank flow is forced back to the channel by railway embankments at the approaches to a bridge. From continuity, a decrease in flow area results in an increase in average velocity and bed shear stress through the contraction. Hence, there is an increase in erosive forces in the contraction and more bed material is removed from the contracted reach than is transported into the reach. This increase in transport of bed material from the reach lowers the natural bed elevation. As the bed elevation is lowered, the flow area increases and, in the riverine situation, the velocity and shear stress decrease until relative equilibrium is reached; i.e., the quantity of bed material that is transported into the reach is equal to that removed from the reach, or the bed shear stress is decreased to a value such that no sediment is transported out of the reach. Contraction scour, in a natural channel or at a bridge crossing, involves removal of material from the bed across all or most of the channel width and can occur as either clear-water or live-bed scour. Live-bed contraction scour is typically cyclic; for example, the bed scours during the rising stage of a runoff event and fills on the falling stage. The cyclic nature of contraction scour causes difficulties in determining contraction scour depths after a flood. The contraction of flow at a bridge can be caused by either a natural decrease in flow area of the stream channel or by abutments projecting into the channel and/or piers blocking a portion of the flow area. Contraction can also be caused by the approaches to a bridge cutting off floodplain flow. This can cause clear-water scour on a setback portion of a bridge section or a relief bridge because the floodplain flow does not normally transport significant concentrations of bed material sediments. This clearwater picks up additional sediment from the bed upon reaching the bridge opening. In addition, local scour at abutments may well be greater due to the clear-water floodplain flow returning to the main channel at the end of the abutment. Other factors that can cause contraction scour are (1) natural stream constrictions, (2) long railroad approaches to the bridge over the floodplain, (3) ice formations or jams, (4) natural berms along the banks due to sediment deposits, (5) debris, (6) vegetative growth in the channel or floodplain, and (7) pressure flow. 3.4.4 LOCAL SCOUR (2005) Local scour involves removal of material from around piers, abutments, spurs, and embankments. Local scour can be either clear-water or live-bed scour. The basic mechanism causing local scour at piers or abutments is the formation of vortices (known as the horseshoe vortex) at their base (Figure 1-3-5). The horseshoe vortex results from the pileup of water on the upstream surface of the obstruction and subsequent acceleration of the flow around the nose of the pier or abutment. The action of the vortex removes bed material from around the base of the obstruction. The transport rate of sediment away from the base region is greater than the transport rate into the region, and, consequently, a scour hole develops. As the depth of scour increases, the strength of the horseshoe vortex is reduced, thereby reducing the transport rate from the base region. Eventually, for livebed local scour, equilibrium is reestablished between bed material inflow and outflow and scouring ceases. For clear-water scour, scouring ceases when the shear stress caused by the horseshoe vortex equals the critical shear stress of the sediment particles at the bottom of the scour hole. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-22 AREMA Manual for Railway Engineering Natural Waterways Figure 1-3-5. Schematic Representation of Scour at a Cylindrical Pier 1 In addition to the horseshoe vortex around the base of a pier, there are vertical vortices downstream of the pier called the wake vortex (Figure 1-3-5). Both the horseshoe and wake vortices remove material from the pier base region. However, the intensity of wake vortices diminishes rapidly as the distance downstream of the pier increases. Therefore, immediately downstream of a long pier there is often deposition of material. Factors which affect the magnitude of local scour depth at piers and abutments are (1) velocity of the approach flow, (2) depth of flow, (3) width of the pier, (4) discharge intercepted by the abutment and returned to the main channel at the abutment (in laboratory flumes this discharge is a function of projected length of an abutment into the flow), (5) length of the pier if skewed to flow, (6) size and gradation of bed material, (7) angle of attack of the approach flow to a pier or abutment, (8) shape of a pier or abutment, (9) bed configuration, and (10) ice formation or jams and debris. 3 3.4.5 LATERAL STREAM MIGRATION (2005) 4 In addition to the types of scour mentioned above, naturally occurring lateral migration of the main channel of a stream within a floodplain may affect the stability of piers in a floodplain, erode abutments or the approach embankments, or change the total scour by changing the flow angle of attack at piers and abutments. Factors that affect lateral stream movement also affect the stability of a bridge foundation. Streams are dynamic. Areas of flow concentration continually shift banklines, and in meandering streams having an "S-shaped" planform, the channel moves both laterally and downstream. A braided stream has numerous channels which are continually changing. In a braided stream, the deepest natural scour occurs when two channels come together or when the flow comes together downstream of an island or bar. This scour depth has been observed to be 1 to 2 times the average flow depth. A bridge is static. It fixes the stream at one place in time and space. A meandering stream whose channel moves laterally and downstream into the bridge reach can erode the approach embankment and can affect © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-23 Roadway and Ballast contraction and local scour because of changes in flow direction. A braided stream can shift under a bridge and have two channels come together at a pier or abutment, increasing scour. Factors that affect lateral shifting of a stream and the stability of a bridge are the geomorphology of the stream, location of the crossing on the stream, flood characteristics, the characteristics of the bed and bank material, and wash load. It is difficult to anticipate when a change in planform may occur. It may be gradual or the result of a single major flood event. Also, the direction and magnitude of the movement of the stream are not easily predicted. While it is difficult to evaluate the vulnerability of a bridge due to changes in planform, it is important to incorporate potential planform changes into the design of new bridges and the design of countermeasures for existing bridges. Countermeasures for lateral shifting and instability of the stream may include changes in the bridge design, construction of river control works, protection of abutments with riprap, or careful monitoring of the river in a bridge inspection program. Serious consideration should be given to placing footings/foundations located on floodplains at elevations the same as those located in the main channel. Control of lateral shifting requires river training works, bank stabilizing by riprap, and/or guide banks. 3.4.6 TOTAL SCOUR (2005) Total scour at a railroad crossing is comprised of three components: (1) Long-term degradation of the river bed (2) Contraction scour at the bridge (3) Local scour at the piers or abutments These three scour components are added to obtain the total scour at a pier or abutment. This assumes that each component occurs independent of the other. Considering the components additive adds some conservatism to the design. In addition, lateral migration of the stream must be assessed when evaluating total scour at bridge piers and abutments. 3.4.7 REFERENCES FOR SECTION 3.4 (2005) Richardson, E.V. and Davis, S.R., 2001. "Evaluating Scour at Bridges," Fourth Edition, Report FHWA NHI 01001, Federal Highway Administration, Hydraulic Engineering Circular No. 18, U.S. Department of Transportation, Washington, D.C. Richardson, E.V., Simons, D.B., and Lagasse, P.F., 2001. "River Engineering for Highway Encroachments – Highways in the River Environment," Report FHWA NHI 01-004, Federal Highway Administration, Hydraulic Design Series No. 6, Washington, D.C. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-24 AREMA Manual for Railway Engineering Natural Waterways SECTION 3.5 CALCULATING SCOUR 3.5.1 PREDICTING AGGRADATION AND DEGRADATION (2005) 3.5.1.1 Long-Term Bed Elevation Changes Long-term bed elevation changes may be the natural trend of the stream or may be the result of some modification to the stream or watershed. The streambed may be aggrading, degrading, or in relative equilibrium in the vicinity of the bridge crossing. The problem for the engineer is to estimate the long-term bed elevation changes that will occur during the life of the structure. Factors that affect long-term bed elevation changes are dams and reservoirs (up- or downstream of the bridge), changes in watershed land use (urbanization, deforestation, etc.), channelization, cutoffs of meander bends (natural or man-made), changes in the downstream channel base level (control), gravel mining from the streambed, diversion of water into or out of the stream, natural lowering of the fluvial system, movement of a bend and bridge location with respect to stream planform, and stream movement in relation to the crossing. Tidal ebb and flood may degrade a coastal stream; whereas, littoral drift may result in aggradation. The elevation of the bed under bridges over a tributary to a larger stream will follow the trend of the larger stream unless there are controls. Controls could be bedrock, dams, culverts or other structures. The changes in bed elevation decrease the further upstream the bridge is from the confluence with another stream or from other bed elevation controls. The U.S. Army Corps of Engineers (USACE), U.S. Geological Survey (USGS), and other Federal and State agencies should be contacted concerning documented long-term streambed variations. If no data exist or if such data require further evaluation, an assessment of long-term streambed elevation changes for riverine streams should be made using the principles of river mechanics. Such an assessment requires the consideration of all influences upon the bridge crossing, i.e., runoff from the watershed to a stream (hydrology), sediment delivery to the channel (watershed erosion), sediment transport capacity of a stream (hydraulics), and response of a stream to these factors (geomorphology and river mechanics). Significant morphologic impacts can result from human activities. The assessment of the impact of human activities requires a study of the history of the river, as well as a study of present water and land use and stream control activities. 1 3 3.5.1.2 Estimating Long-Term Aggradation and Degradation The following sections outline procedures that can assist in identifying long-term trends in vertical stability. 4 Bridge Inspection Records The bridge inspection reports for railroad or highway bridges on the stream where a new or replacement bridge is being designed are an excellent source of data on long-term aggradation or degradation trends. Also, inspection reports for bridges crossing streams in the same area or region should be studied. Railroad bridges sometimes have records with a long history going back 100 years or more that document streambed conditions during original construction. For most highway bridges, the biannual inspection includes taking the elevation and/or cross section of the streambed under the bridge. These elevations are usually referenced to the bridge, but these relative bed elevations will show trends and can be referenced to sea level elevations. Successive cross sections from a series of bridges in a stream reach can be used to construct longitudinal streambed profiles through the reach. Gaging Station Records The USGS and many State Water Resource and Environmental agencies maintain gaging stations to measure stream flow. In the process they maintain records from which the aggradation or degradation of the streambed © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-25 Roadway and Ballast can be determined. Gaging station records at the bridge site, on the stream to be bridged and in the area or region can be used. Where an extended historical record is available, one approach to using gaging station records to determine long-term bed elevation change is to plot the change in stage through time for a selected discharge. This approach is often referred to as establishing a "specific gage" record. Figure 1-3-6 shows a plot of specific gage data for a discharge of 500 cfs from about 1910 to 1980 for Cache Creek in California. Cache Creek has experienced significant gravel mining with records of gravel extraction quantities available since about 1940. When the historical record of cumulative gravel mining is compared to the specific gage plot, the potential impacts are apparent. The specific gage record shows more than 10 ft of long-term degradation in a 70-year period. Figure 1-3-6. Specific Gage Data for Cache Creek, California Geology and Stream Geomorphology The geology and geomorphology of the site needs to be studied to determine the potential for long-term bed elevation changes at the bridge site. Quantitative techniques for streambed aggradation and degradation analyses are covered in detail in HEC-20. These techniques include: © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-26 AREMA Manual for Railway Engineering Natural Waterways • Incipient motion analysis • Analysis of armoring potential • Equilibrium slope analysis • Sediment continuity analysis Sediment transport concepts and equations are discussed in detail in HDS 6. Computer Models Sediment transport computer models can be used to determine long-term aggradation or degradation trends. These computer models route sediment down a channel and adjust the channel geometry to reflect imbalances in sediment supply and transport capacity. The BRI-STARS and HEC-6 models are examples of sediment transport models that can be used for single event or long-term estimates of changes in bed elevation. The information needed to run these models includes: • Channel and floodplain geometry • Structure geometry 1 • Roughness • Geologic or structural vertical controls • Downstream water surface relationship 3 • Event or long-term inflow hydrographs • Tributary inflow hydrographs • Bed material gradations • Upstream sediment supply 4 • Tributary sediment supply • Selection of appropriate sediment transport relationship • Depth of alluvium These models perform hydraulic and sediment transport computations on a cross section basis and adjust the channel geometry prior to proceeding with the next time step. The actual flow hydrograph can be used as input. Aggradation, Degradation, and Total Scour Using all the information available estimate the long-term bed elevation change at the bridge site for the design life of the bridge. Usually, the design life is 100 years. If the estimate indicates that the stream will degrade, use the elevation after degradation as the base elevation for contraction and local scour. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-27 Roadway and Ballast That is, total scour must include the estimated long-term degradation. If the estimate indicates that the stream will aggrade, then (1) make note of this fact to inspection and maintenance personnel, and (2) use existing ground elevation as the base for contraction and local scour. 3.5.2 PREDICTING LATERAL MIGRATION (2005) 3.5.2.1 Initiation of Meanders Although there is no completely satisfactory explanation of how or why meanders develop, it is known that meanders are initiated by localized bank retreat which alternates from one side of the channel to the other in a more or less regular pattern. The primary features of the flow pattern through meander bends are: • Superelevation of the water surface against the outside (convex) bank (Figure 1-3-7A) • Transverse current directed towards the outer bank at the surface and towards the inner bank at the bed producing a secondary circulation additional to the main downstream flow (Figure 1-3-7B) • Maximum-velocity current which moves from near the inner bank at the bend entrance to near the outer bank at the bend exit, crossing the channel at the zone of maximum bend curvature The transverse current and the primary downstream flow component combine to produce the helicoidal motion to the flow. The superelevation of the water surface against the outer bank of a bend produces a locally steep downstream energy gradient and, in turn, a zone of maximum boundary shear stress (b) in close proximity to the outer bank just downstream of the bend apex (Figure 1-3-7A). Secondary currents, which are usually weaker than primary ones, influence the distribution of velocity and boundary shear stress. The bend cross-section can be divided into three regions relative to the pattern of secondary flow (Figure 1-3-7B): • Mid-channel region, helicoidal flow is well established passing nearly 90 percent of the flow • Cell of opposite circulation develops in the outer bank region: the strength of this cell increases with discharge, the steepness of the bar, and the acuteness of the bend • Inner bank region where shoaling over the point bar induces a net outward flow, forcing the core of maximum velocity more rapidly toward the outer bank; increasing stage tends to reduce the shoaling, allowing an inward component of near-bed flow over the bar top The location and timing of the flow pattern varies with discharge, bend tightness, and cross-sectional form. Primary currents are dominant at high discharges because the main flow follows a straighter path, but secondary currents are relatively strong at intermediate discharges. The pattern of primary and secondary currents influences the distribution of erosion and deposition in meanders. In general, erosion in the bend is concentrated along the outer bank downstream of the bend apex where the currents are strongest, while point bar building predominates in a parallel position along the opposite bank, with material supplied by longitudinal and transverse currents. This produces a largely downvalley component to meander migration. 3.5.2.2 Evaluation and Prediction of Lateral Migration In general, most streams are sinuous to some degree and the majority of bank retreat and lateral migration occurs along meander bends. As such, the following discussion on evaluating and predicting lateral migration will focus on meander bends. One of the most practical methods for determining lateral stability and migration rates involves the analysis of sequential historic aerial photographs, maps, and surveys (Lagasse et al. 2003). © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-28 AREMA Manual for Railway Engineering Natural Waterways 1 Figure 1-3-7. Flow Patterns in Meanders (A) Location of maximum boundary shear stress (b), in a bend with a well-developed point bar (B) Secondary flow at a bend apex showing the outer bank cell and the shoaling-induced outward flow over the point bar. The most accurate means of measuring changes in channel geometry and lateral adjustments is through repetitive surveys of the channel cross section. However, this data is rarely available. The next easiest and relatively accurate method of determining migration rates and direction is through the comparison of sequential historical aerial photography (photos), maps, and surveys. Accuracy in such an analysis is greatly dependent on the period over which migration is evaluated, the amount and magnitude of internal and external perturbations forced on the system over time, and the number and quality of sequential aerial photos and maps. The analysis will be much more accurate for a channel that has coverage consisting of multiple data sets (aerial photos, maps, and surveys) covering a long period of time (several tens of years to more than 100 years) versus an analysis consisting of only two or three data sets covering a short time period (several years to a few tens of years). Predictions of migration for channels that have been extensively modified or have undergone major adjustments attributable to extensive land use changes will be much less reliable than those made for channels in relatively stable watersheds. Historical aerial photos and maps can be obtained from a number of federal, state, and local agencies (Lagasse et al. 2003). Extensive topographic map coverage of the United States at a variety of scales can be obtained from the local or regional offices of the U.S. Geological Survey. In general, both air photos and maps are required to perform a comprehensive and relatively accurate meander migration assessment. Since the scale of aerial photography is often approximate, contemporary maps are usually needed to accurately determine the true scale of air photos. Distortion of the image on aerial photos is also a common problem and becomes greater as one moves further away from the center of the photo. Expensive equipment, which is generally needed to rectify and eliminate aerial photo distortion, is often unavailable, so distortion and scale differences must be accounted for by some other means. The scale problem is easily rectified through the use of multiple distance measurements taken between common reference points on the photos and maps. The measurements of distance between several reference-point pairs common to both the photos and maps are then averaged to © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-29 3 4 Roadway and Ballast define an average scale for the photos. Common reference points can include cultural features such as building corners, roads or fences and their intersections, irrigation channels and canals, or natural features such as isolated rock outcrops, large boulders, and trees, drainages and stream confluences, and the irregular boundaries of water bodies. The accurate delineation of a bankline on aerial photos is primarily dependent on the density of vegetation at the top of the bank. Top bank is easily defined if stereo-pairs of photos are available. However, single photos can be used relatively easily if one knows what to look for. For banks with little or no vegetation, the top of the bank is easily identified. The abrupt change between the water and the top of the bank along the convex bank in a bend or an eroding cutbank is defined by an abrupt change in the contrast and color (color photo) or gray tone (black and white photo). Usually the water is significantly darker than the top of bank. Along the concave or inner bank of a bend, exposed bar sediment is lighter colored than the river or the top of bank. The top bank along a point bar is usually defined by persistent vegetation such as mature trees and shrubs. Where vegetation becomes increasingly dense along a bank, small sections of the top of the bank may be visible such that a line can be drawn connecting the sections. Often, the top of the bank may be completely obscured by vegetation and one may be required to locate the top of the bank by approximation. In this case, one can assume that the trunks of the largest trees growing along the river are nearly vertical and are located just landward of the top of the bank. Therefore, a line that approximates the top of the bank may be drawn just riverward of the center of the tree. The amount of error involved with this method increases with decreasing stream size. If the density of vegetation along a stream is such that an accurate delineation of the top of the bank cannot be made, then the use of the channel centerline may be required. The centerline is drawn with reference to bankfull conditions. Therefore, the channel centerline can and often does cross the exposed portions of point bars. Usually the channel centerline can be delineated more easily than a bankline masked by vegetation since the centerline can be drawn equidistant from the edge of mature vegetation on either side of the channel. There are three general methods of assessing lateral bank erosion and meander migration using maps and aerial photographs. The following discussion will deal with assessments using air photos, but the same methods can be used when making assessments or measurements from maps. In order of increasing complexity and accuracy, distances of lateral retreat can be: • Estimated by visual comparison of two air photos flown at different times • Measured by scaling distances directly from the bank to fixed reference points common to both photographs • Measured on a drawing on which historic channel banklines taken from sequential air photos are superimposed at the same scale The first method provides a preliminary assessment of stability, especially where significant changes in bank position have occurred. The second method requires measurements made along a line described by two reference points on either side of the bank that are common to both photos. The second method will usually only provide a few accurate measurements along the bank, depending on the number of reference points and the number of lines that can be drawn across the bend. Additional problems may be associated with the location of the lines since they may not be perpendicular to bank retreat nor allow a measurement at the point of maximum retreat. The third method is relatively easy and accurate. This method requires that the banklines and the common reference points from each historic air photo be traced onto a transparent or semi-transparent sheet after they have been enlarged or reduced to a common scale. The channel centerline can also be delineated on the same sheet at the same time. Then, each bankline or centerline is transferred to and superimposed on a common © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-30 AREMA Manual for Railway Engineering Natural Waterways sheet such that a sequential comparison of the banklines or centerlines can be made. The total bankline area eroded can be measured for each period and divided by the bankline length to define the average bank retreat. Dividing either the maximum distance or the average distance of bank retreat by the number of years between air photos results in a maximum or average migration rate, respectively. Drawing a line perpendicular to centerline at the location of maximum retreat defines the direction of maximum retreat. This process is repeated for each series of sequential photos. Based on the measurements between years, one may be able to define migration rates relative to significant hydrologic or geomorphic events. Overall rates can also be determined by summing the distances and dividing by the total number of years between the earliest and latest photos. 3.5.3 ESTIMATING CONTRACTION SCOUR (2005) 3.5.3.1 Contraction Scour Conditions Contraction scour equations are based on the principle of conservation of sediment transport (continuity). In the case of live-bed scour, the fully developed scour in the bridge cross section reaches equilibrium when sediment transported into the contracted section equals sediment transported out. As scour develops, the shear stress in the contracted section decreases as a result of a larger flow area and decreasing average velocity. For live-bed scour, maximum scour occurs when the shear stress reduces to the point that sediment transported in equals the bed sediment transported out and the conditions for sediment continuity are in balance. For clear-water scour, the transport into the contracted section is essentially zero and maximum scour occurs when the shear stress reduces to the critical shear stress of the bed material in the section. Normally, for both livebed and clear-water scour the width of the contracted section is constrained and depth increases until the limiting conditions are reached. 1 Live-bed contraction scour occurs at a bridge when there is transport of bed material in the upstream reach into the bridge cross section. With live-bed contraction scour the area of the contracted section increases until, in the limit, the transport of sediment out of the contracted section equals the sediment transported in. Clear-water contraction scour occurs when (1) there is no bed material transport from the upstream reach into the downstream reach, or (2) the material being transported in the upstream reach is transported through the downstream reach mostly in suspension and at less than capacity of the flow. With clear-water contraction scour the area of the contracted section increases until, in the limit, the velocity of the flow (V) or the shear stress (Jo) on the bed is equal to the critical velocity (Vc) or the critical shear stress (Jc) of a certain particle size (D) in the bed material. There are four conditions (cases) of contraction scour at bridge sites depending on the type of contraction, and whether there is overbank flow or relief bridges. Regardless of the case, contraction scour can be evaluated using two basic equations: (1) live-bed scour, and (2) clear-water scour. For any case or condition, it is only necessary to determine if the flow in the main channel or overbank area upstream of the bridge, or approaching a relief bridge, is transporting bed material (live-bed) or is not (clear-water), and then apply the appropriate equation with the variables defined according to the location of contraction scour (channel or overbank). To determine if the flow upstream of the bridge is transporting bed material, calculate the critical velocity for beginning of motion Vc of the D50 size of the bed material being considered for movement and compare it with the mean velocity V of the flow in the main channel or overbank area upstream of the bridge opening. If the critical velocity of the bed material is larger than the mean velocity (Vc > V), then clear-water contraction scour will exist. If the critical velocity is less than the mean velocity (Vc < V), then live-bed contraction scour will exist. To calculate the critical velocity use the following equation: Vc = Kuy1/6D1/3 EQ 11 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-31 3 4 Roadway and Ballast where: Vc = Critical velocity above which bed material of size D and smaller will be transported, m/s (ft/s) y = Average depth of flow upstream of the bridge, m (ft) D = Particle size for Vc, m (ft) D50 = Particle size in a mixture of which 50 percent are smaller, m (ft) Ku = 6.19 SI units Ku = 11.17 English units The D50 is taken as an average of the bed material size in the reach of the stream upstream of the bridge. It is a characteristic size of the material that will be transported by the stream. Normally this would be the bed material size in the upper 1 ft of the stream bed. Live-bed contraction scour depths may be limited by armoring of the bed by large sediment particles in the bed material or by sediment transport of the bed material into the bridge crosssection. Under these conditions, live-bed contraction scour at a bridge can be determined by calculating the scour depths using both the clear-water and live-bed contraction scour equations and using the smaller of the two depths. 3.5.3.2 Contraction Scour Cases Four conditions (cases) of contraction scour are commonly encountered: Case 1. Involves overbank flow on a floodplain being forced back to the main channel by the approaches to the bridge. Case 1 conditions include: a. The river channel width becomes narrower either due to the bridge abutments projecting into the channel or the bridge being located at a narrowing reach of the river (Figure 1-3-8); b. No contraction of the main channel, but the overbank flow area is completely obstructed by an embankment (Figure 1-3-9); or c. Abutments are set back from the stream channel (Figure 1-3-10). Case 2. Flow is confined to the main channel (i.e., there is no overbank flow). The normal river channel width becomes narrower due to the bridge itself or the bridge site is located at a narrower reach of the river (Figure 1-3-11 and Figure 1-3-12). Case 3. A relief bridge in the overbank area with little or no bed material transport in the overbank area (i.e., clear-water scour) (Figure 1-3-13). Case 4. A relief bridge over a secondary stream in the overbank area with bed material transport (similar to Case 1) (Figure 1-3-14). Notes: (1) Cases 1, 2, and 4 may either be live-bed or clear-water scour depending on whether there is bed material transport from the upstream reach into the bridge reach during flood flows. To determine if there is bed material transport compute the critical velocity at the approach section for the D50 of © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-32 AREMA Manual for Railway Engineering Natural Waterways the bed material using the equation given above and compare to the mean velocity at the approach section. To determine if the bed material will be washed through the contraction determine the ratio of the shear velocity (V*) in the contracted section to the fall velocity (T) of the D50 of the bed material being transported from the upstream reach (see the definition of V* in the live-bed contraction scour equation). If the ratio is much larger than 2, then the bed material from the upstream reach will be mostly suspended bed material discharge and may wash through the contracted reach (clear-water scour). (2) Case 1c is very complex. The depth of contraction scour depends on factors such as (1) how far back from the bank line the abutment is set, (2) the condition of the overbank (is it easily eroded, are there trees on the bank, is it a high bank, etc.), (3) whether the stream is narrower or wider at the bridge than at the upstream section, (4) the magnitude of the overbank flow that is returned to the bridge opening, and (5) the distribution of the flow in the bridge section, and (6) other factors. The main channel under the bridge may be live-bed scour; whereas, the set-back overbank area may be clear-water scour. WSPRO or HEC-RAS can be used to determine the distribution of flow between the main channel and the set-back overbank areas in the contracted bridge opening. However, the distribution of flow needs to be done with care. Studies by Chang and Sturm (HEC-18) have shown that conveyance calculations do not properly account for the flow distribution under the bridge. 1 3 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-33 Roadway and Ballast Figure 1-3-8. Case 1A: Abutments Project into Channel © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-34 AREMA Manual for Railway Engineering Natural Waterways 1 3 4 Figure 1-3-9. Case 1B: Abutments at Edge of Channel © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-35 Roadway and Ballast Figure 1-3-10. Case 1C: Abutments Set Back from Channel © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-36 AREMA Manual for Railway Engineering Natural Waterways 1 3 4 Figure 1-3-11. Case 2A: River Narrows © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-37 Roadway and Ballast Figure 1-3-12. Case 2B: Bridge Abutments and/or Piers Constrict Flow © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-38 AREMA Manual for Railway Engineering Natural Waterways 1 Figure 1-3-13. Case 3: Relief Bridge Over Floodplain 3 4 Figure 1-3-14. Case 4: Relief Bridge Over Secondary Stream © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-39 Roadway and Ballast If the abutment is set back only a small distance from the bank (less than 3 to 5 times the average depth of flow through the bridge), there is the possibility that the combination of contraction scour and abutment scour may destroy the bank. Also, the two scour mechanisms are not independent. Consideration should be given to using a guide bank and/or protecting the bank and bed under the bridge in the overflow area with rock riprap. See Section 3.6 for guidance on designing rock riprap. (3) Case 3 may be clear-water scour even though the floodplain bed material is composed of sediments with a critical velocity that is less than the flow velocity in the overbank area. The reasons for this are (1) there may be vegetation growing part of the year, and (2) if the bed material is fine sediments, the bed material discharge may go into suspension (wash load) at the bridge and not influence contraction scour. (4) Case 4 is similar to Case 3, but there is sediment transport into the relief bridge opening (live-bed scour). This case can occur when a relief bridge is over a secondary channel on the floodplain. Hydraulically this is no different from Case 1, but analysis is required to determine the floodplain discharge associated with the relief opening and the flow distribution going to and through the relief bridge. This information could be obtained from WSPRO or HEC-RAS. 3.5.3.3 Live-Bed Contraction Scour A modified version of Laursen's 1960 equation for live-bed scour at a long contraction is recommended to predict the depth of scour in a contracted section. The equation assumes that bed material is being transported from the upstream section. y2 ⎛ Q2 ⎞ =⎜ ⎟ y1 ⎝ Q 1 ⎠ 6 /7 ⎛ W1 ⎞ ⎜ ⎟ ⎝ W2 ⎠ k1 EQ 12 ys = y2 - yo = (average contraction scour depth) EQ 13 where: y1 = Average depth in the upstream main channel, m (ft) y2 = Average depth in the contracted section,m (ft) yo = Existing depth in the contracted section before scour, m (ft) (see Note 7) Q1 = Flow in the upstream channel transporting sediment, m3/s (ft3/s) Q2 = Flow in the contracted channel, m3/s (ft3/s) W1 = Bottom width of the upstream main channel that is transporting bed material, m (ft) W2 = Bottom width of the main channel in the contracted section less pier width(s), m (ft) k1 = Exponent determined below V*/ T k1 Mode of Bed Material Transport <0.50 0.59 Mostly contact bed material discharge 0.50 to 2.0 0.64 Some suspended bed material discharge >2.0 0.69 Mostly suspended bed material discharge © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-40 AREMA Manual for Railway Engineering Natural Waterways V* = ((gy1S1)1/2, shear velocity in the upstream section, m/s (ft/s) Fall velocity of bed material based on the D50, m/s (Figure 1-3-15) g = Acceleration of gravity (9.81 m/s2) (32.2 ft/s2) S1 = Slope of energy grade line of main channel, m/m (ft/ft) Shear stress on the bed, Pa (N/m2) (lb/ft2) Density of water (1000 kg/m3) (1.94 slugs/ft3) Notes: (1) Q2 may be the total flow going through the bridge opening as in cases 1a and 1b. It is not the total flow for Case 1c. For Case 1c contraction scour must be computed separately for the main channel and the left and/or right overbank areas. (2) Q1 is the flow in the main channel upstream of the bridge, not including overbank flows. (3) W1 and W2 are not always easily defined. In some cases, it is acceptable to use the topwidth of the main channel to define these widths. Whether topwidth or bottom width is used, it is important to be consistent so that W1 and W2 refer to either bottom widths or top widths. 1 3 4 Figure 1-3-15. Fall Velocity of Sand-sized Particles with Specific Gravity of 2.65 in Metric Units (4) The average width of the bridge opening (W2) is normally taken as the bottom width, with the width of the piers subtracted. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-41 Roadway and Ballast (5) Laursen's equation will overestimate the depth of scour at the bridge if the bridge is located at the upstream end of a natural contraction or if the contraction is the result of the bridge abutments and piers. At this time, however, it is the best equation available. (6) In sand channel streams where the contraction scour hole is filled in on the falling stage, the y0 depth may be approximated by y1. Sketches or surveys through the bridge can help in determining the existing bed elevation. (7) Scour depths with live-bed contraction scour may be limited by coarse sediments in the bed material armoring the bed. Where coarse sediments are present, it is recommended that scour depths be calculated for live-bed scour conditions using the clear-water scour equation (given in the next section) in addition to the live-bed equation, and that the smaller calculated scour depth be used. 3.5.3.4 Clear-Water Contraction Scour The recommended clear-water contraction scour equation is: EQ 14 EQ 15 ys = y2 - yo = (average contraction scour depth) where: y2 = Average equilibrium depth in the contracted section after contraction scour, m (ft) yo = Average existing depth in the contracted section, m (ft) Q = Discharge through the bridge or on the set-back overbank area at the bridge associated with the width W, m3/s (ft3/s) Dm = Diameter of the smallest nontransportable particle in the bed material (1.25 D50) in the contracted section, m (ft) D50 = Median diameter of bed material, m (ft) W = Bottom width of the contracted section less pier widths, m (ft) Ku = 0.025 SI units Ku= 0.0077 English units EQ 14 is a rearranged version of EQ 11. Because D50 is not the largest particle in the bed material, the scoured section can be slightly armored. Therefore, the Dm is assumed to be 1.25 D50. For stratified bed material the depth of scour can be determined by using the clear-water scour equation sequentially with successive Dm of the bed material layers. 3.5.3.5 Contraction Scour With Backwater The live-bed contraction scour equation is derived assuming a uniform reach upstream and a long contraction into a uniform reach downstream of the bridge. With live-bed scour the equation computes a depth after the © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-42 AREMA Manual for Railway Engineering Natural Waterways long contraction where the sediment transport into the downstream reach is equal to the sediment transport out. The clear-water contraction scour equations are derived assuming that the depth at the bridge increases until the shear-stress and velocity are decreased so that there is no longer any sediment transport. With the clear-water equations it is assumed that flow goes from one uniform flow condition to another. Both equations calculate contraction scour depth assuming a level water surface (ys = y2 -yo). A more consistent computation would be to write an energy balance before and after the scour. For live-bed the energy balance would be between the approach section (1) and the contracted section (2). Whereas, for clear-water scour it would be the energy at the same section before (1) and after (2) the contraction scour. Backwater, in extreme cases, can decrease the velocity, shear stress and the sediment transport in the upstream section. This will increase the scour at the contracted section. The backwater can, by storing sediment in the upstream section, change live-bed scour to clear-water scour. 3.5.4 ESTIMATING LOCAL PIER SCOUR (2005) 3.5.4.1 General Local scour at piers is a function of bed material characteristics, bed configuration, flow characteristics, fluid properties, and the geometry of the pier and footing. The bed material characteristics are granular or non granular, cohesive or noncohesive, erodible or non erodible rock. Granular bed material ranges in size from silt to large boulders and is characterized by the D50 and a coarse size such as the D84 or D90 size. Cohesive bed material is composed of silt and clay, possibly with some sand which is bonded chemically. Rock may be solid, massive, or fractured. It may be sedimentary or igneous and erodible or non erodible. Flow characteristics of interest for local pier scour are the velocity and depth just upstream of the pier, the angle the velocity vector makes to the pier (angle of attack), and free surface or pressure flow. Fluid properties are viscosity, and surface tension which for the field case can be ignored. Pier geometry characteristics are its type, dimensions, and shape. Types of piers include single column, multiple columns, or rectangular; with or without friction or tip bearing piles; with or without a footing or pile cap; footing or pile cap in the bed, on the surface of the bed, in the flow or under the deck out of the flow. Important dimensions are the diameter for circular piers or columns, spacing for multiple columns, and width and length for solid piers. Shapes include round, square or sharp nose, circular cylinder, group of cylinders, or rectangular. In addition, piers may be simple or complex. A simple pier is a single shaft, column or multiple columns exposed to the flow. Whereas, a complex pier may have the pier, footing or pile cap, and piles exposed to the flow. Local scour at piers has been studied extensively in the laboratory; however, there is limited field data. The laboratory studies have been mostly of simple piers, but there have been some laboratory studies of complex piers. Often the studies of complex piers are model studies of actual or proposed pier configurations. As a result of the many laboratory studies, there are numerous pier scour equations. In general, the equations are for livebed scour in cohesionless sand-bed streams. A graphical comparison of the more common equations is given in Figure 1-3-16. Some of the equations have velocity as a variable, normally in the form of a Froude Number. However, some equations, such as Laursen's do not include velocity. A Froude Number of 0.3 was used in Figure 1-3-16 for purposes of comparing commonly used scour equations. Based on a comparison of the equations with the laboratory data and available field data, the Colorado State University (CSU) equation is recommended to estimate pier scour. 3.5.4.2 Local Pier Scour Equation To determine pier scour, an equation based on the CSU equation is recommended for both live-bed and clearwater pier scour. The equation predicts maximum pier scour depths. The equation is: © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-43 1 3 4 Roadway and Ballast EQ 16 Figure 1-3-16. Comparison of Scour Equations for Variable Depth Ratios (y/a) (HEC-18) As a Rule of Thumb, the maximum scour depth for round nose piers aligned with the flow is: ys = 2.4 times the pier width (a) for Fr 0.8 EQ 17 ys = 3.0 times the pier width (a) for Fr > 0.8 In terms of ys/a, EQ 16 is: EQ 18 where: ys = Scour depth, m (ft) y1 = Flow depth directly upstream of the pier, m (ft) K1 = Correction factor for pier nose shape from Figure 1-3-17 and Table 1-3-10 K2 = Correction factor for angle of attack of flow from Table 1-3-11 or EQ 19 K3 = Correction factor for bed condition from Table 1-3-12 a = Pier width, m (ft) © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-44 AREMA Manual for Railway Engineering Natural Waterways L = Length of pier, m (ft) Fr1 = Froude Number directly upstream of the pier = V1/(gy1)1/2 V1 = Mean velocity of flow directly upstream of the pier, m/s (ft/s) g = Acceleration of gravity (9.81 m/s2) (32.2 ft/s2) The correction factor, K2, for angle of attack of the flow, , is calculated using the following equation: EQ 19 If L/a is larger than 12, use L/a = 12 as a maximum in EQ 19 and Table 1-3-11. Table 1-3-11 illustrates the magnitude of the effect of the angle of attack on local pier scour. 1 Figure 1-3-17. Common Pier Shapes 3 Table 1-3-10. Correction Factor, K1, for Pier Nose Shape Shape of Pier Nose K1 (a) Square nose 1.1 (b) Round nose 1.0 (c) Circular cylinder 1.0 (d) Group of cylinders 1.0 (e) Sharp nose 0.9 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-45 Roadway and Ballast Table 1-3-11. Correction Factor, K2, for Angle of Attack, , of the Flow Angle L/a=4 L/a=8 L/a=12 0 1.0 1.0 1.0 15 1.5 2.0 2.5 30 2.0 2.75 3.5 45 2.3 3.3 4.3 90 2.5 3.9 5.0 Angle = skew angle of flow L = length of pier Table 1-3-12. Increase in Equilibrium Pier Scour Depths, K3, for Bed Condition Bed Condition Dune Height m K3 Clear-Water Scour N/A 1.1 Plane bed and Antidune flow N/A 1.1 Small Dunes 3 > H > 0.6 1.1 Medium Dunes 9>H>3 1.2 to 1.1 Large Dunes H>9 1.3 Notes: (1) The correction factor K1 for pier nose shape should be determined using Table 1-3-10 for angles of attack up to 5 degrees. For greater angles, K2 dominates and K1 should be considered as 1.0. If L/a is larger than 12, use the values for L/a = 12 as a maximum in Table 1-3-11 and EQ 19. (2) The values of the correction factor K2 should be applied only when the field conditions are such that the entire length of the pier is subjected to the angle of attack of the flow. Use of this factor will result in a significant over-prediction of scour if (1) a portion of the pier is shielded from the direct impingement of the flow by an abutment or another pier; or (2) an abutment or another pier redirects the flow in a direction parallel to the pier. For such cases, judgment must be exercised to reduce the value of the K2 factor by selecting the effective length of the pier actually subjected to the angle of attack of the flow. EQ 19 should be used for evaluation and design. Table 1-3-11 is intended to illustrate the importance of angle of attack in pier scour computations and to establish a cutoff point for K2 (i.e., a maximum value of 5.0). (3) The correction factor K3 results from the fact that for plane-bed conditions, which is typical of most bridge sites for the flood frequencies employed in scour design, the maximum scour may be 10 percent greater than computed with Equation 3.6. In the unusual situation where a dune bed configuration with large dunes exists at a site during flood flow, the maximum pier scour may be 30 percent greater than the predicted equation value. This may occur on very large rivers, such as the Mississippi. For smaller streams that have a dune bed configuration at flood flow, the dunes will be smaller and the maximum scour may be only 10 to 20 percent larger than equilibrium scour. For antidune bed configuration the maximum scour depth may be 10 percent greater than the computed equilibrium pier scour depth (see HDS 6). (4) Piers set close to abutments (for example at the toe of a spill through abutment) must be carefully evaluated for the angle of attack and velocity of the flow coming around the abutment. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-46 AREMA Manual for Railway Engineering Natural Waterways 3.5.4.3 Scour for Complex Pier Foundations Most pier scour research has focused on solid piers with limited attention to determining scour depths for (1) pile groups, (2) pile groups and pile caps, or (3) pile groups, pile caps and solid piers exposed to the flow. In the general case, the flow could be obstructed by three substructure elements (scour-producing components), which include the pier stem, the pile cap or footing, and the pile group. Reference to FHWA's HEC-18 is suggested for methods and equations to determine scour depths for complex pier foundations. 3.5.4.4 Multiple Columns Skewed to the Flow For multiple columns (illustrated as a group of cylinders in Figure 1-3-18) skewed to the flow, the scour depth depends on the spacing between the columns. The correction factor for angle of attack would be smaller than for a solid pier. Raudkivi in discussing effects of alignment states "...the use of cylindrical columns would produce a shallower scour; for example, with five-diameter spacing the local scour can be limited to about 1.2 times the local scour at a single cylinder." In application of EQ 16 with multiple columns spaced less than 5 pier diameters apart, the pier width 'a' is the total projected width of all the columns in a single bent, normal to the flow angle of attack (Figure 1-3-18). For example, three 2.0 m (6.6 ft) cylindrical columns spaced at 10.0 m (33 ft) would have an 'a' value ranging between 2.0 and 6.0 m (6.6 and 33 ft), depending upon the flow angle of attack. This composite pier width would be used in EQ 16 to determine depth of pier scour. The correction factor K1 in EQ 16 for the multiple column would be 1.0 regardless of column shape. The coefficient K2 would also be equal to 1.0 since the effect of skew would be accounted for by the projected area of the piers normal to the flow. 1 3 4 Figure 1-3-18. Multiple Columns Skewed to the Flow The scour depth for multiple columns skewed to the flow can also be determined by determining the K2 factor using EQ 19 and using it in EQ 16. The width "a" in EQ 16 would be the width of a single column. If the multiple columns are spaced 5 diameter or greater apart; and debris is not a problem, limit the scour depths to a maximum of 1.2 times the local scour of a single column. The depth of scour for a multiple column bent will be analyzed in this manner except when addressing the effect of debris lodged between columns. If debris is evaluated, it would be logical to consider the multiple columns and debris as a solid elongated pier. The appropriate L/a value and flow angle of attack would then be used to determine K2 in EQ 19. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-47 Roadway and Ballast 3.5.4.5 Scour From Debris on Piers Debris (or ice) lodged on a pier can increase local scour at a pier. The debris may increase pier width and deflect a component of flow downward. This increases the transport of sediment out of the scour hole. When floating debris or ice is lodged on the pier, the scour depth can be estimated by assuming that the pier width is larger than the actual width. The problem is in determining the increase in pier width to use in the pier scour equation. At large depths, the effect of the debris or ice on scour depth should diminish. Debris and ice effects on contraction scour can also be accounted for by estimating the amount of flow blockage (decrease in width of the bridge opening) in the equations for contraction scour. Limited field measurements of scour at ice jams indicate the scour can be as much as 10 to 30 ft. 3.5.4.6 Topwidth of Scour Holes The topwidth of a scour hole in cohesionless bed material from one side of a pier or footing can be estimated from the following equation: EQ 20 where: W = Topwidth of the scour hole from each side of the pier or footing, m (ft) ys = Scour depth, m (ft) K = Bottom width of the scour hole related to the depth of scour Angle of repose of the bed material ranging from about 30 to 44 The angle of repose of cohesionless material in air ranges from about 30× to 44×. Therefore, if the bottom width of the scour hole is equal to the depth of scour ys (K = 1), the topwidth in cohesionless sand would vary from 2.07 to 2.80 ys. At the other extreme, if K = 0, the topwidth would vary from 1.07 to 1.8 ys. Thus, the topwidth could range from 1.0 to 2.8 ys and depends on the bottom width of the scour hole and composition of the bed material. In general, the deeper the scour hole, the smaller the bottom width. In water, the angle of repose of cohesionless material is less than the values given for air; therefore, a topwidth of 2.0 ys is suggested for practical applications (Figure 1-3-19). © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-48 AREMA Manual for Railway Engineering Natural Waterways Figure 1-3-19. Topwidth of Scour Hole 1 3.5.5 EVALUATING LOCAL SCOUR AT ABUTMENTS (2005) 3.5.5.1 General Scour occurs at abutments when the abutment and embankment obstruct the flow. Several causes of abutment failures during post-flood field inspections of bridge sites have been documented: 3 • Overtopping of abutments or approach embankments • Lateral channel migration or stream widening processes • Contraction scour 4 • Local sour at one or both abutments Abutment damage is often caused by a combination of these factors. Where abutments are set back from the channel banks, especially on wide floodplains, large local scour holes have been observed with scour depths of as much as four times the approach flow depth on the floodplain. As a general rule, the abutments most vulnerable to damage are those located at or near the channel banks. The flow obstructed by the abutment and approach railroad embankment forms a horizontal vortex starting at the upstream end of the abutment and running along the toe of the abutment, and a vertical wake vortex at the downstream end of the abutment (Figure 1-3-20). © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-49 Roadway and Ballast Figure 1-3-20. Schematic Representation of Abutment Scour Figure 1-3-21. Scour of Bridge Abutment and Approach Embankment The vortex at the toe of the abutment is very similar to the horseshoe vortex that forms at piers, and the vortex that forms at the downstream end is similar to the wake vortex that forms downstream of a pier. Research has been conducted to determine the depth and location of the scour hole that develops for the horizontal (so called horseshoe) vortex that occurs at the upstream end of the abutment, and numerous abutment scour equations have been developed to predict this scour depth. Abutment failures and erosion of the fill also occur from the action of the downstream wake vortex. However, research and the development of methods to determine the erosion from the wake vortex has not been conducted. An example of abutment and approach erosion of a bridge due to the action of the horizontal and wake vortex is shown in Figure 1-3-21. The types of failures described above are initiated as a result of the obstruction to the flow caused by the abutment and railroad embankment and subsequent contraction and turbulence of the flow at the abutments. There are other conditions that develop during major floods, particularly on wide floodplains, that are more difficult to foresee but that need to be considered in the hydraulic analysis and design of the substructure: © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-50 AREMA Manual for Railway Engineering Natural Waterways • Gravel pits on the floodplain upstream of a structure can capture the flow and divert the main channel flow out of its normal banks into the gravel pit. This can result in an adverse angle of attack of the flow on the downstream embankment with subsequent breaching of the embankment and/ or failure of the abutment. • Levees can become weakened and fail with resultant adverse flow conditions at the bridge abutment. • Debris can become lodged at piers and abutments and on the bridge superstructure, modifying flow conditions and creating adverse angles of attack of the flow on bridge piers and abutments. 3.5.5.2 Designing for Scour at Abutments The preferred design approach is to place the abutment foundation on scour resistant rock or on deep foundations. Present technology has not developed sufficiently to provide reliable abutment scour estimates for all hydraulic flow conditions that might be reasonably expected to occur at an abutment. Therefore, engineering judgment is required in designing foundations for abutments. In many cases, foundations can be designed with shallower depths than predicted by the equations when they are protected with rock riprap and/or with a guide bank placed upstream of the abutment. The potential for lateral channel migration, long-term degradation and contraction scour should be considered in setting abutment foundation depths near the main channel. It is recommended that the abutment scour equations presented in this section be used to develop insight as to the scour potential at an abutment. 1 3.5.5.3 Abutment Conditions Abutments can be set back from the natural stream bank, placed at the bankline or, in some cases, actually set into the channel itself. Common designs include stub abutments placed on spill-through slopes, and vertical wall abutments, with or without wingwalls. Scour at abutments can be live-bed or clear-water scour. The bridge and approach embankment can cross the stream and floodplain at a skew angle and this will have an effect on flow conditions at the abutment. Finally, there can be varying amounts of overbank flow intercepted by the approaches to the bridge and returned to the stream at the abutment. More severe abutment scour will occur when the majority of overbank flow returns to the bridge opening directly upstream of the bridge crossing. Less severe abutment scour will occur when overbank flows gradually return to the main channel upstream of the bridge crossing. 3.5.5.4 Abutment Skew 4 The skew angle for an abutment (embankment) is depicted in Figure 1-3-22. For an abutment angled downstream, the scour depth is decreased, whereas the scour depth is increased for an abutment angled upstream. 3.5.5.5 Abutment Shape There are three general shapes of abutments: (1) spill-through abutments, (2) vertical walls without wing walls, and (3) vertical-wall abutments with wing walls (Figure 1-3-23). These shapes have varying angles to the flow. As shown in Table 1-3-13, depth of scour is approximately double for vertical-wall abutments as compared with spill-through abutments. Similarly, scour at vertical wall abutments with wingwalls is reduced to 82 percent of the scour of vertical wall abutments without wingwalls. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 3 1-3-51 Roadway and Ballast Figure 1-3-22. Orientation of Embankment Angle, , to the Flow Figure 1-3-23. Abutment Shape Table 1-3-13. Abutment Shape Coefficients Description K1 Vertical-wall abutment 1.00 Vertical-wall abutment with wing walls 0.82 Spill-through abutment 0.55 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-52 AREMA Manual for Railway Engineering Natural Waterways 3.5.5.6 Live-Bed Scour at Abutments An equation based on field data of scour at the end of spurs in the Mississippi River (obtained by the USACE) can be used for estimating abutment scour. This field situation closely resembles the laboratory experiments for abutment scour in that the discharge intercepted by the spurs was a function of the spur length. The modified equation, is applicable when the ratio of projected abutment (embankment) length (L) to the flow depth (y1) is greater than 25. This equation can be used to estimate scour depth (ys) at an abutment where conditions are similar to the field conditions from which the equation was derived: EQ 21 where: ys = Scour depth, m (ft) y1 = Depth of flow at the abutment on the overbank or in the main channel, m (ft) Fr = Froude Number based on the velocity and depth adjacent to and upstream of the abutment L = Length of embankment projected normal to the flow m (ft) K1 = Abutment shape coefficient (from Table 1-3-13) K2 = Coefficient for angle of embankment to flow 1 K2 = (see Figure 1-3-22 for definition of if embankment points downstream if embankment points upstream For cases where the abutment (embankment) length is small in comparison to flow depth (L/y1 25), the following equation for local live-bed scour can be used to estimate abutment scour at a stable spill slope when the flow is subcritical: 3 EQ 22 Where the variables are defined as for EQ 21. EQ 21 and EQ 22 are recommended for both live-bed and clearwater abutment scour conditions. 3.5.6 TOTAL SCOUR CALCULATION PROBLEM (2005) Figure 1-3-24 shows a cross section plot of a railroad crossing a small stream. The bridge is 50 feet long with vertical abutments and a single pier in the channel. The left and right abutments are set back 10 and 15 feet from the channel banks, respectively. The rectangular pier is 1.5 feet wide by 12 feet long and is located in the center of the bridge but not in the center of the channel. The channel bed and floodplain material is a silty sand with a median grain size, D50, equal to 0.20 mm (0.00066 ft). Figure 1-3-25 shows the channel, floodplain and railroad crossing in plan and includes the hydraulic data required for contraction scour calculations in the channel and overbank areas under the bridge. Figure 1-3-26 shows the hydraulic data for computing pier and abutment scour. Assume zero and eight degree angles of attack for the pier scour computation. The flow data are from a hydraulic analysis of the crossing for the design discharge of 1000 cfs. The railroad grade is at an elevation of 13.0 ft, the bridge low chord is at an elevation of 10.0 ft, the water surface at the crossing is at © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-53 4 Roadway and Ballast elevation 8.5 ft, the floodplain is at elevation of 5.0 ft and the channel invert is at an elevation of -0.9 ft. The crossing causes 0.5 feet of backwater at the cross section upstream of the bridge (water surface equals 9.0 feet). Figure 1-3-24. Cross Section for Total Scour Problem © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-54 AREMA Manual for Railway Engineering Natural Waterways 1 3 Figure 1-3-25. Hydraulic Data for Contraction Scour Calculations 4 3.5.6.1 Main Channel Contraction Scour Determine if the upstream channel flow is live-bed or clear-water by comparing the average channel velocity to the critical velocity for 0.20 mm sand. Average channel velocity V = Q1/A = 700 / (25.0 x 9.0) = 3.1 ft/s Critical velocity (EQ 11) Vc = Kuy1/6D1/3 = 11.17 (9.0)1/6 (0.00066)1/3 = 1.4 ft/s © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-55 Roadway and Ballast The channel flow velocity is greater than the critical velocity for the bed material and the channel contraction scour is live-bed. Determine k1 for the live-bed contraction scour equation. Compute the ratio of shear velocity (V*) to particle fall velocity ( from Figure 1-3-15) to determine the mode of bed material transport and k1. V* = (gy1S1)1/2 = (32.2 x 9.0 x 0.00035)1/2 = 0.32 ft/s = 0.025 m/s = 0.082 ft/s V*/ = 0.32 / 0.082 = 3.9 The ratio of shear velocity to fall velocity is greater than 2.0 and the mode of bed material transport is mostly suspended. Therefore k1 = 0.69. Live-bed contraction scour (EQ 12 and EQ 13) ys = y2 - y0 = 11.2 - 8.5 = 2.7 ft 3.5.6.2 Right overbank contraction scour Assume that the overbank contraction scour is clear water. This assumption can be checked by comparing the upstream floodplain flow velocity (V = 0.38 ft/s) to the critical velocity (Vc = 1.2 ft/s). Clear-water contraction scour (EQ 14 and EQ 15) Dm = 1.25D50 = 1.25 x 0.00066 = 0.00083 ft ys = y2 - y0 = 4.8 - 3.5 = 1.3 ft 3.5.6.3 Left overbank contraction scour ys = y2 - y0 = 3.1 - 3.5 = -0.4 ft (actually 0.0 ft) Negative clear-water scour indicates that there is insufficient velocity to cause erosion in the overbank area under the bridge. Therefore, the there is no contraction scour on the left overbank. Sediment will not deposit in the left overbank area under the bridge because there is no sediment in transport from the floodplain upstream (clear-water upstream floodplain flow). © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-56 AREMA Manual for Railway Engineering Natural Waterways Figure 1-3-26. Hydraulic Data for Local Scour Calculations 1 3.5.6.4 Pier Scour Pear Scour for zero degree angle of attack (EQ 16) Although the pier is not in the center of the channel, use the maximum channel velocity since the channel has the potential to migrate laterally. The pier shape is square end (K1 = 1.1), the angle of attack is 0 degrees (K2 = 1.0), and the bed condition is small dunes or plane bed (K3 = 1.1). 3 4 Pier scour for 8 degree angle of attack (EQ 16 and EQ 19) The pier shape is not included because angle of attack is greater than 5 degrees (K1 = 1.0), the angle of attack is 8 degrees (K2 = 1.5 from Table 1-3-11 for 8 degrees and L/a = 12/1.5 = 8 or use EQ 19), and the bed condition is small dunes or plane bed (K3 = 1.1). K2 = (Cos + (L / a) Sin )0.65 = (Cos 8 + (12 / 1.5) Sin 8)0.65 = 1.6 Note: The difference between Table 1-3-11 and EQ 19 is due to linear interpolation and rounding when using the table. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-57 Roadway and Ballast 3.5.6.5 Right Abutment Scour Check the ratio of embankment length (L) to flow depth at the abutment (y1) to determine which equation is applicable. L / y1 = 105 / 3.5 = 30 > 25. Use EQ 21. Abutment shape is vertical-wall (K1 = 1.0) and the embankment is perpendicular to flow ( = 90, K2 = 1.0). For deep abutment scour, protect the abutment with riprap (Article 3.6.4.2). Also consider using a spill through slope to reduce scour to 8.0 ft and provide riprap protection. 3.5.6.6 Left Abutment Scour Check the ratio of embankment length (L) to flow depth at the abutment (y1) to determine which equation is applicable. L / y1 = 70 / 3.5 = 20 < 25. Use EQ 22. Abutment shape is vertical-wall (K1 = 1.0) and the embankment is perpendicular to flow ( = 90, K2 = 1.0). For deep abutment scour, protect the abutment with riprap (Article 3.6.4.2). Also consider using a spill through slope to reduce scour to 6.0 ft and provide riprap protection. 3.5.6.7 Plot Total Scour The total scour is the sum of long-term degradation, contraction and local scour. Figure 1-3-27 shows the contraction and local scour plotted in the bridge cross section. If long-term degradation is expected, then it should be included in the main channel prior contraction and local scour. If the channel could migrate laterally, then the maximum scour can occur at piers located in the overbank areas. The local scour hole side slopes are shown at a 1.25H:1V slope due to the cohesive channel bed and floodplain materials. The abutment scour could be eliminated with well designed riprap and the abutment scour could be substantially reduced if the abutment included a spill-through slope. However, the spill-through slope would reduce also bridge open area. The channel pier should be designed for the maximum potential scour. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-58 AREMA Manual for Railway Engineering Natural Waterways 1 Figure 1-3-27. Total Scour Plot 3 3.5.7 REFERENCES FOR SECTION 3.5 (2005) Arneson, L.A. and Shearman, J.O., 1998. "User's Manual for WSPRO – A Computer Model for Water Surface Profile Computations," Office of Technology Applications, Federal Highway Administration, FHWA Report No. FHWA-SA-98-080. Lagasse, P.F., Schall, J.D., and Richardson, E.V., 2001. "Stream Stability at Highway Structures," Hydraulic Engineering Circular No. 20, Third Edition, FHWA NHI 01-002, Federal Highway Administration, Washington, D.C. Lagasse, P.F., Spitz, W.J., Zevenbergen, L.W., and Zachmann, D.W., 2003. "Handbook for Predicting Stream Meander Migration Using Aerial Photographs and Maps," Ayres Associates for the National Cooperative Highway Research Program, Transportation Research Board, National Research Council, Washington, D.C. Molinas, A., 1990. "Bridge Stream Tube Model for Alluvial River Simulation" (BRI-STARS), User's Manual, National Cooperative Highway Research Program, Project No. HR15-11, Transportation Research Board, Washington, D.C. Richardson, E.V. and Davis, S.R., 2001. "Evaluating Scour at Bridges," Fourth Edition, Report FHWA NHI 01001, Federal Highway Administration, Hydraulic Engineering Circular No. 18, U.S. Department of Transportation, Washington, D.C. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-59 4 Roadway and Ballast Richardson, E.V., Simons, D.B., and Lagasse, P.F., 2001. "River Engineering for Highway Encroachments – Highways in the River Environment," Report FHWA NHI 01-004, Federal Highway Administration, Hydraulic Design Series No. 6, Washington, D.C. U.S. Army Corps of Engineers, 1993. "Scour and Deposition in Rivers and Reservoirs," User's Manual, HEC-6, Hydrologic Engineering Center, Davis, CA. U.S. Army Corps of Engineers, 2001. "River Analysis System," HEC-RAS, Hydraulic Reference Manual Version 3.0, Hydrologic Engineering Center, Davis, CA. SECTION 3.6 PROTECTING ROADWAY AND BRIDGES FROM SCOUR Adequate protection against floods and washouts is essential not only for maintenance of dependable service, but also to avoid heavy expenditures to replace damaged facilities and restore operation. 3.6.1 EMBANKMENT (2005) 3.6.1.1 General – Risks and Possible Damage Water overflowing the embankment, either from a direct flow or backwater, frequently results in damage to the railroad. This damage may be as severe as a washout or less apparent in other forms, such as, a loss of the shoulder, a steepening of the embankment, a loss of crib or shoulder ballast, or a softening of the subgrade's support characteristics. Damage resulting from sloughing and slides is usually more severe as the water recedes from a saturated embankment. Loose, fine-grained, cohesionless soils are more susceptible to sloughing. In general, soil conditions, vegetation, and the rapidity at which the water recedes are primary factors in determining the risk of sloughing. 3.6.1.2 Temporary Protection Measures Temporary protection of the railway embankment section is sometimes necessary, particularly in flood events where immediate action is necessary and time constraints do not permit implementation of a permanent solution. Periodic and close track inspections of flood and washout susceptible areas and identification of high risk locations will be a beneficial first step in determining the appropriate remedial repair. Temporary protection of potential overflow slopes and fill sections subject to erosion and sloughing can be provided by placement of an armor of heavy weight material, not easily displaced by floodwaters, such as largesized stone (riprap) or sandbags. In blanketing the slopes, it is critical that the toe be adequately protected to minimize the risk of base scour and possible embankment failure. Raising the embankment shoulder with riprap and sandbags can also be a suitable means for temporary relief. 3.6.1.3 Permanent Protection Measures In overflow territories, care must be taken to review the adequacy of design, location and construction of existing drainageways and make appropriate corrections if deficiencies are found. Sufficient waterway capacity is essential to minimize heading during floods and, if necessary, provisions should be made for additional relief openings to handle the flow. The impact of runoff from neighboring facilities, existing and proposed, must also be assessed. Input from applicable local, state, or federal authorities should be sought in these preliminary drainage assessments. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-60 AREMA Manual for Railway Engineering Natural Waterways Selection of the optimal permanent protection measure should be done on a site-specific basis and will depend on many factors, including service requirements, severity and extent of the damage potential, embankment soil characteristics, and economic considerations. A subsurface exploration of the area in question, performed during the preliminary stages, can many times generate valuable information and aid in the selection and design process. In general, depending upon service requirements, a track raise is the best assurance for reliable operation. Embankments subject to severe side erosion can be protected by relocation of the track and/or channel, or construction of revetments as discussed in Article 3.6.4.5. In overflow bottoms where either a channel change, installation of additional openings, or a track raise or relocation do not afford sufficient relief, consideration should be given to facing the downstream side of the embankments at least at critical locations with riprap or other suitable means of protection. Covering erosion-susceptible slopes with a thick vegetative cover can furthermore provide protection by impeding surface erosion. On light traffic density lines where the aforementioned extensive measures cannot be economically justified, consideration might be given to anchoring the track to the roadbed, at designated locations throughout the overflow area, utilizing cable tied to rail, timber pile, screw anchors driven in the roadbed or hot asphalt impregnated ballast. Under these conditions use of a heavy course ballast tends to reduce the incidence of ballast displacement. When using this last method of protection, the railroad is accepting the risk of traffic disruption due to flooding and washouts. 3.6.2 BRIDGES (2005) 1 3.6.2.1 General – Risks and Possible Damage Protection against flood damage for structures calls for resourcefulness during the immediate flooding threat, as well as during the implementation of permanent protection measures. Temporary measures should be given consideration to prevent both minor and major damage. Minor damage can be categorized as scour on the shoulders or behind the abutments, debris hung up in the waterway opening, overtopping, and various other damage that can be immediately detected and repaired. Major damage includes items such as contamination of ballast decks and track beds, scouring around piling, piers, foundations, and backwalls; channel changes resulting in silting or bypassing the structure; culvert piping or joint separation; etc. 3 3.6.2.2 Temporary Protection Measures The need for temporary protection should be considered not only prior to and during floods, but also when the structure is under construction. Temporary measures to consider during or immediately preceding a flood include, identification of high-risk areas, frequent inspection, remove or pass debris through the structure to avoid accumulation, and the placement of riprap or sandbags. The following are temporary measures to be considered when the structure is in the design or construction stage; all the measures considered previously, and others such as fence jetties, rock jetties, and channel cutoffs. 3.6.2.3 Permanent Protection Measures Permanent protection measures require that sound engineering principles be employed to protect the structure from flood damage and allow its continued function as designed. Bridges and culverts must be designed with sufficient waterway opening to handle the design storm. In addition, both structures must be designed with an adequate opening to pass the anticipated debris. When conditions change in the upstream basin, some of the measures detailed in various articles in Article 3.6.4 may need to be incorporated in the structure protection plan. Permanent protection might also include underwater or other inspections of potential problem areas. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-61 4 Roadway and Ballast 3.6.3 COUNTERMEASURE SELECTION (2005) 3.6.3.1 General A countermeasure is defined as a measure incorporated into a stream crossing system to monitor, control, inhibit, change, delay, or minimize stream and bridge stability problems (HEC-23). Countermeasures may be installed at the time of railroad construction or retrofitted to resolve stability problems at existing crossings. Retrofitting is good economics and good engineering practice in many locations because the magnitude, location, and nature of potential stability problems are not always discernible at the design stage, and indeed, may take a period of several years to develop. A countermeasure does not need to be a separate structure, but may be an integral part of the roadbed. For example, relief bridges on floodplains are countermeasures which alleviate scour from flow contraction at the bridge over the stream channel. Some features that are integral to the railroad design serve as countermeasures to minimize stream stability problems. Abutments and piers oriented with the flow reduce local scour and contraction scour. Also, reducing the number of piers and/or setting back the abutments reduces contraction scour. Countermeasures which are not integral to the embankment may serve one function at one location and a different function at another. For example, bank revetment may be installed to control bank erosion from meander migration, or it may be used to stabilize streambanks in the contracted area at a bridge. Other countermeasures are useful for one function only. This category of countermeasures includes spurs constructed in the stream channel to control meander migration. A countermeasure matrix (Table 1-3-14) has been developed which lists most countermeasures presently in use for stream instability and scour problems and summarizes river environmental factors that influence the selection of a countermeasure for a specific problem (HEC-23). In selecting a countermeasure it is necessary to evaluate how the stream might respond to the countermeasure, and also how the stream may respond as the result of the activities of other parties. 3.6.3.2 Overview of the Countermeasure Matrix A wide variety of countermeasures have been used to control channel instability and scour at bridge foundations. The countermeasure matrix, presented in Table 1-3-14, is organized to highlight the various groups of countermeasures and to identify their individual characteristics. The left column of the matrix lists types of countermeasures in groups. In each row of the matrix, distinctive characteristics of a particular countermeasure are identified. The matrix identifies most countermeasures in use today and lists information on their functional applicability to a particular problem, their suitability to specific river environments, the general level of maintenance resources required, and which states have experience with specific countermeasures. Finally, a reference source for design guidelines is noted, where available. Countermeasures have been organized into groups based on their functionality with respect to scour and stream instability. The three main groups of countermeasures are: hydraulic countermeasures, structural countermeasures and monitoring. The following outline identifies the countermeasure groups in the matrix: Group 1. Hydraulic Countermeasures • Group 1.A: River training structures – Transverse structures – Longitudinal structures © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-62 AREMA Manual for Railway Engineering Natural Waterways – Areal structures • Group 1.B: Armoring countermeasures – Revetment and Bed Armor • Rigid • Flexible/articulating – Local armoring Group 2. Structural Countermeasures • Foundation strengthening • Pier geometry modification Group 3. Monitoring • Fixed Instrumentation • Portable instrumentation 1 • Visual Monitoring 3.6.3.3 Countermeasure Groups Group 1. Hydraulic Countermeasures Hydraulic countermeasures are those which are primarily designed either to modify the flow or resist erosive forces caused by the flow. Hydraulic countermeasures are organized into two groups: river training structures and armoring countermeasures. The performance of hydraulic countermeasures is dependent on design considerations such as filter requirements and edge treatment. Group 1.A River Training Structures. River training structures are those which modify the flow. River training structures are distinctive in that they alter hydraulics to mitigate undesirable erosional and/or depositional conditions at a particular location or in a river reach. River training structures can be constructed of various material types and are not distinguished by their construction material, but rather, by their orientation to flow. River training structures are described as transverse, longitudinal or areal depending on their orientation to the stream flow. • Transverse river training structures are countermeasures which project into the flow field at an angle or perpendicular to the direction of flow. • Longitudinal river training structures are countermeasures which are oriented parallel to the flow field or along a bankline. • Areal river training structures are countermeasures which cannot be described as transverse or longitudinal when acting as a system. This group also includes countermeasure "treatments" which have areal characteristics such as channelization, flow relief, and sediment detention. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-63 3 4 Roadway and Ballast 1-3-64 Table 1-3-14. Stream Instability and Bridge Scour Countermeasures Matrix AREMA Manual for Railway Engineering © 2010, American Railway Engineering and Maintenance-of-Way Association © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering Table 1-3-14. Stream Instability and Bridge Scour Countermeasures Matrix (Continued) Natural Waterways 1-3-65 Roadway and Ballast Group 1.B Armoring Countermeasures. Armoring countermeasures are distinctive because they resist the erosive forces caused by a hydraulic condition. Armoring countermeasures do not necessarily alter the hydraulics of a reach, but act as a resistant layer to hydraulic shear stresses providing protection to the more erodible materials underneath. Armoring countermeasures generally do not vary by function, but vary more in material type. Armoring countermeasures are classified by two functional groups: revetments and bed armoring or local scour armoring. • Revetments and bed armoring are used to protect the channel bank and/or bed from erosive/hydraulic forces. They are usually applied in a blanket type fashion for areal coverage. Revetments and bed armoring can be classified as either rigid or flexible/articulating. Rigid revetments and bed armoring are typically impermeable and do not have the ability to conform to changes in the supporting surface. These countermeasures often fail due to undermining. Flexible/ articulating revetments and bed armoring can conform to changes in the supporting surface and adjust to settlement. These countermeasures often fail by removal and displacement of the armor material. • Local scour armoring is used specifically to protect individual substructure elements of a bridge from local scour. Generally, the same material used for revetments and bed armoring is used for local armoring, but these countermeasures are designed and placed to resist local vortices created by obstructions to the flow. Group 2. Structural Countermeasures Structural countermeasures involve modification of the bridge structure (foundation) to prevent failure from scour. Typically, the substructure is modified to increase bridge stability after scour has occurred or when a bridge is assessed as scour critical. These modifications are classified as either foundation strengthening or pier geometry modifications. • Foundation strengthening includes additions to the original structure which will reinforce and/or extend the foundations of the bridge. These countermeasures are designed to prevent failure when the channel bed is lowered to an expected scour elevation, or to restore structural integrity after scour has occurred. Design and construction of bridges with continuous spans provide redundancy against catastrophic failure due to substructure displacement as a result of scour. Retrofitting a simple span bridge with continuous spans could also serve as a countermeasure after scour has occurred or when a bridge is assessed as scour critical. • Pier geometry modifications are used to either reduce local scour at bridge piers or to transfer scour to another location. These modifications are used primarily to minimize local scour. Group 3. Monitoring Monitoring describes activities used to facilitate early identification of potential scour problems. Monitoring could also serve as a continuous survey of the scour progress around the bridge foundations. Monitoring allows for action to be taken before the safety of the railroad is threatened by the potential failure of a bridge. Monitoring can be accomplished with instrumentation or visual inspection. A well designed monitoring program can be a very cost-effective countermeasure. Two types of instrumentation are used to monitor bridge scour: fixed instruments and portable instruments. • Fixed instrumentation describes monitoring devices which are attached to the bridge structure to detect scour at a particular location. Typically, fixed monitors are located at piers and abutments. The number and location of piers to be instrumented should be defined, as it may be impractical to place a fixed instrument at every pier and abutment on a bridge. Instruments such as sonar monitors can be used to provide a timeline of scour, whereas instruments such as magnetic sliding collars can only be © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-66 AREMA Manual for Railway Engineering Natural Waterways used to monitor the maximum scour depth. Data from fixed instruments can be downloaded manually at the site or it can be telemetered to another location. • Portable instrumentation describes monitoring devices that can be manually carried and used along a bridge and transported from one bridge to another. Portable instruments are more cost effective in monitoring an entire bridge than fixed instruments; however, they do not offer a continuous watch over the structure. The allowable level of risk will affect the frequency of data collection using portable instruments. • Visual inspection describes standard monitoring practices of inspecting the bridge on a regular interval and increasing monitoring efforts during high flow events (flood watch). Typically, bridges are inspected on an annual schedule. Where stream stability is questionable, channel bed elevations at each pier location can be recorded during the annual inspection. The channel bed elevations should be compared with historical cross sections to identify changes in bed elevations due to degradation or lateral migration. Channel elevations should also be taken during and after high flow events. If measurements cannot be safely collected during a high flow event, the engineer should determine if the bridge is at risk and if train operation restrictions are necessary. Underwater inspections of the foundations could be used to supplement the visual inspection after a flood. 3.6.3.4 Countermeasure Characteristics The countermeasure matrix (Table 1-3-14) was developed to identify distinctive characteristics for each type of countermeasure. Five categories of countermeasure characteristics were defined to aid in the selection and implementation of countermeasures: 1 • Functional Applications • Suitable River Environment • Maintenance 3 • Installation/Experience by State • Design Guidelines Reference These categories were used to answer the following questions: 4 • For what type of problem is the countermeasure applicable? • In what type of river environment is the countermeasure best suited or, are there river environments where the countermeasure will not perform well? • What level of resources will need to be allocated for maintenance of the countermeasure? • What states or regions in the U.S. have experience with this countermeasure? • Where do I obtain design guidance reference material? Functional Applications The functional applications category describes the type of scour or stream instability problem for which the countermeasure is prescribed. The five main categories of functional applications are local scour at abutments and piers, contraction scour, and vertical and lateral instability. Vertical instability implies the long-term processes of aggradation or degradation over relatively long river reaches, and lateral instability involves a © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-67 Roadway and Ballast long-term process of channel migration and bankline erosion problems. To associate the appropriate countermeasure type with a particular problem, filled circles, half circles and open circle are used in the matrix as described below: n well suited/primary use - the countermeasure is well suited for the application; the countermeasure has a good record of success for the application; the countermeasure was implemented primarily for this application. n possible application/secondary use - the countermeasure can be used for the application; the countermeasure has been used with limited success for the application; the countermeasure was implemented primarily for another application but also can be designed to function for this application. In addition, this symbol can identify an application for which the countermeasure has performed successfully and was implemented primarily for that application, but there is only a limited amount of data on its performance and therefore the application cannot be rated as well suited. unsuitable/rarely used - the countermeasure is not well suited for the application; the countermeasure has a poor record of success for the application; the countermeasure was not intended for this application. N/A not applicable - the countermeasure is not applicable to this functional application. Suitable River Environment This category describes the characteristics of the river environment for which a given countermeasure is best suited or under which there would be a reasonable expectation of success. Conversely, this category could indicate conditions under which experience has shown a countermeasure may not perform well. The river environment characteristics that can have a significant effect on countermeasure selection or performance are: • River type • Stream size (width) • Bend radius • Flow velocity • Bed material • Ice/debris load • Bank condition • Floodplain (width) © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-68 AREMA Manual for Railway Engineering Natural Waterways For each environmental characteristic, a qualitative range is established (e.g., stream size: Wide, Moderate, or Small) to serve as a suitability discriminator. While most characteristics are self explanatory, both HEC-20 ("Stream Stability at Highway Structures") and HDS 6 ("River Engineering for Highway Encroachments") provide guidance on the range and definitions of these characteristics of the river environment. In the context of this matrix, the bank condition characteristic (Vertical, Steep, or Flat) considers the effectiveness of a given countermeasure to protect a bank with that configuration, not the suitability for installation of the countermeasure on a bank with that configuration. Where a block is checked for a given countermeasure under an environmental characteristic, the countermeasure is considered suitable or has been applied successfully for the full range of that environmental characteristic. The checked block means that the characteristic does not influence the selection of the countermeasure, i.e., the countermeasure is suitable for the full range of that characteristic. For example, guide banks have been applied successfully in braided, meandering, and straight streams; however, bendway weirs/stream barbs are most suitable for installation on meandering streams. Maintenance The maintenance category identifies the estimated level of maintenance that may need to be allocated to service the countermeasure. The ratings in this category range from "Low" to "High" and are subjective. The ratings represent the relative amount of resources required for maintenance with respect to other countermeasures within the matrix shown in Table 1-3-14. A low rating indicates that the countermeasure is relatively maintenance free, a moderate rating indicates that some maintenance is required, and a high rating indicates that the countermeasure requires more maintenance than most of the countermeasures in the matrix. 1 Installation/Experience by State Departments of Transportation This category identifies states (or a region) where a particular countermeasure has been installed. These listings may not include all of the states which have used a particular countermeasure. Certain countermeasures are used in many states. These countermeasures have a listing of "Widely Used" in this category. Both successful, and unsuccessful experiences are reflected by the listing. 3 Design Guideline Reference Reference manuals which provide guidance in countermeasure design have been developed by government agencies through research programs. The FHWA has produced a wealth of information through the federally coordinated program of highway research and development. The design guideline reference column identifies reference manuals where guidance on design of the countermeasures can be obtained. The references are symbolized by numbers in this column. The numbers correspond to the numbers of the references listed on the second page of the matrix. Countermeasures for which design guidelines are provided in HEC-23 are referenced using DG#, where # represents a number assigned to the design guideline (see also Section 3.6.4). 3.6.3.5 Summary The countermeasures matrix is convenient reference guide on a wide range of countermeasures applicable to scour and stream stability problems. An engineering plan to install countermeasures should provide conceptual design and cost information on several alternative countermeasures, with a recommended alternative based on a variety of engineering, environmental and cost factors. The countermeasures matrix is a good way to begin identifying and prioritizing possible alternatives. The information provided in the matrix related to functional applications, suitable river applications and maintenance issues should facilitate preliminary selection of feasible alternatives prior to more detailed investigation. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-69 4 Roadway and Ballast 3.6.3.6 Selection of Countermeasures for Stream Instability The selection of an appropriate countermeasure for a specific bank erosion problem is dependent on factors such as the erosion mechanism, stream characteristics, construction and maintenance requirements, potential for vandalism, and costs. Perhaps more important, however, is the effectiveness of the measure selected in performing the required function. Protection of an existing bank line may be accomplished with revetments, spurs, retardance structures, longitudinal dikes, or bulkheads (Table 1-3-14). Spurs, longitudinal dikes, and area retardance structures can be used to establish a new flow path and channel alignment, or to constrict flow in a channel. Because of their high cost, bulkheads may be appropriate for use only where space is at a premium. Channel relocation may be used separately or in conjunction with other countermeasures to change the flow path and flow orientation. Erosion Mechanism Bank erosion mechanisms are surface erosion and/or mass wasting. Surface erosion is the removal of soil particles by the velocity and turbulence of the flowing water. Mass wasting is by slides, rotational slip, piping and block failure. In general slides, rotational slip and block failure result from the bank being undercut by the flow. Also, seepage force of the pore water in the bank is another factor that can cause surface erosion or mass wasting. The type of mechanism is determined by the magnitude of the erosive forces of the water, type of bed and bank material, vegetation, and bed elevation stability of the stream. Stream Characteristics Stream characteristics that influence the selection of countermeasures include (see also Table 1-3-14): • Channel width • Bank height • Channel configuration • Channel material • Vegetative cover • Sediment transport condition • Bend radii • Channel velocities and flow depth • Ice and debris • Floodplain characteristics Channel Width. Channel width influences the use of bendway weirs and other spur-type countermeasures. On smaller streams (<250 feet wide), flow constriction resulting from the use of spurs may cause erosion of the opposite bank. However, spurs can be used on small channels where the purpose is to shift the location of the channel. Bank Height. Low banks (<10 feet) may be protected by any of the countermeasures, including bulkheads. Medium height banks (from 10 to 20 feet) may be protected by revetment, retardance structures, spurs, and longitudinal dikes. High banks (>20 feet) generally require revetments used alone or in conjunction with other measures. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-70 AREMA Manual for Railway Engineering Natural Waterways Channel Configuration. Spurs and jack fields have been successfully used as a countermeasure to control the location of the channel in meandering and braided streams. Also, bulkheads, revetments, and riprap have been used to control bank erosion resulting from stream migration. On anabranching streams, revetments, riprap, and spurs have been used to control bank erosion and channel shifting. Also, channels that do not carry large flows can and have been closed off. Channel Material. Spurs, revetments, riprap, jack fields, or check dams can be used in any type of channel material if they are designed correctly. However, jack fields should only be placed on streams that carry appreciable debris and sediment in order for the jacks to cause deposition and eventually be buried. Bank Vegetation. Vegetation such as willows can enhance the performance of structural countermeasures and may, in some cases, reduce the level of structural protection needed. Meander migration and other bank erosion mechanisms are accelerated on many streams in reaches where vegetation has been cleared. Sediment Transport. The sediment transport conditions can be described as regime, threshold, or rigid. Regime channel beds are those which are in motion under most flow conditions, generally in sand or silt-size noncohesive materials. Threshold channel beds have no bed material transport at normal flows, but become mobile at higher flows. They may be cut through cohesive or noncohesive materials, and an armor layer of coarse-grained material can develop on the channel bed. Rigid channel beds are cut through rock or boulders and rarely or never become mobile. In general, permeable structures will cause deposition of bed material in transport and are better suited for use in regime and some threshold channels than in rigid channel conditions. Impermeable structures are more effective than permeable structures in channels with little or no bed load, but impermeable structures can also be very effective in mobile bed conditions. Revetments can be effectively used with mobile or immobile channel beds. Bend Radii. Bend radii affect the design of countermeasures, because some countermeasures will only function properly in long or moderate radius bends. Thus, the cost per meter (foot) of bank protection provided by a specific countermeasure may differ considerably between short-radius and longer radius bends. 1 Channel Velocities and Flow Depth. Channel hydraulics affect countermeasure selection because structural stability and induced scour must be considered. Some of the permeable flow retardance measures may not be structurally stable and countermeasures which utilize piles may be susceptible to scour failure in high velocity environments. Ice and Debris. Ice and debris can damage or destroy countermeasures and should always be considered during the selection process. On the other hand, the performance of some permeable spurs and area retardance structures is enhanced by debris where debris accumulation induces additional sediment deposition. Floodplains. In selecting countermeasures for stream stability and scour, the amount of flow on the floodplain is an important factor. For example, if there is appreciable overbank flow, then the use of guide banks to protect abutments should be considered. Also, spurs perpendicular to the approach embankment may be required to control erosion. Construction and Maintenance Requirements Standard requirements regarding construction or maintenance such as the availability of materials, construction equipment requirements, site accessibility, time of construction, contractor familiarity with construction methods, and a program of regular maintenance, inspection, and repair are applicable to the selection of appropriate countermeasures. Additional considerations for countermeasures located in stream channels include: constructing and maintaining a structure that may be partially submerged at all times, the extent of bank disturbance which may be necessary, and the desirability of preserving streambank vegetative cover to the extent practicable. Vandalism Vandalism is always a maintenance concern since effective countermeasures can be made ineffective by vandals. Documented vandalism includes dismantling of devices, burning, and cutting or chopping with knives, wire cutters, and axes. Countermeasure selection or material selection for construction may be affected by concerns of vandalism. For example, rock-filled baskets (gabions) may not be appropriate in some urban environments. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-71 3 4 Roadway and Ballast Costs Cost comparisons should be used to study alternative countermeasures with an understanding that the measures were installed under widely varying stream conditions, that the conservatism (or lack thereof) of the designer is not accounted for, that the relative effectiveness of the measures cannot be quantitatively evaluated, and that some measures included in the cost data may not have been fully tested by floods. 3.6.3.7 Countermeasures for Meander Migration The best countermeasure against meander migration is to locate the bridge crossing on a relatively straight reach of stream between bends. At many such locations, countermeasures may not be required for several years because of the time required for the bend to move to a location where it becomes a threat to the railroad facility. However, bend migration rates on other streams may be such that countermeasures will be required after a few years or a few flood events and, therefore, should be installed during initial construction. Stabilizing channel banks at a railroad stream crossing can cause a change in the channel cross section and an increase in stream sinuosity upstream of the stabilized banks. Figure 1-3-28a illustrates a natural channel section in a bend with the deeper section at the outside of the bend and a gentle slope toward the inside bank resulting from point bar growth. Figure 1-3-28b illustrates the scour which results from stabilizing the outside bank of the channel and the resulting steeper slope of the point bar on the inside of the bend. This effect must be considered in the design of the countermeasure and the bridge. It should also be recognized that the thalweg location and flow direction can change as sinuosity upstream increases. Countermeasures for meander migration include those that: • Protect an existing bank line • Establish a new flow line or alignment • Control and constrict channel flow The classes of countermeasures identified for bank stabilization and bend control are bank revetments, spurs, retardance structures, longitudinal dikes, vane dikes, bulkheads, and channel relocations. Also, a carefully planned cutoff may be an effective way to counter problems created by meander migration. These measures may be used individually or in combination to combat meander migration at a site. Some of these countermeasures are also applicable to bank erosion from causes other than bend migration. Figure 1-3-28. Comparison of Channel Bend Cross Sections (a) for Natural Conditions, and (b) for Stabilized Bend (after Brown) © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-72 AREMA Manual for Railway Engineering Natural Waterways 3.6.3.8 Countermeasures for Channel Braiding and Anabranching Channel braiding occurs in streams with an overload of sediment, causing deposition and aggradation. As aggradation occurs, the slope of the channel increases, velocities increase, and multiple, interconnected channels develop. The overall channel system becomes wider and multiple channels are formed as bars of sediment are deposited in the main channel (see HEC-20 or HDS 6). Braiding can also occur where banks are easily eroded and there is a large range in discharge. The channel becomes wider at high flows, and low-flow forms multiple interconnected channels. In an anabranched stream, flow is divided by islands rather than bars, and the anabranched channels are more permanent than braided channels and generally convey more flow. Braided channels change alignment rapidly, and are very wide and shallow even at flood flow. They present problems at bridge sites because of the high cost of bridging the complete channel system, unpredictable channel locations and flow directions, difficulties with eroding channel banks, and in maintaining bridge openings unobstructed by bars and islands. Countermeasures used on braided and anabranched streams are usually intended to confine the multiple channels to one channel. This tends to increase the sediment transport capacity in the principal channel and encourage deposition in secondary channels. These measures usually consist of dikes constructed from the margins of the braided zone to the channel over which the bridge is constructed. Guide banks at bridge abutments (see Article 3.6.4.3) in combination with revetment on embankment fill slopes (see Article 3.6.4.5), riprap on embankment fill slopes only, and spurs (see Article 3.6.4.4) arranged in the stream channels to constrict flow to one channel have also been used successfully. 1 Since anabranches are permanent channels that may convey substantial flow, diversion and confinement of an anabranched stream is likely to be more difficult than for a braided stream. The designer may be faced with a choice of either building more than one bridge, building a long bridge, or diverting anabranches into a single channel. 3.6.3.9 Countermeasures for Degradation and Aggradation 3 Bed elevation instability problems are common on alluvial streams. Degradation in streams can cause the loss of bridge piers in stream channels and can contribute to the loss of piers and abutments located on caving banks. Aggradation causes the loss of waterway opening in bridges and, where channels become wider because of aggrading streambeds, overbank piers and abutments can be undermined. At its worst, aggradation may cause streams to abandon their original channels and establish new flow paths which could isolate the existing bridge. Countermeasures to Control Degradation Countermeasures used to control bed degradation include check dams and channel linings. Check-dams and structures which perform functions similar to check-dams include drop structures, cutoff walls, and drop flumes. A check-dam is a low dam or weir constructed across a channel to prevent upstream degradation (see Article 3.6.4.7). Channel linings of concrete and riprap have proved unsuccessful at stopping degradation. To protect the lining, a check-dam may have to be placed at the downstream end to key it to the channel bed. Such a scheme would provide no more protection than would a check dam alone, in which case the channel lining would be redundant. Bank erosion is a common hydraulic hazard in degrading streams. As the channel bed degrades, bank slopes become steeper and bank caving failures occur. The USACE found that longitudinal stone dikes, or rock toe-dikes, provided the most effective toe protection of all bank stabilization measures studied for very dynamic and/or actively degrading channels. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-73 4 Roadway and Ballast Countermeasures to Control Aggradation Currently, measures used in attempts to alleviate aggradation problems include channelization, debris basins, bridge modification, and/or continued maintenance, or combinations of these. Channelization may include dredging and clearing channels, constructing small dams to form debris basins, constructing cutoffs to increase the local slope, constructing flow control structures to reduce and control the local channel width, and constructing relief channels to improve flow capacity at the crossing. Except for debris basins and relief channels, these measures are intended to increase the sediment transport capacity of the channel, thus reducing or eliminating problems with aggradation. Cutoffs must be designed with considerable study as they can cause erosion and degradation upstream and deposition downstream (see Article 3.6.4.8). The most common bridge modifications are increasing the bridge length by adding spans and increasing the effective flow area beneath the structure by raising the bridge deck. A program of continuing maintenance has been successfully used to control problems at bridges on aggrading streams. In such a program, a monitoring system is set up to survey the affected crossing at regular intervals. When some pre-established deposition depth is reached, the bridge opening is dredged or cleared of the deposited material. In some cases, this requires opening a clearing after every major flood. This solution requires surveillance and dedication to the continued maintenance of an adequate waterway under the bridge. Otherwise, it is only a temporary solution. A debris basin or a deeper channel upstream of the bridge may be easier to maintain. Continuing maintenance is not recommended if analysis shows that other countermeasures are practicable. 3.6.3.10 Selection of Countermeasures for Scour at Bridges The selection of an appropriate countermeasure for scour at a bridge requires an understanding of the erosion mechanism producing the specific scour problem. For example, contraction scour results from a sediment imbalance across most or all of the channel while local scour at a pier or abutment results from the action of vortices at an obstruction to the flow. Degradation is a component of total scour, but is considered a channel instability problem. 3.6.3.11 Countermeasures for Contraction Scour Severe contraction of flow at railroad stream crossings has resulted in numerous bridge failures at abutments, approach fills, and piers from contraction scour. Design alternatives to decrease contraction scour include longer bridges, relief bridges on the floodplain, and superstructures at elevations above flood stages of extreme events. These design alternatives are integral features of the facility which reduce the contraction at bridges and, therefore, reduce the magnitude of contraction scour. The elevation of bridge superstructures is recognized as important to the integrity of the bridge because of hydraulic forces that may damage the superstructure. These include buoyancy and impact forces from ice and other floating debris. Contraction scour is another consideration in setting the superstructure elevation. When the superstructure of a bridge becomes submerged or when ice or debris lodged on the superstructure causes the flow to contract, flow may be accelerated and more severe scour can occur. For this reason, where contraction scour is of concern, bridge superstructures should be located with clearance for debris, and, if practicable, above the stage of floods larger than the design flood. Similarly, pier design, span length, and pier location can become more important contributors to contraction scour where debris can lodge on the piers and further contract flow in the waterway. In streams which carry heavy loads of debris, longer, higher spans and solid piers will help to reduce the collection of debris. Where practicable, piers should be located out of the main current in the stream, i.e., outside the thalweg at high flow. There are numerous locations where piers occupy a significant area in the stream channel and contribute to contraction scour. The principal countermeasure used for reducing the effects of contraction is revetment on channel banks and fill slopes at bridge abutments (see Article 3.6.4.5). However, guide banks may be used to reduce the effects of contraction by moving the site of local scour caused by the turbulence of intersecting flows and contraction away from the bridge abutment (see Article 3.6.4.3). © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-74 AREMA Manual for Railway Engineering Natural Waterways The potential for undesired effects from stabilizing all or any portion of the channel perimeter at a contraction should be considered. Stabilization of the banks may only result in exaggerated scour in the streambed near the banks or, in a relatively narrow channel, across the entire channel. Stabilization of the streambed may also result in exaggerated lateral scour in any size stream. Stabilization of the entire stream perimeter may result in downstream scour or failure of some portion of the countermeasures used on either the streambed or banks. 3.6.3.12 Countermeasures for Local Scour Local scour occurs in bridge openings at piers and abutments. In general, design alternatives against structural failure from local scour consist of measures which reduce scour depth, such as pier shape and orientation, and measures which retain their structural integrity after scour reaches its maximum depth, such as placing foundations in sound rock and using deep piling. Countermeasures which can reduce the risk from scour include riprap. Abutments Countermeasures for local scour at abutments consist of measures which improve flow orientation at the bridge end and move local scour away from the abutment, as well as revetments and riprap placed on spill slopes to resist erosion. Guide banks are earth or rock embankments placed at abutments. Flow disturbances, such as eddies and cross-flow, will be eliminated where a properly designed and constructed guide bank is placed at a bridge abutment. Guide banks also protect the railroad embankment, reduce local scour at the abutment and adjacent piers, and move local scour to the end of the guide bank (see Article 3.6.4.3). 1 Local scour also occurs at abutments as a result of expanding flow downstream of the bridge, especially for bridges on wide, wooded floodplains that have been cleared for construction of the railroad. Short guide banks extending downstream of the abutment to the tree line will move this scour away from the abutment, and the trees will retard velocities so that flow redistribution can occur with minimal scour. Revetments may consist of pervious rock or rigid concrete. Rock riprap revetment provides an effective countermeasure against erosion on spill slopes (see Article 3.6.4.2). Rigid revetments have been more successful where abutments are on the floodplain rather than in stream channels because hydrostatic pressure behind the revetments is not usually a problem. Precautions against undermining of the toe and upstream terminus of all revetments are always required (see Article 3.6.4.5). Other countermeasures have been successfully used to inhibit scour at abutments where the abutment is located at the streambank or within the stream channel. These measures include dikes to constrict the width of braided streams and retards to reduce velocities near the streambank. Piers Three basic methods may be used to prevent damage from local scour at piers. The first method is to place the foundation of the structure at such a depth that the structural stability will not be at risk with maximum scour. The second is to provide protection at or below the streambed to inhibit the development of a scour hole. The third measure is to prevent erosive vortices from forming or to reduce their strength and intensity. Streamlining the pier nose decreases flow separation at the face of the pier, reducing the strength of the horseshoe vortices which form at piers. Practical application of this principle involves the use of rounded or circular shapes at the upstream and downstream faces of piers in order to reduce the flow separation. However, flow direction can and does change with time and with stage on some streams. Piers oriented with flow direction at one stage or at one point in time may be skewed with flow direction at another. Also, flow direction changes with the passage of bed forms. In general, piers should be aligned with the main channel design flow © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-75 3 4 Roadway and Ballast direction and skew angles greater than 5 degrees should be avoided. Where this is not possible, a single cylindrical pier or a row of cylindrical columns will produce a lesser depth of local scour. The tendency of a row of columns to collect debris should be considered. Debris can greatly increase scour depths. Webwalls have been used between columns to add to structural strength and to reduce the tendency to collect debris. Webwalls should be constructed at the elevation of stream flood stages which carry floating debris and extended to the elevation of the streambed. When installing a webwall as a countermeasure against debris, the potential for significantly increased scour depths should be considered if the approach flow might impinge on the wall at a high angle of attack. Riprap is commonly used to inhibit local scour at piers at existing bridges. This practice is not recommended as an adequate substitute for foundations or piling located below expected scour depths for new or replacement bridges. It is recommended as a retrofit or a measure to reduce the risk where scour threatens the integrity of a pier (see Article 3.6.4.1). The practice of heaping stones around a pier is not recommended because experience has shown that continual replacement is usually required. Success rates have been better with alluvial bed materials where the top of the riprap was placed at or below the elevation of the streambed. 3.6.3.13 References for Section 3.6.3 Bertoldi, D.A., Jones, J.S., Stein, S.M., Kilgore, R.T., and Atayee, A.T., 1996. "An Experimental Study of Scour Protection Alternatives at Bridge Piers, FHWA-RD-95-187, Office of Engineering and Highway Operations R&D, McLean, VA. Bradley, J.N., 1978. "Hydraulics of Bridge Waterways," Hydraulic Design Series No. 1, U.S. Department of Transportation, FHWA, Washington, D.C. Brice, J.C. and Blodgett, J.C., 1978. "Countermeasure for Hydraulic Problems at Bridges, Volumes 1 and 2," FHWA-RD-78-162 and 163, USGS, Menlo Park, CA. Brown, S.A., 1985. "Design of Spur-type Streambank Stabilization Structures," FHWA/RD-84/101, FHWA, Washington, D.C. Brown, S.A., 1985. "Streambank Stabilization Measures for Highway Engineers, FHWA/RD-84/100, FHWA, Washington, D.C. Brown, S.A. and Clyde, E.S., 1989. "Design of Riprap Revetment," Hydraulic Engineering Circular No. 11, FHWA-IP-89-016, Washington, D.C. Chang, F. and Karim, M., 1972. "An Experimental Study of Reducing Scour Around Bridge Piers Using Piles," South Dakota Department of Highways, Report. Clopper, P.E., 1989. "Hydraulic Stability of Articulated Concrete Block Revetment Systems During Overtopping Flow," FHWA-RD-89-199, Office of Engineering and Highway Operations R&D, McLean, VA. Clopper, P.E., 1992. "Protecting Embankment Dams with Concrete Block Systems," Hydro Review, Vol. X, No. 2, April. Clopper, P.E. and Chen, Y., 1988. "Minimizing Embankment Damage During Overtopping Flow," FHWA-RD-88181, Office of Engineering and Highway Operations R&D, McLean, VA. Federal Highway Administration, 1998. "Scour Monitoring and Instrumentation," Demonstration Project 97 Participants Workbook, FHWA-SA-96-036, Office of Technology Applications, Washington, D.C. Fotherby, L.M. and Ruff, J.F., 1995. "Bridge Scour Protection System Using Toskanes - Phase 1," Pennsylvania Department of Transportation, Report 91-02. Karim, M., 1975. "Concrete Fabric Mat, Highway Focus, Vol. 7. Keown, M.P., 1983. "Streambank Protection Guidelines for Landowners and Local Governments," U.S. Army Corps of Engineers, Waterways Experiment Station, Vicksburg, MS. Lagasse, P.F., Richardson, E.V., Schall, J.D., and Price, G.R., 1997. "Instrumentation for Measuring Scour at Bridge Piers and Abutments," NCHRP Report 396, Transportation Research Board, National Research Council, National Academy Press, Washington, D.C. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-76 AREMA Manual for Railway Engineering Natural Waterways Lagasse, P.F., Schall, J.D., and Richardson, E.V., 2001, "Stream Stability at Highway Structures," Third Edition, Hydraulic Engineering Circular No. 20, FHWA-NHI-01-002, Washington, D.C. Lagasse, P.F., Zevenbergen, L.W., Schall, J.D., and Clopper, P.E., 2001. "Bridge Scour and Stream Instability Countermeasures – Experience, Selection, and Design Guidelines," Second Edition, Report FHWA NHI 01-003, Federal Highway Administration, Hydraulic Engineering Circular No. 23, U.S. Department of Transportation, Washington, D.C. McCorquodale, J.A., 1991. "Guide for the Design and Placement of Cable Concrete Mats," Report Prepared for the Manufacturers of Cable Concrete. McCorquodale, J.A., 1991. "Cable-tied Concrete Block Erosion Protection," Hydraulic Engineering '93, San Francisco, CA, Proceedings (1993), pp. 1367-1372. Odgaard, A.J. and Wang, Y. 1991. "Sediment Management with Submerged Vanes, I and II," Journal of Hydraulic Engineering, ASCE Vol. 117, 3, Washington, D.C. Paice, C. and Hey, R., 1993. "The Control and Monitoring of Local Scour at Bridge Piers," Proceedings Hydraulic Engineering 1993, San Francisco, CA. Richardson, E.V., Simons, D.B., and Lagasse, P.F., 2001. "River Engineering for Highway Encroachments Highways in the River Environment," Report FHWA NHI 01-004, Federal Highway Administration, Hydraulic Design Series No. 6, Washington, D.C. Simons, D.B. and Chen, Y.H., 1984. "Hydraulic Tests to Develop Design Criteria for the Use of Reno Mattresses," Civil Engineering Department - Engineering Research Center, Colorado State University, Fort Collins, CO. U.S. Army Corps of Engineers, 1981. "The Streambank Erosion Control Evaluation and Demonstration Act of 1974," Final Report to Congress, Executive Summary and Conclusions. 1 3.6.4 COUNTERMEASURE DESIGN GUIDANCE (2005) 3.6.4.1 Rock Riprap at Piers and Abutments Introduction 3 Present knowledge for designing riprap at bridge piers is based on research conducted under laboratory conditions with little field verification. Flow turbulence and velocities around a pier are of sufficient magnitude that large rocks move over time. Bridges have been lost due to the removal of riprap at piers resulting from turbulence and high velocity flow. Usually this does not happen during one storm, but is the result of the cumulative effect of a sequence of high flows. Therefore, if rock riprap is placed as scour protection around a pier, the bridge should be monitored and inspected during and after each high flow . event to insure that the riprap is stable Sizing Rock Riprap at Piers As a countermeasure for scour at piers for existing bridges, riprap can reduce the risk of failure. Riprap is not recommended as a pier scour countermeasure for new bridges. Determine the D50 size of the riprap using the rearranged Isbash equation to solve for stone diameter (in meters (ft), for fresh water): 2 0.692 KV D 50 = ------------------------------- S s – 1 2g EQ 23 where: D50 = median stone diameter, m (ft) K = coefficient for pier shape V = velocity on pier, m/s (ft/s) Ss = specific gravity of riprap (normally 2.65) g = 9.81 m/s2 (32.2 ft/s2) © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-77 4 Roadway and Ballast K = 1.5 for round-nose pier K = 1.7 for rectangular pier The effect of turbulence intensity on required rock size is illustrated in Figure 1-3-29. To determine V multiply the average channel velocity (Q/A) by a coefficient that ranges from 0.9 for a pier near the bank in a straight uniform reach of the stream to 1.7 for a pier in the main current of flow around a sharp bend. (1) Provide a riprap mat width which extends horizontally at least two times the pier width, measured from the pier face. (2) Place the top of a riprap mat at the same elevation as the streambed. Placing the bottom of a riprap mat on top of the streambed is discouraged. In all cases where riprap is used for scour control, the bridge must be monitored during and inspected after high flows. It is important to note that it is a disadvantage to bury riprap so that the top of the mat is below the streambed because inspectors have difficulty determining if some or all of the riprap has been removed. Therefore, it is recommended to place the top of a riprap mat at the same elevation as the streambed. (a) The thickness of the riprap mat should be three stone diameters (D50) or more. In general, the bottom of the riprap blanket should be placed at or below the computed contraction scour depth. (b) In some conditions, place the riprap on a geotextile or a gravel filter. However, if a well-graded riprap is used, a filter may not be needed. In some flow conditions it may not be possible to place a filter or if the riprap is buried in the bed a filter may not be needed. (c) The maximum size rock should be no greater than twice the D50 size. Design Example for Riprap at Existing Bridge Piers Riprap is to be sized for an existing 6 ft diameter circular pier. The velocity was determined to be 6 ft/s using the continuity equation. The pier is located between the bank and the thalweg on a gradual bend. A velocity multiplier of 1.2 should be used to account for pier location in the channel, since the calculated value represents a cross section average. The computed contraction scour at the pier is approximately 3.9 ft. Step 1. Determine D50 and Dmax for the riprap protection using EQ 23. 2 0.692 KV D 50 = ------------------------------- S s – 1 2g 2 1.5 1.2 6 D 50 = 0.692 --------------------------------------------------- = 0.8ft 2.65 – 1 2 32.2 D max 2 (0.8) 16 . ft Step 2. Extent of riprap from edge of pier = 2(6) = 12 ft. Step 3. Depth of riprap from streambed at pier = Contraction Scour = 3.9 ft. Step 4. Use well graded riprap such that placement of filter material under water can be avoided. The gradation should be determined using the guidance for revetments (Article 3.6.4.5). This part of the design is not conducted here. Figure 1-3-30 presents the riprap placement resulting from the design. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-78 AREMA Manual for Railway Engineering Natural Waterways (SI Units) 1 3 4 (English Units) Figure 1-3-29. Effect of Turbulence Intensity on Rock Size Using the Isbash Approach © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-79 Roadway and Ballast Figure 1-3-30. Placement of Pier Riprap References for Riprap at Piers Lagasse, P.F., Zevenbergen, L.W., Schall, J.D., and Clopper, P.E., 2001. "Bridge Scour and Stream Instability Countermeasures – Experience, Selection, and Design Guidelines," Second Edition, Report FHWA NHI 01-003, Federal Highway Administration, Hydraulic Engineering Circular No. 23, U.S. Department of Transportation, Washington, D.C. Richardson, E.V. and Davis, S.R., 2001. "Evaluating Scour at Bridges," Hydraulic Engineering Circular 18, Fourth Edition, FHWA NHI 01-001, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C. 3.6.4.2 Rock Riprap at Abutments Introduction The FHWA conducted two research studies in a hydraulic flume to determine equations for sizing rock riprap for protecting abutments from scour (Pagan 1991, Atayee 1993). The first study investigated vertical wall and spill-through abutments which encroached 28 and 56 percent on the floodplain, respectively. The second study investigated spill-through abutments which encroached on a floodplain with an adjacent main channel (Figure 1-3-31). Encroachment varied from the largest encroachment used in the first study to a full encroachment to the edge of main channel bank. For spill-through abutments in both studies, the rock riprap consistently failed at the toe downstream of the abutment centerline (Figure 1-3-32). For vertical wall abutments, the first study consistently indicated failure of the rock riprap at the toe upstream of the centerline of the abutment. Field observations and laboratory studies indicate that with large overbank flow or large drawdown through a bridge opening that scour holes develop on the side slopes of spill-through abutments and the scour can be at the upstream corner of the abutment. In addition, flow separation can occur at the downstream side of a bridge (either with vertical wall or spill-through abutments). This flow separation causes vertical vortices which erode the approach embankment and the downstream corner of the abutment. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-80 AREMA Manual for Railway Engineering Natural Waterways Sizing Rock Riprap at Abutments For Froude Numbers (V/(gy)1/2) 0.80, the recommended design equation for sizing rock riprap for spillthrough and vertical wall abutments is in the form of the Isbash relationship: 2 D 50 K V --------- = -------------------- ------y S s – 1 gy EQ 24 where: D50 = median stone diameter, m (ft) V = characteristics average velocity in the contracted section (explained below), m/s (ft/s) Ss = specific gravity of rock riprap g = gravitational acceleration, 9.81 m/s2 (32.2 ft/s2) y = depth of flow in the contracted bridge opening, m (ft) K = 0.89 for a spill-through abutment 1.02 for a vertical wall abutment For Froude Numbers >0.80, EQ 25 is recommended: 2 D 50 K V ---------- = -------------------- ------y S s – 1 gy 0.14 EQ 25 1 where: K = 0.61 for spill through abutments = 0.69 for vertical wall abutments 3 4 Figure 1-3-31. Section View of a Typical Setup of Spill-through Abutment on a Floodplain With Adjacent Main Channel © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-81 Roadway and Ballast Figure 1-3-32. Plan View of the Location of Initial Failure Zone of Rock Riprap for Spill-through Abutment In both equations, the coefficient K, is a velocity multiplier to account for the apparent local acceleration of flow at the point of rock riprap failure. Both of these equations are envelope relationships that were forced to over predict 90 percent of the laboratory data. A recommended procedure for selecting the characteristic average velocity is as follows: (1) Determine the set-back ratio (SBR) of each abutment. SBR is the ratio of the set-back length to channel flow depth. The set-back length is the distance from the near edge of the main channel to the toe of abutment. SBR = Set-back length/average channel flow depth (a) If SBR is less than 5 for both abutments (Figure 1-3-33), compute a characteristic average velocity, Q/A, based on the entire contracted area through the bridge opening. This includes the total upstream flow, exclusive of that which overtops the railroad. (b) If SBR is greater than 5 for an abutment (Figure 1-3-34), compute a characteristic average velocity, Q/A, for the respective overbank flow only. Assume that the entire respective overbank flow stays in the overbank section through the bridge opening. (c) If SBR for an abutment is less than 5 and SBR for the other abutment at the same site is more than 5 (Figure 1-3-35), a characteristic average velocity determined from Step 1a for the abutment with SBR less than 5 may be unrealistically low. This would, of course, depend upon the opposite overbank discharge as well as how far the other abutment is set back. For this case, the characteristic average velocity for the abutment with SBR less than 5 should be based on the © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-82 AREMA Manual for Railway Engineering Natural Waterways flow area limited by the boundary of that abutment and an imaginary wall located on the opposite channel bank. The appropriate discharge is bounded by this imaginary wall and the outer edge of the floodplain associated with that abutment. (2) Compute rock riprap size from EQ 24 or EQ 25, based on the Froude Number limitation for these equations. (3) Determine extent of rock riprap. (a) The apron at the toe of the abutment should extend along the entire length of the abutment toe, around the curved portions of the abutment to the point of tangency with the plane of the embankment slopes. (b) The apron should extend from the toe of the abutment into the bridge waterway a distance equal to twice the flow depth in the overbank area near the embankment, but need not exceed 25 ft (Figure 1-3-36). (c) Spill-through abutment slopes should be protected with the rock riprap size computed from EQ 24 or EQ 25 to an elevation 2 ft above expected high water elevation for the design flood. Upstream and downstream coverage should agree with step 3a except that the downstream riprap should extend back from the abutment 2 flow depths or 25 ft which ever is larger to protect the approach embankment. In the southeast a guide bank 50 ft long at the downstream end of the abutment to protect the downstream side of the abutment is often used. (d) The rock riprap thickness should not be less than the larger of either 1.5 times D50 or D100. The rock riprap thickness should be increased by 50 percent when it is placed under water to provide for the uncertainties associated with this type of placement. 1 (e) The rock riprap gradation and potential need for underlying filter material must be considered (see Article 3.6.4.5). 3 Design Example for Riprap at Bridge Abutments Riprap is to be sized for an abutment located on the floodplain at an existing bridge. The bridge is 650 ft long, has spill through abutments on a 1V:2H side slope and 7 equally spaced spans. The left abutment is set back from the main channel 225 ft. Given the following table of hydraulic characteristics for the left abutment size the riprap. Hydraulic Property Value Remarks y (ft) 2.7 Flow depth adjacent to abutment Q (cfs) 7,720 Discharge in left overbank A (ft2) 613.5 Flow area of left overbank Step 1. Determine characteristic average velocity, V. Abutment is set back more than 5 average flow depths, therefore overbank discharge and areas are used to determine V. V = Q/A = 7720/613.5 = 12.6 ft/s © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-83 4 Roadway and Ballast Figure 1-3-33. Characteristic Average Velocity for SBR<5 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-84 AREMA Manual for Railway Engineering Natural Waterways 1 3 4 Figure 1-3-34. Characteristic Average Velocity for SBR>5 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-85 Roadway and Ballast Figure 1-3-35. Characteristic Average Velocity for SBR>5 and SBR<5 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-86 AREMA Manual for Railway Engineering Natural Waterways 1 3 4 Figure 1-3-36. Plan View of the Extension of Rock Riprap Apron © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-87 Roadway and Ballast Step 2. Determine the Froude Number of the flow. Fr = V/(gy)1/2 = 12.6/(32.2(2.7)) = 1.35 Step 3. Determine the D50 of the riprap for the left abutment. The Froude Number is greater than 0.8, therefore, use Equation 8.3. 2 D 50 K V ---------- = -------------------- ------y S s – 1 gy 0.14 2 D 50 0.61 12.6 ---------- = --------------------- -----------------------------2.7 2.65 – 1 32.2 2.7 0.14 = 0.40 Step 4. Determine riprap extent and layout. • Extent into floodplain from toe of slope = 2(2.7) = 5.4 ft • Vertical extent up abutment slope from floodplain = 2.0 ft + 2.7 ft = 4.7 ft • The downstream face of the embankment should be protected a distance of 25 ft from the point of tangency between the curved portion of the abutment and the plane of the embankment slope. • Riprap mattress thickness = 1.5 (1.1) = 1.7 ft. Also, the thickness should not be less than D100. • Riprap gradation and filter requirements should be designed using Article 3.6.4.5. This portion of the design is not conducted for this example. References for Riprap at Abutments Atayee, A. Tamin, 1993, "Study of Riprap as Scour Protection for Spill-through Abutment," presented at the 72nd Annual TRB meeting in Washington, D.C., January. Lagasse, P.F., Zevenbergen, L.W., Schall, J.D., and Clopper, P.E., 2001. "Bridge Scour and Stream Instability Countermeasures – Experience, Selection, and Design Guidelines," Second Edition, Report FHWA NHI 01-003, Federal Highway Administration, Hydraulic Engineering Circular No. 23, U.S. Department of Transportation, Washington, D.C. Pagan-Ortiz, Jorge E., 1991, "Stability of Rock Riprap for Protection at the Toe of Abutments Located at the Floodplain," FHWA Research Report No. FHWA-RD-91-057, U.S. Department of Transportation, Washington, D.C. 3.6.4.3 Guide Banks Background When embankments encroach on wide flood plains, the flows from these areas must flow parallel to the approach embankment to the bridge opening. These flows can erode the approach embankment. A severe flow © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-88 AREMA Manual for Railway Engineering Natural Waterways contraction at the abutment can reduce the effective bridge opening, which could possibly increase the severity of abutment and pier scour. Guide banks (formerly known as spur dikes) can be used in these cases to prevent erosion of the approach embankments by cutting off the flow adjacent to the embankment, guiding streamflow through a bridge opening, and transferring scour away from abutments to prevent damage caused by abutment scour. The two major enhancements guide banks bring to bridge design are (1) reduce the separation of flow at the upstream abutment face and thereby maximize the use of the total bridge waterway area, and (2) reduce the abutment scour due to lessening turbulence at the abutment face. Guide banks can be used on both sand- and gravel-bed streams. Principal factors to be considered when designing guide banks, are their orientation to the bridge opening, plan shape, upstream and downstream length, cross-sectional shape, and crest elevation. Bradley is used as the principal design reference for this section (Bradley 1978). Figure 1-3-37 presents a typical guide bank plan view. It is apparent from the figure that without this guide bank overbank flows would return to the channel at the bridge opening, which can increase the severity of contraction and scour at the abutment. Note, that with installation of guide banks the scour holes which normally would occur at the abutments of the bridge are moved upstream away from the abutments. Guide banks may be designed at each abutment, as shown, or singly, depending on the amount of overbank or flood plain flow directed to the bridge by each approach embankment. 1 3 4 Figure 1-3-37. Typical Guide Bank (Modified from Bradley) The goal in the design of guide banks is to provide a smooth transition and contraction of the streamflow through the bridge opening. Ideally, the flow lines through the bridge opening should be straight and parallel. As in the case with other countermeasures, the designer should consider the principles of river hydraulics and morphology, and exercise sound engineering judgment. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-89 Roadway and Ballast Design Guidelines Orientation: Guide banks should start at and be set parallel to the abutment and extend upstream from the bridge opening. If there are guide banks at each abutment, the distance between them at the bridge opening should be equal to the distance between bridge abutments. Best results are obtained by using guide banks with a plan form shape in the form of a quarter of an ellipse, with the ratio of the major axis (length Ls) to the minor axis (offset) of IV:2.5H. This allows for a gradual constriction of the flow. Thus, if the length of the guide bank measured perpendicularly from the approach embankment to the upstream nose of the guide bank is denoted as Ls, the amount of expansion of each guide bank (offset), measured from the abutment parallel to the approach embankment, should be 0.4 Ls. The plan view orientation can be determined using EQ 26, which is the equation of an ellipse with origin at the base of the guide bank. For this equation, X is the distance measured perpendicularly from the bridge approach and Y is the offset measured parallel to the approach embankment, as shown on Figure 1-3-37. EQ 26 It is important that the face of the guide bank match the abutment so that the flow is not disturbed where the guide bank meets the abutment. For new bridge construction, abutments can be sloped to the channel bed at the same angle as the guide bank. For retrofitting existing bridges modification of the abutments or wing walls may be necessary. Length: For design of guide banks, the length of the guide bank, Ls must first be determined. This can be easily determined using a nomograph which was developed from laboratory tests performed at Colorado State University and from field data compiled by the USGS. For design purposes the use of the nomograph involves the following parameters: Q = total discharge of the stream, m3/s (ft3/s) Qf = lateral or flood plain discharge of either flood plain intercepted by the embankment, m3/s (cfs) (ft3/s) QA = discharge in 30 m (100 ft) of stream adjacent to the abutment, m3/s (ft3/s) b = length of the bridge opening, m (ft) An2 = cross-sectional flow area at the bridge opening at normal stage, m2 (ft2) Vn2 = Q/An2 = average velocity through the bridge opening, m/s (ft/s) Qf/QA = guide bank discharge ratio Ls = projected length of guide bank, m (ft) A nomograph is presented in Figure 1-3-38 to determine the projected length of guide banks. This nomograph should be used to determine the guide bank length for designs greater than 50 ft and less than 250 ft. If the nomograph indicates the length required to be greater than 250 ft the design should be set at 250 ft. It is recommended that the minimum length of guide banks be 50 ft. An example of how to use this nomograph is presented in the next section. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-90 AREMA Manual for Railway Engineering Natural Waterways 1 3 4 Figure 1-3-38. English Version of Nomograph to Determine Guidebank Length (after Bradley) FHWA practice has shown that many guide banks have performed well using a standardized length of 150 ft. Based on this experience, guide banks of 150 ft in length should perform very well in most locations. Even shorter guide banks have been successful if the guide bank intersects the tree line. If the main channel is equal to or less than 100 ft use the total main channel flow in determining the guide bank discharge ratio (Qf/QA). Crest Height: As with deflection spurs, guide banks should be designed so that they will not be overtopped at the design discharge. If this were allowed to occur, unpredictable cross flows and eddies might be generated, which could scour and undermine abutments and piers. In general, a minimum of 2 ft of freeboard, above the design water surface elevation should be maintained. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-91 Roadway and Ballast Shape and Size: The cross-sectional shape and size of guide banks should be similar to deflector, or deflector/retarder spurs discussed in Article 3.6.4.4. Generally, the top width is 10 to 13 ft, but the minimum width is 3 ft when construction is by drag line. The upstream end of the guide bank should be round nosed. Side slopes should be 1V:2H or less. Downstream Extent: In some locations, guide banks have been extended downstream of the abutments to minimize scour due to rapid expansion of the flow at the downstream end of the abutments. These downstream guide banks are sometimes called "heels." If the expansion of the flow is too abrupt, a shorter guide bank, which usually is less than 50 ft long, can be used downstream. Downstream guide banks should also start at and start parallel to the abutment and the distance between them should enlarge as the distance from the abutment of the bridge increases. In general, downstream guide banks are a shorter version of the upstream guide banks. Riprap protection, crest height and width should be designed in the same manner as for upstream guide banks. Riprap: Guide banks are constructed by forming an embankment of soil or sand extending upstream from the abutment of the bridge. To inhibit erosion of the embankment materials, guide banks must be adequately protected with riprap or stone facing. Rock riprap should be placed on the stream side face as well as around the end of the guide bank. It is not necessary to riprap the side of the guide bank adjacent to the railroad approach embankment. As in the case of spurs, a gravel, sand, or geotextile filter may be required to protect the underlying embankment material (see HEC-11 and Article 3.6.4.5). Riprap should be extended below the bed elevation to a depth as recommended in Article 3.6.4.5 (below the combined long-term degradation and contraction scour depth), and extend up the face of the guide bank to 2 ft above the design flow. Additional riprap should be placed around the upstream end of the guide bank so to protect the embankment from scour. As in the case of spurs, it is important to adequately tie guide banks into the approach embankment for guide banks on non-symmetrical railroad crossings. Hydraulics of Bridge Waterways (Bradley 1978) states: "From meager testing done to date, there is not sufficient evidence to warrant using longer dikes (guide banks) at either abutment on skewed bridges. Lengths obtained from [the nomograph] should be adequate for either normal or skewed crossings." Therefore, for skewed crossings, the length of guide banks should be set using the nomograph for the side of the bridge crossing which yields the largest guide bank length. Other Design Concerns: In some cases, where the cost of stone riprap facing is prohibitive, the guide bank can be covered with sod or other minimal protection. If this approach is selected, the design should allow for and stipulate the repair or replacement of the guide bank after each high water occurrence. Other measures which will minimize damage to approach embankments, and guide banks during high water are: Keep trees as close to the toe of guide bank embankments as construction will permit. Trees will increase the resistance to flow near and around the toe of the embankment, thus reducing velocities and scour potential. Do not allow the cutting of channels or the digging of borrow pits along the upstream side of approach embankments and near guide banks. Such practices encourage flow concentration and increases velocities and erosion rates of the embankments. In some cases, the area behind the guide bank may be too low to drain properly after a period of flooding. This can be a problem, especially when the guide bank is relatively impervious. Small drain pipes can be installed in the guide bank to drain this ponded water. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-92 AREMA Manual for Railway Engineering Natural Waterways In some cases, only one approach will cut off the overbank flow. This is common when one of the banks is high and well defined. In these cases, only one guide bank may be necessary. Design Example Of Guide Bank Installation For the example design of a guide bank, Figure 1-3-39 will be used. This figure shows the cross-section of the channel and flood plain before the bridge is constructed and the plan view of the approach, guide banks, and embankments after the design steps outlined below are completed. Step 1. Hydraulic Design Parameters The first step in the design of guide banks requires the computation of the depth and velocity of the design flood in the main channel and in the adjacent overbank areas. These studies are performed by using step backwater computations upstream and through the bridge opening. The computer program HEC River Analysis System (RAS) is suitable for these computations. Using this program or by using conveyance curves developed from actual data, the discharges and depths in the channel and overbank areas can be determined. To use the conveyance curve approach, the designer is referred to example problem number 4 in Hydraulics of Bridge Waterways (Bradley 1978) for methods to determine these discharges and areas. That publication also contains another example of the design of a guide bank. For this example, the total, overbank, and channel discharges, as well as the flow area are given. We also assume that a bridge will span a channel with a bottom width of 230 ft and that the abutments will be set back 148 ft from each bank of the main channel. The abutments of this bridge are spill-through with a side slope of 1V:2H. The design discharge is 12,360 cfs, which after backwater computations, results in a mean depth of 11.8 ft in the main channel and a mean channel velocity of 3 ft/s. Step 2. Determine Qf in the Left and Right Overbank 1 3 The depth in each overbank area is given as 3.9 ft and the widths of the left and right overbank areas are 295 ft and 590 ft, respectively. Velocity in the overbank areas (assuming no railroad approach embankment, i.e., at an upstream cross section) is 1.2 ft/s. The floodplain flow is equal to 1,413 cfs for the left overbank and 2,825 cfs for the right overbank. 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-93 Roadway and Ballast Figure 1-3-39. Example Guide Bank Design Using the continuity equation and noting that the abutments are set back 148 ft from each bank, the flood plain discharge intercepted by each approach embankment is: Q = AV (Qf) right = 2,825 - (148) (3.9) (1.2) = 2132 cfs (Qf) left = 1,413 - (148 (3.9) (1.2) = 720 cfs Step 3. Determine QA and Qf/QA for the Left and Right Overbank The overbank discharge in the first 100 ft of opening adjacent to the left and right abutments needs to be determined next. Since for this case the flow is of uniform depth (3.9 ft) and velocity (1.2 ft/s) over the entire width of the floodplain, and both abutments are set back more than 100 ft from the main channel banks, the value of QA will be the same for both sides: (QA) right = (100) (3.9) (1.2) = 468 cfs (QA) left = (100 (3.9) (1.2) = 468 cfs © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-94 AREMA Manual for Railway Engineering Natural Waterways For the left and right overbanks the reference values of Qf /QA can be determined by simple division of the discharges determined in previous steps: For design purposes, the largest value will result in the more conservative determination of the length of the guide banks, except where Step 4 indicates a guide bank is required for only one of the overbank areas. Step 4. Determine the Length of the Guide Bank, Ls The average channel velocity through the bridge opening can be determined by dividing the total discharge of the stream, Q, by the cross-sectional flow area at the bridge opening, An2, which in this case includes the main channel (2,714 ft2) plus 148 ft of the left and right overbank areas adjacent to the abutments at the bridge opening (1,154 ft2). Thus: 1 For Qf /QA equal to 4.5 and an average channel velocity of 3.2 ft/s, the length of the guide bank is determined using the nomograph presented in Figure 1-3-38. For the left abutment, a Qf /QA of 1.5 and Vn2 of 3.2 ft/s indicate that Ls would be less than 50 ft. Thus, no guide bank is required for the left overbank for this example. 3 Step 5. Miscellaneous Specifications The offset of the guidebank is determined to be 55.2 ft by multiplying Ls by 0.4. The offset and length determine the plan layout of the guide bank. Coordinates of points along the centerline can be determined using EQ 26, which is the equation of an ellipse with a major to minor axis ratio of 2.5:1. The coordinates for a 138 ft long guide bank with a 55.2 ft offset are presented in Table 1-3-15. These coordinates would be used for conceptual level design. For construction, coordinates at an offset or along the toe of side slope would be necessary. The crest of the guide bank must be a minimum of 2 ft above the design water surface (elevation 1070.2 ft). Therefore, the crest elevation for this example should be greater than or equal to 1072.2 ft. The crest width should be at least 3 ft. For this example, a crest width of 10 ft will be specified so that the guide bank can be easily constructed with dump trucks. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-95 4 Roadway and Ballast Table 1-3-15. Coordinates for Guide Bank on the Right Bank of Figure 10.4 X (ft) Y (ft) 0 55.2 30 53.9 60 49.7 90 41.8 120 27.3 138 0.0 Stone or rock riprap should be placed in the locations shown on Figure 1-3-39. This riprap should extend a minimum of 2 ft above the design water surface (elevation 1070.2 m) and below the intersection of the toe of the guide bank and the existing ground to the combined long-term degradation and contraction scour depth. References for Guidebank Design Bradley, J.N., 1978. "Hydraulics of Bridge Waterways," Hydraulic Design Series No. I U.S. Department of Transportation, FHWA. Brown, S.A. and Clyde, E.S., 1989. "Design of Riprap Revetment," Hydraulic Engineering Circular No. 11, FHWA-IP-89-016. Prepared for the Federal Highway Administration, Washington, D.C. Karaki, S.S., 1959. "Hydraulic Model Study of Spur Dikes for Highway Bridge Openings," Colorado State University, Civil Engineering Section, Report CER59SSK36, September, 47 pp. Karaki, S.S., 1961. "Laboratory Study of Spur Dikes for Highway Bridge Protection," Highway Research Board Bulletin 286, Washington, D.C., p. 31. Lagasse, P.F., Zevenbergen, L.W., Schall, J.D., and Clopper, P.E., 2001. "Bridge Scour and Stream Instability Countermeasures – Experience, Selection, and Design Guidelines," Second Edition, Report FHWA NHI 01-003, Federal Highway Administration, Hydraulic Engineering Circular No. 23, U.S. Department of Transportation, Washington, D.C. U.S. Army Corps of Engineers, 2001. "HEC-RAS River Analysis System," User's Manual, Version 3.0 , Hydrologic Engineering Center, Davis, CA. 3.6.4.4 Spurs Background A spur can be a pervious or impervious structure projecting from the streambank into the channel. Spurs are used to deflect flowing water away from, or to reduce flow velocities in critical zones near the streambank, to prevent erosion of the bank, and to establish a more desirable channel alignment or width. The main function of spurs is to reduce flow velocities near the bank, which in turn, encourages sediment deposition due to these reduced velocities. Increased protection of banks can be achieved over time, as more sediment is deposited behind the spurs. Because of this, spurs may protect a streambank more effectively and at less cost than revetments. Furthermore, by moving the location of any scour away from the bank, partial failure of the spur can often be repaired before damage is done to structures along and across the stream. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-96 AREMA Manual for Railway Engineering Natural Waterways Spurs are generally used to halt meander migration at a bend. They are also used to channelize wide, poorly defined streams into well-defined channels. The use of spurs to establish and maintain a well-defined channel location, cross section, and alignment in braided streams can decrease the required bridge lengths, thus decreasing the cost of bridge construction and maintenance. Spur types are classified based upon their permeability as retarder spurs, retarder/deflector spurs, and deflector spurs. The permeability of spurs is defined simply as the percentage of the spur surface area facing the streamflow that is open. Deflector spurs are impermeable spurs which function by diverting the primary flow currents away from the bank. Retarder/deflector spurs are more permeable and function by retarding flow velocities at the bank and diverting flow away from the bank. Retarder spurs are highly permeable and function by retarding flow velocities near the bank. Design Considerations Spur design includes setting the limits of bank protection required; selection of the spur type to be used; and design of the spur installation including spur length, orientation, permeability, height, profile, and spacing. Longitudinal Extent of Spur Field. The longitudinal extent of channel bank requiring protection is discussed in Brown (1985, 1989). Figure 1-3-40 was developed from USACE studies of the extent of protection required at meander bends (USACE 1981). The minimum extent of bank protection determined from Figure 1-3-40 should be adjusted according to field inspections to determine the limits of active scour, channel surveys at low flow, and aerial photography and field investigations at high flow. Investigators of field installations of bank protection have found that protection commonly extends farther upstream than necessary and not far enough downstream. However, such protection may have been necessary at the time of installation. The lack of a sufficient length of protection downstream is generally more serious, and the downstream movement of meander bends should be considered in establishing the downstream extent of protection. 1 3 4 Figure 1-3-40. Extent of Protection Required at a Channel Bend (after USACE) Spur Length. Spur length is taken here as the projected length of spur normal to the main flow direction or from the bank. Where the bank is irregular, spur lengths must be adjusted to provide for an even curvature of the thalweg. The length of both permeable and impermeable spurs relative to channel width affects local scour © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-97 Roadway and Ballast depth at the spur tip and the length of bank protected. Laboratory tests indicate that diminishing returns are realized from spur lengths greater than 20 percent of channel width. The length of bank protected measured in terms of projected spur length is essentially constant up to spur lengths of 20 percent of channel width for permeable and impermeable spurs. Field installations of spurs have been successful with lengths from 3 to 30 percent of channel width. Impermeable spurs are usually installed with lengths of less than 20 percent while permeable spurs have been successful with lengths up to 25 percent of channel width. However, only the most permeable spurs were effective at greater lengths. The above discussion assumes that stabilization of the bend is the only objective when spur lengths are selected. It also assumes that the opposite bank will not erode. Where flow constriction or changing the flow path is also an objective, spur lengths will depend on the degree of constriction required or the length of spur required to achieve the desired change in flow path. At some locations, channel excavation on the inside of the bend may be required where spurs would constrict the flow excessively. However, it may be acceptable to allow the stream to do its own excavation if it is located in uniformly graded sand Spur Orientation. Spur orientation refers to spur alignment with respect to the direction of the main flow current in a channel. Figure 1-3-41 defines the spur angle such that an acute spur angle means that the spur is angled in an downstream direction and an angle greater than 90 indicates that the spur is oriented in a upstream direction. Figure 1-3-41. Definition Sketch for Spur Angle (after Karaki 1959) Permeable retarder spurs are usually designed to provide flow retardance near the streambank, and they perform this function equally as well without respect to the spur angle. Since spurs oriented normal to the bank and projecting a given length into the channel are shorter than those at any other orientation, all retarder spurs should be constructed at 90 with the bank for reasons of economy. Spur orientation at approximately 90 has the effect of forcing the main flow current (thalweg) farther from the concave bank than spurs oriented in an upstream or downstream direction. Therefore, more positive flow control is achieved with spurs oriented approximately normal to the channel bank. Spurs oriented in an upstream direction cause greater scour than if oriented normal to the bank, and spurs oriented in a downstream direction cause less scour. It is recommended that the spur furthest upstream be angled downstream to provide a smoother transition of the flow lines near the bank and to minimize scour at the nose of the leading spur. Subsequent spurs downstream should all be set normal to the bank line to minimize construction costs. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-98 AREMA Manual for Railway Engineering Natural Waterways Spur Permeability. The permeability of the spur depends on stream characteristics, the degree of flow retardance and velocity reduction required, and the severity of the channel bend. Impermeable spurs can be used on sharp bends to divert flow away from the outer bank. Where bends are mild and only small reductions in velocity are necessary, highly permeable retarder spurs can be used successfully. However, highly permeable spurs can also provide required bank protection under more severe conditions where vegetation and debris will reduce the permeability of the spur without destroying the spur. This is acceptable provided the bed load transport is high. Spurs of varying permeability will provide protection against meander migration. Impermeable spurs provide more positive flow control but cause more scour at the toe of the spur and, when submerged, cause erosion of the streambank. High permeability spurs are suitable for use where only small reductions in flow velocities are necessary as on mild bends but can be used for more positive flow control where it can be assumed that clogging with small debris will occur and bed load transport is large. Spurs with permeability up to about 35 percent can be used in severe conditions but permeable spurs may be susceptible to damage from large debris and ice. Spur Height and Crest Profile. Impermeable spurs are generally designed not to exceed the bank height because erosion at the end of the spur in the overbank area could increase the probability of outflanking at high stream stages. Where stream stages are greater than or equal to the bank height, impermeable spurs should be equal to the bank height. If flood stages are lower than the bank height, impermeable spurs should be designed so that overtopping will not occur at the bank. Bank erosion is more severe if the spur is oriented in the downstream direction. The crest of impermeable spurs should slope downward away from the bank line, because it is difficult to construct and maintain a level spur of rock or gabions. Use of a sloping crest will avoid the possibility of overtopping at a low point in the spur profile, which could cause damage by particle erosion or damage to the streambank. 1 Permeable spurs, and in particular those constructed of light wire fence, should be designed to a height that will allow heavy debris to pass over the top. However, highly permeable spurs consisting of jacks or tetrahedrons are dependent on light debris collecting on the spur to make them less permeable. The crest profile of permeable spurs is generally level except where bank height requires the use of a sloping profile. 3 Bed and Bank Contact. The most common causes of spur failure are undermining and outflanking by the stream. These problems occur primarily in alluvial streams that experience wide fluctuations in the channel bed. Impermeable rock riprap spurs and gabion spurs can be designed to counter erosion at the toe by providing excess material on the streambed as illustrated in Figure 1-3-42 and Figure 1-3-43. As scour occurs, excess material is launched into the scour hole, thus protecting the end of the spur. Gabion spurs are not as flexible as riprap spurs and may fail in very dynamic alluvial streams. 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-99 Roadway and Ballast Figure 1-3-42. Launching of Stone Protection on a Riprap Spur (a) before launching at low flow, (b) during launching at high flow, and (c) after scour subsides (after Brown) © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-100 AREMA Manual for Railway Engineering Natural Waterways 1 3 4 Figure 1-3-43. Gabion Spur Illustrating Flexible Mat Tip Protection (a) before launching at low flow, (b) during launching at high flow, and (c) after scour subsides (after Brown) © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-101 Roadway and Ballast Permeable spurs can be similarly protected with a riprap toe as illustrated in Figure 1-3-44. The necessity for using riprap on the full length of the spur or any riprap at all is dependent on the erodibility of the streambed, the distance between the slats and the streambed, and the depth to which the piling are driven. This would also be appropriate as a retrofit measure at a spur that has been severely undermined, and as a design for locations at which severe erosion of the toe of the streambank is occurring. Figure 1-3-44. Permeable Wood-slat Fence Spur Showing Launching of Stone Toe Material (after Brown) Piles supporting permeable structures can also be protected against undermining by driving piling to depths below the estimated scour. Round piling are recommended because they minimize scour at their base. Extending the facing material of permeable spurs below the streambed also significantly reduces scour. If the retarder spur or retarder/deflector spur performs as designed, retardance and diversion of the flow within the length of the structure may make it unnecessary to extend the facing material the full depth of anticipated scour except at the nose. Spur Spacing. Spur spacing is a function of spur length, spur angle, permeability, and the degree of curvature of the bend. The flow expansion angle, or the angle at which flow expands toward the bank downstream of a spur, is a function of spur permeability and the ratio of spur length to channel width. This ratio is susceptible to alteration by excavation on the inside of the bend or by scour caused by the spur installation. Figure 1-3-45 indicates that the expansion angle for impermeable spurs is an almost constant 17. Spurs with 35 percent permeability have almost the same expansion angle except where the spur length is greater than about 18 percent of the channel width. As permeability increases, the expansion angle increases, and as the length of spurs relative to channel width increases, the expansion angle increases exponentially. The expansion angle varies with the spur angle, but not significantly. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-102 AREMA Manual for Railway Engineering Natural Waterways Figure 1-3-45. Relationship Between Spur Length and Expansion Angle for Several Spur Permeabilities (after Brown) 1 Spur spacing in a bend can be established by first drawing an arc representing the desired flow alignment (Figure 1-3-46). This arc will represent the desired extreme location of the thalweg nearest the outside bank in the bend. The desired flow alignment may differ from existing conditions or represent no change in conditions, depending on whether there is a need to arrest erosion of the concave bank or reverse erosion that has already occurred. If the need is to arrest erosion, permeable retarder spurs or retarder structures may be appropriate. If the flow alignment must be altered in order to reverse erosion of the bank or to alter the flow alignment significantly, deflector spurs or retarder/deflector spurs are appropriate. The arc representing the desired flow alignment may be a compound circular curve or any curve which forms a smooth transition in flow directions. 3 4 Figure 1-3-46. Spur Spacing in a Meander Bend (after Brown) © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-103 Roadway and Ballast Next, draw an arc representing the desired bankline. This may approximately describe the existing concave bank or a new theoretical bankline which protects the existing bank from further erosion. Also, draw an arc connecting the nose (tip) of spurs in the installation. The distance from this arc to the arc describing the desired bank line, along with the expansion angle, fixes the spacing between spurs. The arc describing the ends of spurs projecting into the channel will be essentially concentric with the arc describing the desired flow alignment. Establish the location of the spur at the downstream end of the installation. This is normally the protected abutment or guidebank at the bridge. Finally, establish the spacing between each of the remaining spurs in the installation (Figure 1-3-46). The distance between spurs, S, is the length of spur, L, between the arc describing the desired bank line and the nose of the spur multiplied by the cotangent of the flow expansion angle, . This length is the distance between the nose of spurs measured along a chord of the arc describing spur nose location. Remaining spurs in the installation will be at the same spacing if the arcs are concentric. The procedure is illustrated by Figure 1-3-46 and expressed in EQ 27. S = L cot EQ 27 where: S = spacing between spurs at the nose, m (ft) L = effective length of spur, or the distance between arcs describing the toe of spurs and the desired bank line, m (ft) expansion angle downstream of spur nose, degrees At less than bankfull flow rates, flow currents may approach the concave bank at angles greater than those estimated from Figure 1-3-45. Therefore, spurs should be well-anchored into the existing bank, especially the spur at the upstream end of the installation, to prevent outflanking. Shape and Size of Spurs. In general, straight spurs should be used for most bank protection. Straight spurs are more easily installed and maintained and require less material. For permeable spurs, the width depends on the type of permeable spur being used. Less permeable retarder/deflector spurs which consist of a soil or sand embankment should be straight with a round nose as shown in Figure 1-3-47. The top width of embankment spurs should be a minimum of 3 ft. However, in many cases the top width will be dictated by the width of any earth moving equipment used to construct the spur. In general a top width equal to the width of a dump truck can be used. The side slopes of the spur should be 1V:2H or flatter. Riprap. Rock riprap should be placed on the upstream and downstream faces as well as on the nose of the spur to inhibit erosion of the spur. Depending on the embankment material being used, a gravel, sand, or geotextile may be required (see HEC-11). The designer is referred to HEC-11 and Article 3.6.4.5 for design procedures for sizing riprap at spurs. It is recommended that riprap be extended below the bed elevation to a depth equal to the combined long-term degradation and contraction scour depth. Riprap should also extend to the crest of the spur, in cases where the spur would be submerged at design flow, or to 2 ft above the design flow, if the spur crest is higher than the design flow depth. Additional riprap should be placed around the nose of the spur (Figure 1-3-47), so that spur will be protected from scour. Figure 1-3-48 shows an example of an impermeable spur field and a close-up of a typical round nose spur installation. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-104 AREMA Manual for Railway Engineering Natural Waterways Figure 1-3-47. Typical Straight, Round Nose Spur Design Example of Spur Installation Figure 1-3-49 illustrates a location at which a migrating bend threatens an existing bridge (existing conditions are shown with a solid line). Ultimately, based upon the following design example, seven spurs will be required. Although the number of spurs is not known in advance, the spurs (and other design steps) are shown as dashed lines on Figure 1-3-49 as they will be specified after completing the following design example. Assume that the width of the river from the desired (north) bankline to the existing (south) bankline is 164 ft. For this example, it is desirable to establish a different flow alignment and to reverse erosion of the concave (outside) bank. The spur installation has two objectives: (1) to stop migration of the meander before it damages the railroad stream crossing, and (2) to reduce scour at the bridge abutment and piers by aligning flow in the channel with the bridge opening. Impermeable deflector spurs are suitable to accomplish these objectives and the stream regime is favorable for the use of this type of countermeasure. The expansion angle for this spur type is approximately 17 for a spur length of about 20 percent of the desired channel width, as indicated in Figure 1-3-45. 1 3 Step 1. Sketch Desired Thalweg The first step is to sketch the desired thalweg location (flow alignment) with a smooth transition from the upstream flow direction through the curve to an approach straight through the bridge waterway (Figure 1-349). Visualize both the high-flow and low-flow thalwegs. For an actual location, it would be necessary to examine a greater length of stream to establish the most desirable flow alignment. Then draw an arc representing the desired bankline in relation to thalweg locations. The theoretical or desired left bank line is established as a continuation of the bridge abutment and left bank downstream through the curve, smoothly joining the left bank at the upstream extremity of eroded bank. Step 2. Sketch Alignment of Spur Tips The second step is to sketch a smooth curve through the nose (tip) locations of the spurs, concentric with the desired bankline alignment. Using a guideline of 20 percent of the desired channel width for impermeable spurs (see Spur Length) the distance, L, from the desired bankline to the spur tips (Figure 1-3-49) would be: L = 0.20(164ft) = 33ft © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-105 4 Roadway and Ballast Figure 1-3-48. Impermeable Spur Field in Top Photograph With Close-up Shot of One Spur in the Lower Photograph, Vicinity of the Richardson Highway, Delta River, Alaska © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-106 AREMA Manual for Railway Engineering Natural Waterways Figure 1-3-49. Example of Spur Design 1 Step 3. Locate First Spur Step number three is to locate spur number 1 so that flow expansion from the nose of the spur will intersect the streambank downstream of the abutment. This is accomplished by projecting an angle of 17 from the abutment alignment to an intersection with the arc describing the nose of spurs in the installation or by use of EQ 27. Spurs are set at 90 to a tangent with the arc for economy of construction. Alternatively, the first spur could be considered to be either the upstream end of the abutment or guide bank if the spur field is being installed upstream of a bridge. Thus, the spur spacing, S, would be: 3 S = L cot = (33ft) cot17 = 108ft It may be desirable to place riprap on the streambank at the abutment. Furthermore, the size of the scour hole at the spur directly upstream of the bridge should be estimated using the procedures described in Article 3.5.5. If the extent of scour at this spur overlaps local scour at the pier, total scour depth at the pier may be increased. This can be determined by extending the maximum scour depth at the spur tip, up to the existing bed elevation at the pier at the angle of repose. Step 4. Locate Remaining Spurs Spurs upstream of spur number 1 are then located by use of EQ 27, using dimensions as illustrated in Figure 13-46 (i.e., the spacing, S, determined in Step 3). Using this spur spacing, deposition will be encouraged between the desired bank line and the existing eroded bank. The seventh and last spur upstream is shown oriented in a downstream direction to provide a smooth transition of the flow approaching the spur field. This spur could have been oriented normal to the existing bank, and been shorter and more economical, but might have caused excessive local scour. Orienting the furthest upstream spur at an angle in the downstream direction provides a smoother transition into the spur field, and decreases scour at the nose of the spur. As an alternative, a hard point could be installed where the © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-107 4 Roadway and Ballast bank is beginning to erode (see Article 3.6.4.9). In this case the hard point can be considered as a very short spur which is located at the intersection of the actual and planned bank lines. In either case, spurs or hard points should be anchored well into the bank to prevent outflanking. References for Spur Design Brown, S.A., 1985. "Streambank Stabilization Measures for Highway Stream Crossings–Executive Summary," FHWA/RD-84/099, Federal Highway Administration, Washington, D.C. Brown, S.A., 1985. "Streambank Stabilization Measures for Highway Engineers," FHWA/RD-84. 100 Federal Highway Administration, McLean, VA. Brown, S.A. and Clyde, E.S., 1989. "Design of Riprap Revetment," Hydraulic Engineering Circular No.11, FHWA-IP-89-016. Prepared for the Federal Highway Administration, Washington, D.C. Karaki, S.S., 1959. "Hydraulic Model Study of Spur Dikes for Highway Bridge Openings," Colorado State University, Civil Engineering Section, Report CER59SSK36, September, 47 pp. Lagasse, P.F., Zevenbergen, L.W., Schall, J.D., and Clopper, P.E., 2001. "Bridge Scour and Stream Instability Countermeasures – Experience, Selection, and Design Guidelines," Second Edition, Report FHWA NHI 01-003, Federal Highway Administration, Hydraulic Engineering Circular No. 23, U.S. Department of Transportation, Washington, D.C. Richardson, E.V. and Davis, S.R., 2000. "Evaluating Scour at Bridges," Report FHWA NHI 01-001, Federal Highway Administration, Hydraulic Engineering Circular No. 18, U.S. Department of Transportation, Washington, D.C. Richardson, E.V., Simons, D.B., and Lagasse, P.F., 2001. "River Engineering for Highway Encroachments Highways in the River Environment," Report No. FHWA NHI 01-004, Hydraulic Design Series No. 6, Federal Highway Administration, Washington, D.C. U.S. Army Corps of Engineers, 1981. "The Streambank Erosion Control Evaluation and Demonstration Act of 1974," Final Report to Congress, Executive Summary and Conclusions. 3.6.4.5 Revetments Introduction Revetments are used to provide protection for embankments, streambanks, and streambeds. They may be flexible or rigid and can be used to counter all erosion mechanisms. They do not significantly constrict channels or alter flow patterns. Revetments do not provide resistance against slumping in saturated streambanks and embankments, and are relatively unsuccessful in stabilizing streambanks and streambeds in degrading streams. Special precautions must be observed in the design of revetments for degrading channels. Flexible Revetments Flexible revetments include rock riprap, rock-and-wire mattresses, gabions, precast concrete blocks, rock-fill trenches, windrow revetments, used tire revetments, and vegetation. Rock riprap adjusts to distortions and local displacement of materials without complete failure of the revetment installation. However, flexible rock-and-wire mattress and gabions may sometimes span the displacement of underlying materials, but usually can adjust to most local distortions (see Article 3.6.4.6). Used tire mattresses and precast concrete block mattresses are generally stiffer than rock riprap and gabions and, therefore, do not adjust well to local displacement of underlying materials. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-108 AREMA Manual for Railway Engineering Natural Waterways Design guidelines, design procedures, and suggested specifications for rock riprap, wire enclosed rock, stacked block gabions, and precast concrete blocks are included in HEC-11. Since rock riprap is commonly used as a countermeasure for stream bank erosion, a short discussion of the types of rock riprap and a design procedure as discussed in HEC-11 follows. Riprap as discussed in this section is defined as a flexible channel or bank lining consisting of a well-graded mixture of angular rock usually dumped in place. Other types of riprap are "hand-placed" and "keyed or plated" riprap. Hand-placed riprap is carefully placed by hand or by a mechanized manner in a definite pattern with voids between the large stone being filled with smaller rock. Plated riprap is placed on the bank with a skip and tamped into place using a heavy steel plate leaving a smoother surface than dumped riprap. See HEC-11 for more information on each of these types. Dumped riprap does not mean end dumping from trucks and allowing the material to roll down the slope which can cause size segregation. It means that the riprap is placed in a manner to prevent segregation by using a crane with a bucket or dragline. Regardless of how it is placed, care should be taken to prevent segregation of the rock mixture. Dumped riprap should form a layer of loose stone where individual stones may move independently to adjust to the movement of the bank material being protected. This minor movement may occur without complete failure of the installation. This movement allows the riprap to be somewhat "self healing" and is one of the main advantages of dumped rock riprap. Design Guidelines HEC-11 provides design guidance for sizing the rock for dumped riprap used for bank protection. The procedure is based on the tractive force theory but has velocity as its primary design parameter. The equation is based on the assumption of uniform or gradually varying flow. A stability factor is used to correct the equation for bends and turbulent mixing at rapidly varying flow conditions. 1 The stone size is established by this equation: EQ 28 3 where: D50 = median particle size, m (ft) C = correction for specific gravity and stability factor Va = average velocity in the main channel, m/s (fps) davg = average flow depth in the main flow channel, m (ft) K1 = bank angle correction factor as given below Ku = 0.0059 SI Ku = 0.001 English 4 2 0.5 sin K 1 = 1 – -------------2 sin EQ 29 where: bank angle with the horizontal riprap material’s angle of repose as given in Figure 1-3-50 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-109 Roadway and Ballast Figure 1-3-50. Angle of Repose of Riprap in Terms of Mean Size and Shape of Stone (Chen and Cotton 1988) The average flow depth and velocity used in EQ 28 are main channel values where the main channel is defined as the area between the channel banks. The correction for the specific gravity and the stability factor is defined by the following equation: 1.5 1.61 SF C = ------------------------------1.5 Ss – 1 EQ 30 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-110 AREMA Manual for Railway Engineering Natural Waterways where: Ss = specific gravity of the rock riprap SF = stability factor as described below The stability factor (SF) is defined as the ratio of the riprap material critical shear stress and average tractive force exerted by the flow field. As long as the SF is greater than 1, the critical shear stress of the material is greater than the flow induced tractive stress, and the riprap is considered stable. A SF of 1.2 was used in the development of EQ 28. The SF may be used to reflect the level of uncertainty in the conditions at the site due to discharge estimation inaccuracies, debris, ice impacts, etc. Suggested values for the SF are: Condition SF Range Uniform flow conditions: Straight or mildly curving reach (curve 1.0 - 1.2 radius/channel width >30); impact from wave action and floating debris is minimal; little or no uncertainty in design parameters. Gradually varying flow: Moderate bend curvature (30 > curve 1.3 - 1.6 radius/channel width >10): impact from waves or floating debris moderate. Approaching rapidly varying flow: Sharp bend curvature (10 > 1.6 - 2.0 curve radius/channel width); significant impact potential from floating debris and/or ice; significant wind and/or boat generated waves (1 - 2 ft); high flow turbulence; turbulent mixing at bridge abutments; significant uncertainty in design parameters. 1 Thickness of Riprap. All stones should be contained reasonably well within the riprap layer thickness. The following criteria are given in HEC-11. 3 • It should not be less than the spherical diameter of the D100 stone or less than 1.5 times the spherical diameter of the D50 stone, whichever results in the greater thickness. • It should not be less than 1 ft for practical placement. • The thickness determined by either 1 or 2 should be increased by 50 percent when the riprap is placed underwater to compensate for uncertainties associated with this placement. • An increase in layer thickness of 0.5 to 1 ft, accompanied by an increase in stone sizes, should be made where the riprap will be subject to attack by floating debris, ice, or by waves from boat wakes, wind, or bedforms. Gradation of Riprap. The gradation of stones in riprap revetment affects the riprap's resistance to erosion. The stone should be reasonably well graded throughout the riprap layer thickness. Specifications should provide for two limiting gradation curves, and the stone gradation (as determined from a field test sample) should lay within these limits. The gradation limits should not be so restrictive that production costs would be excessive. HEC-11 presents suggested guidelines for establishing gradation limits (see Table 1-3-16). Table 1-3-16 and Table 1-3-17 present six suggested gradation classes based on AASHTO specifications (AASHTO 1999). © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-111 4 Roadway and Ballast Table 1-3-16. Rock Riprap Gradation Limits Stone Size Range m (ft) Stone Weight Range kg (lb) Percent of Gradation Smaller Than 1.5 D50 to 1.7 D50 3.0 W50 to 5.0 W50 100 1.2 D50 to 1.4 D50 2.0 W50 to 2.75 W50 85 1.0 D50 to 1.15 D50 1.0 W50 to 1.5 W50 50 0.4 D50 to 0.6 D50 0.1 W50 to 0.2 W50 15 Table 1-3-17. Riprap Gradation Classes (English) Riprap Class Rock Size1 (ft) Rock Size2 (lbs) Percent of Riprap Smaller Than Facing 1.30 0.95 0.40 200 75 5 100 50 10 Light 1.80 1.30 0.40 500 200 5 100 50 10 1/4 Ton 2.25 1.80 0.95 1,000 500 75 100 50 10 1/2 Ton 2.85 2.25 1.80 2,000 1,000 500 100 50 5 1 Ton 3.60 2.85 2.25 4,000 2,000 1,000 100 50 5 2 Ton 4.50 3.60 2.85 8,000 4,000 2,000 100 50 5 1Assuming 2Based a specific gravity of 2.65 on AASHTO gradations Gradation of the riprap being placed is controlled by visual inspection. To aid the inspector's judgment, two or more samples of riprap of the specified gradation should be prepared by sorting, weighing, and remixing in proper proportions. Each sample should weigh about 5 to 10 tons. One sample should be placed at the quarry and one sample at the construction site. The sample at the construction site could be part of the finished riprap blanket. These samples should be used as a frequent reference for judging the gradation of the riprap supplied. Filter Systems. A filter system should be provided to prevent the migration of the fine soil between the voids of the riprap. The system may be either a granular filter or an engineering filter fabric. Consultation with a geotechnical engineer may be useful in making the proper selection. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-112 AREMA Manual for Railway Engineering Natural Waterways Granular Filters. In using a granular filter system, the filter ratio as stated in the following relationships should be met. EQ 31 The left side of the inequality in EQ 31 is intended to prevent erosion (piping) through the filter and the center portion provides for adequate permeability for structural bedding. The right portion provides a uniformity criterion. If a single layer of filter will not satisfy the equation, two or more layers must be used. The filter requirement applies between the bank material and the filter as well as the filter and the riprap. The thickness of the filter blanket should be from 150 mm (6 in) and 380 mm (15 in) for a single layer, or from 100 mm (4 in) to 200 mm (8 in) for individual layers of a multilayer installation. Engineering Fabric Filters. For the proper design of a geotextile filter system, see Holtz et al. (FHWA HI-95038). The fabric should provide drainage and filtration. Therefore, both functions should be considered in the selection of the filter material. Edge Treatment. To prevent undermining at the toe and flanks of the riprap, special edge treatment may be required such as: 1 • Extending the lower toe of the riprap below the anticipated contraction scour and long-term degradation depth. • Placing launchable stone at the toe of the installation that will slide into the scour hole as it develops. This method requires extra material to be placed at bottom of the installation in a trench or extending into the stream (Figure 1-3-51 and Figure 1-3-52). For additional information, see HEC-11. • The flanks may be protected as illustrated in Figure 1-3-53. In Section A-A, the area shown as "compacted backfill" may be completely filled with riprap. 3 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-113 Roadway and Ballast Figure 1-3-51. Methods of Providing Toe Protection (USACE 1991) Revetment Riprap Design Example The following design example illustrates the general revetment riprap design procedure. From a field survey of the site and an analysis of the stream using a water surface profile program such as HEC-RAS the following data have been established. Given: Channel width = 300 ft Bend radius = 200 ft Average velocity in main channel (Va) = 12.6 fps Average depth in main channel (da) = 12 ft Available rock riprap has a specific gravity of 2.60 and is considered angular. A 1 vertical to 2 horizontal (1V:2H) bank slope is to be used. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-114 AREMA Manual for Railway Engineering Natural Waterways 1 3 4 Figure 1-3-52. Alternative Method of Providing Toe Protection (HEC-11) © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-115 Roadway and Ballast Figure 1-3-53. Flank Details (HEC-11) Solution: Using EQ 28, EQ 29, and EQ 30, the following size is established. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-116 AREMA Manual for Railway Engineering Natural Waterways 3 D 50 K u CV a = --------------------------------0.5 1.5 d avg K 1 2 0.5 sin K 1 = 1 – -------------2 sin 1.5 1.61 SF C = ------------------------------1.5 Ss – 1 EQ 32 From Figure 1-3-46 for angular stone, a value of 41 for the angle of repose would be a good initial estimate to use. For a side slope of 1V:2H: 2 0.5 sin K 1 = 1 – --------------2 sin 2 0.5 0.447 = 1 – ---------------------2 0.656 = 0.73 Assuming for a gradually varying flow with moderate bend curvature, the stability factor (SF) is 1.6. (See the previous guidance for stability factor.) 1.5 1.5 1.61 SF 1.61 1.6 C = ------------------------------- = -------------------------------- = 1.61 1.5 1.5 Ss – 1 2.60 – 1 1 The required stone size is then found. 3 Using this stone size of 1.5 ft, recheck the angle of repose. It would be close to the original 41 that was assumed and would be acceptable. Taking this computed size of stone, compare it to a class of riprap that is available and use the next larger size (perhaps the AASHTO 1/4 ton class riprap). The layer thickness would be twice the mean size (2 D50) or the thickness equal to the D100. The need for a filter system depends on the parent material at the site. Normally a filter system will be required. It may be either a granular filter or a geotextile. Rock-Fill Trenches and Windrow Revetment Rock-fill trenches are structures used to protect banks from caving caused by erosion at the toe. A trench is excavated along the toe of the bank and filled with rocks as shown in Figure 1-3-54. The size of trench to hold the rock fill depends on expected depths of scour. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-117 4 Roadway and Ballast Figure 1-3-54. Rock-fill Trench (after HDS 6) As the streambed adjacent to the toe is eroded, the toe trench is undermined and the rock fill slides downward to pave the bank. It is advantageous to grade the banks before placing riprap on the slope and in the toe trench. The slope should be at such an angle that the saturated bank is stable while the stream stage is falling. An alternative to a rock-fill trench at the toe of the bank is to excavate a trench above the water line along the top of the bank and fill the trench with rocks. As the bank erodes, stone material in the trench is added on an as-needed basis until equilibrium is established. This method is applicable in areas of rapidly eroding banks of medium to large size streams. Windrow revetment (Figure 1-3-55) consists of a supply of rock deposited along an existing bank line at a location beyond which additional erosion is to be prevented. When bank erosion reaches and undercuts the supply of rock, it falls onto the eroding area, thus giving protection against further undercutting. The resulting bank line remains in a near natural state with an irregular appearance due to intermittent lateral erosion in the windrow location. The treatment particularly lends itself to the protection of adjacent wooded areas, or placement along stretches of presently eroding, irregular bank line. The effect of windrow revetment on the interchange of flow between the channel and overbank areas and flood flow distribution in the flood plain should be carefully evaluated. Windrow installations will perform as guide banks or levees and may adversely affect flow distribution at bridges or cause local scour. Tying the windrow to the embankment at an abutment would be contrary to the purpose of the windrow since the rock is intended to fall into the channel as the bank erodes. This would potentially expose the abutment. The following observations and conclusions from model investigations of windrow revetments and rock-fill trenches may be used as design guidance. More definitive guidance is not presently available (USACE 1981). • The application rate of stone is a function of channel depth, bank height, material size, and estimated bed scour. • A triangular windrow is the least desirable shape, a trapezoidal shape provides a uniform blanket of rock on an eroding bank, and a rectangular shape provides the best coverage. A rectangular shape is most easily placed in an excavated trench. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-118 AREMA Manual for Railway Engineering Natural Waterways 1 3 4 Figure 1-3-55. Windrow Revetment, Definition Sketch (after USACE 1981) • Bank height does not significantly affect the final revetment; however, high banks tend to produce a nonuniform revetment alignment. Large segments of bank tend to break loose and rotate slightly on high banks, whereas low banks simply "melt" or slough into the stream. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-119 Roadway and Ballast • Stone size influences the thickness of the final revetment, and a smaller gradation of stone forms a more dense, closely chinked protective layer. Stones must be large enough to resist being transported by the stream, and a well-graded stone should be used to ensure that the revetment does not fail from leaching of the underlying bank material. Large stone sizes require more material than smaller stone sizes to produce the same relative thickness of revetment. In general, the greater the stream velocity, the steeper the side slope of the final revetment. The final revetment slope will be about 15 percent flatter than the initial bank slope. • A windrow segment should be extended landward from the upstream end to reduce the possibility of outflanking of the windrow. Rigid Revetments Rigid revetments are generally smoother than flexible revetments and thus improve hydraulic efficiency and are generally highly resistant to erosion and impact damage. They are susceptible to damage from the removal of foundation support by subsidence, undermining, hydrostatic pressures, slides, and erosion at the perimeter. They are also among the most expensive streambank protection countermeasures. Concrete Pavement Concrete paving should be used only where the toe can be adequately protected from undermining and where hydrostatic pressures behind the paving will not cause failure. This might include impermeable bank materials and portions of banks which are continuously under water. Sections intermittently above water should be provided with weep holes. Refer to HEC-11 for design of concrete pavement revetment. Sacks Burlap sacks filled with soil or sand-cement mixtures have long been used for emergency work along levees and streambanks during floods (Figure 1-3-56). Commercially manufactured sacks (burlap, paper, plastics, etc.) have been used to protect streambanks in areas where riprap of suitable size and quality is not available at a reasonable cost. Sacks filled with sand-cement mixtures can provide long-term protection if the mixture has set up properly, even though most types of sacks are easily damaged and will eventually deteriorate. Sand-cement sack revetment construction is not economically competitive in areas where good stone is available. However, where quality riprap must be transported over long distances, sack revetment can often be placed at a lesser cost than riprap. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-120 AREMA Manual for Railway Engineering Natural Waterways Figure 1-3-56. Typical Sand-cement Bag Revetment (after Brown 1985) If a sack revetment is to be constructed, the sacks should be filled with a mixture of 15 percent cement (minimum) and 85 percent dry sand (by weight). The filled sacks should be placed in horizontal rows like common house brick beginning at an elevation below any toe scour (alternatively, riprap can be placed at the toe to prevent undermining of the bank slope). The successive rows should be stepped back approximately onehalf-bag width to a height on the bank above which no protection is needed. The slope of the completed revetment should not be steeper than 1:1. After the sacks have been placed on the bank, they can be wetted down for a quick set or the sand-cement mixture can be allowed to set up naturally through rainfall, seepage or condensation. If cement leaches through the sack material, a bond will form between the sacks and prevent free drainage. For this reason, weepholes should be included in the revetment design. The installation of weepholes will allow drainage of groundwater from behind the revetment thus helping to prevent a pressure buildup that could cause revetment failure. This revetment requires the same types of toe protection as other types of rigid revetment. 1 3 References for Revetment Design AASHTO, 1999. "Model Drainage Manual," Metric Edition, American Association of State Highway and Transportation Officials, Washington, D.C. Brown, S.A., 1985. "Streambank Stabilization Measures for Highway Engineers," FHWA/RD-84, 100 Federal Highway Administration, McLean, VA. Brown, S.A. and Clyde, E.S., 1989. "Design of Riprap Revetment," Hydraulic Engineering Circular No.11, FHWA-IP-89-016. Prepared for the Federal Highway Administration, Washington, D.C. Chen, Y.H. and Cotton, G.K., 1988. "Design of Roadway Channels with Flexible Linings," U.S. Department of Transportation, Federal Highway Administration, FHWA IP87-7, NTIS PB89-122584, Hydraulic Engineering Circular No. 15. Holtz, D.H., Christopher, B.R., and Berg, R.R., 1995. "Geosynthetic Design and Construction Guidelines," National Highway Institute, Publication No. FHWA HI-95-038, Federal Highway Administration, Washington, D.C., May. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-121 4 Roadway and Ballast Hydrologic Engineer Center, 2001. "HEC-RAS River Analysis System," Hydraulic Reference Manual, Version 3.0, U.S. Army Corps of Engineers, Davis, CA. Lagasse, P.F., Zevenbergen, L.W., Schall, J.D., and Clopper, P.E., 2001. "Bridge Scour and Stream Instability Countermeasures – Experience, Selection, and Design Guidelines," Second Edition, Report FHWA NHI 01-003, Federal Highway Administration, Hydraulic Engineering Circular No. 23, U.S. Department of Transportation, Washington, D.C. Richardson, E.V., Simons, D.B., and Lagasse, P.F., 2001. "River Engineering for Highway Encroachments Highways in the River Environment," Report No. FHWA NHI 01-004, Hydraulic Design Series No. 6, Federal Highway Administration, Washington, D.C. U.S. Army Corps of Engineers, 1981. "The Streambank Erosion Control Evaluation and Demonstration Act of 1974," Final Report to Congress, Executive Summary and Conclusions. U.S. Army Corps of Engineers, 1991. "Hydraulic Design of Flood Control Channels," EM 1110-2-1601, Department of the Army, Washington, D.C. 3.6.4.6 Wire-Enclosed Rock Wire-enclosed rock (gabion) revetments consist of rectangular wire mesh baskets filled with rock. The most common types of wire-enclosed revetments are mattresses and stacked blocks. The wire cages which make up the mattresses and gabions are available from commercial manufacturers. If desired, the wire baskets can also be fabricated from available wire fencing materials. This section provides design guidance for stacked block gabion revetment. Reference to HEC-11 is suggested for design guidance on gabion mattresses. As a revetment, wire-enclosed rock has limited flexibility. They will flex with bank surface subsidence; however, if excessive subsidence occurs, the baskets will span the void until the stresses in rock-filled baskets exceed the tensile strength of wire strands. At this point, the baskets will fail (Escarameia 1998). The conditions under which wire-enclosed rock is applicable are similar to those of other revetments. However, their economic use is limited to locations where the only rock available economically is too small for use as rock riprap slope protection. The primary advantages of wire-enclosed rock revetments include: Their ability to span minor pockets of bank subsidence without failure The ability to use smaller, lower quality, and less dense, rock in the baskets Disadvantages of the use of wire-enclosed rock revetments include: Susceptibility of the wire baskets to corrosion and abrasion damage High labor costs associated with fabricating and filling the wire baskets More difficult and expensive repair than standard rock protection Less flexibility than standard rock protection The most common failure mechanism of wire basket revetments has been observed to be failure of the wire baskets. Failure from abrasion and corrosion of the wire strands has even been found to be a common problem when the wire is coated with plastic. The plastic coating is often stripped away by abrasion from sand, gravel, cobbles, or other sediments carried in natural stream flows (particularly at and near flood stages). Once the wire has been broken, the rock in the baskets is usually washed away. To avoid the problem of abrasion and © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-122 AREMA Manual for Railway Engineering Natural Waterways corrosion of the wire baskets, it is recommended that wire-enclosed rock revetments not be used on lower portions of the channel bank in environments subject to significant abrasion or corrosion. An additional failure mechanism has been observed when the wire basket units are used in high-velocity, steepslope environments. Under these conditions, the rock within individual baskets shifts downstream, deforming the baskets as the material moves. The movement of material within individual baskets will sometimes result in exposure of filter or base material. Subsequent erosion of the exposed base material can cause failure of the revetment system. Stacked Block Gabions Stacked block gabion revetments consist of rectangular wire baskets which are filled with stone and stacked in a stepped-back fashion to form the revetment surface (Figure 1-3-57). They are also commonly used at the toe of embankment slopes as toe walls which help to support other upper bank revetments and prevent undermining. As illustrated in Figure 1-3-57, the rectangular basket or gabion units used for stacked configurations are more equidimensional than those typically used for mattress designs. That is, they typically have a square cross section. Commercially available gabions used in stacked configurations include those listed in Table 1-3-18 having 3-foot widths and thickness. Other commercially available sizes can also be used in the stacked block configurations. Conceptually, the gabion units for stacked block configurations could also be fabricated from available fencing materials. However, the labor intensive nature of such an installation makes it impractical in most cases. Therefore, only commercially available units are considered in the following design guidelines. 1 Design Guidelines for Stacked Block Gabions Components of stacked gabion revetment design include layout of a general scheme or concept, bank and foundation preparation, unit size and configuration, stone size and quality, edge treatment, backfill and filter considerations, and basket or rock enclosure fabrication. Design guidelines for stone size and quality, and bank preparation are generally available from manufacturer's literature (see also HEC-11). General: Stacked gabion revetments are typically used when the slope to be protected is greater than 1:1 or when the purpose of the revetment is for flow training. They can also be used as retaining structures when space limitations prohibit bank grading to a slope suitable for other revetments. Typical design schemes include flow training walls, Figure 1-3-57(a), and low or high retaining walls (Figure 1-3-57(b) and (c), respectively. Stacked gabion revetments must be based on a firm foundation. The foundation or base elevation of the structure should be well below any anticipated scour depth. Additionally, in alluvial streams where channel bed fluctuations are common, an apron should be used as illustrated in Figure 1-3-57(a) and (b). Aprons are also recommended for situations where the estimated scour depth is uncertain. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-123 3 4 Roadway and Ballast Figure 1-3-57. Typical Stacked Block Gabion Revetment Details (a) training well with counterforts, (b) stepped back low retaining wall with apron; (c) high retaining wall, stepped-back configuration; (d) high retaining wall, batter type Table 1-3-18. Standard Gabion Sizes Thickness (ft) Width (ft) Length (ft) Wire-Mesh Opening Size (in x in) 0.75 6 9 2.5 x 3.25 0.75 6 12 2.5 x 3.25 1. 3 6 3.25 x 4.5 1. 3 9 3.25 x 4.5 1. 3 12 3.25 x 4.5 1.5 3 6 3.25 x 4.5 1.5 3 9 3.25 x 4.5 1.5 3 12 3.25 x 4.5 3 3 6 3.25 x 4.5 3 3 9 3.25 x 4.5 3 3 12 3.25 x 4.5 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-124 AREMA Manual for Railway Engineering Natural Waterways Size and Configuration: Common commercial sizes for stacked gabions are listed in Table 1-3-18. The most common sizes used are those having widths and depths of 3 ft. Sizes less than 1 ft thick are not practical for stacked gabion installations. Typical design configurations include flow training walls and structural retaining walls. The primary function of flow training walls (Figure 1-3-57(a)) is to establish normal channel boundaries in rivers where erosion has created a wide channel, or to realign the river when it is encroaching on an existing or proposed structure. A stepped-back wall is constructed at the desired bank location and counterforts are installed to tie the walls to the channel bank at regular intervals as illustrated. The counterforts are installed to form a structural tie between the training wall and the natural stream bank, and to prevent overflow from scouring a channel behind the wall. Counterforts should be spaced to eliminate the development of eddy or other flow currents between the training wall and the bank which could cause further erosion of the bank. The dead water zones created by the counterforts so spaced will encourage sediment deposition behind the wall which will enhance the stabilizing characteristics of the wall. Retaining walls can be designed in either a stepped-back configuration as illustrated in Figure 1-3-57(b) and (c), or a batter configuration as illustrated in Figure 1-3-57(d). Structural details and configurations can vary from site to site. Gabion walls are gravity structures and their design follows standard engineering practice for retaining structures. Design procedures are available in standard soil mechanics texts as well as in gabion manufacturer's literature. Edge Treatment: The flanks and toe of stacked block gabion revetments require special attention. The upstream and downstream flanks of these revetments should include counterforts, see Figure 1-3-57(a). The counterforts should be placed 12 to 18 ft from the upstream and downstream limits of the structure, and should extend a minimum of 12 ft into the bank. 1 The toe of the revetment should be protected by placing the base of the gabion wall at a depth below anticipated scour depths. In areas where it is difficult to predict the depth of expected scour, or where channel bed fluctuations are common, it is recommended that a mattress apron be used. The minimum apron length should be equal to 1.5 times the anticipated scour depth below the apron. This length can be increased in proportion to the level of uncertainty in predicting the local toe scour depth. 3 Backfill/Filter Requirements: Standard retaining wall design requires the use of selected backfill behind the retaining structure to provide for drainage of the soil mass behind the wall. The permeable nature of gabion structures permits natural drainage of the supported embankment. However, since material leaching through the gabion wall can become trapped and cause plugging, it is recommended that a granular backfill material be used, see Figure 1-3-57(d). The backfill should consist of a 2- to 12-inch (5.1- to 30.5-cm) layer of graded crushed stone backed by a layer of fine granular backfill. 4 Basket Fabrication: Commercially fabricated basket units are formed from galvanized steel wire mesh of triple twist hexagonal weave. The netting wire and binding wire specifications are the same discussed for mattress units. Specifications for galvanizing and PVC coatings are also the same for block designs as for mattresses. Figure 1-3-58 illustrates typical details of basket fabrication. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-125 Roadway and Ballast Figure 1-3-58. Gabion Basket Fabrication Construction Construction details for gabion installations typically vary with the design and purpose for which the protection is being provided. Several typical design schematics are presented in Figure 1-3-57 and Figure 1-3-58. As with mattress designs, fabrication and filling of individual basket units can be done at the site, or at an offsite location. The most common practice is to fabricate and fill individual gabions at the design site. The following steps outline the typical sequence used for installing a stacked gabion revetment or wall: Step 1. Prepare the revetment foundation. This includes excavation for the foundation and revetment wall. Step 2. Place the filter and gabion mattress (for designs which incorporate this component) on the prepared grade, then sequentially stack the gabion baskets to form the revetment system. Step 3. Each basket is unfolded and assembled by lacing the edges together and the diaphragms to the sides. Step 4. Fill the gabions to a depth of 1-foot with stone form 4 to 12 inches in diameter. Place one connecting wire in each direction and loop it around two meshes of the gabion wall. Repeat this operation until the gabion is filled. Step 5. Wire adjoining gabions together by their vertical edges; stack empty gabions on the filled gabions and wire them at front and back. Step 6. After the gabion is filled, fold the top shut and wire it to the ends, sides and diaphragms. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-126 AREMA Manual for Railway Engineering Natural Waterways Step 7. Crushed stone and granular backfill should be placed in intervals to help support the wall structure. It is recommended that backfill be placed at 3-course intervals. References for Wire Enclosed Rock Brown, S.A. and Clyde, E.S., 1989. "Design of Riprap Revetment," Hydraulic Engineering Circular No.11, FHWA-IP-89-016. Prepared for the Federal Highway Administration, Washington, D.C. Escarameia, M., 1998. "River and Channel Revetments – A Design Manual," Thomas Telford Limited, London. 3.6.4.7 Check Dams/Drop Structures Background Check dams or channel drop structures are used downstream of bridge crossings to arrest head cutting and maintain a stable streambed elevation in the vicinity of the bridge. Check dams are usually built of rock riprap, concrete, sheet piles, gabions, or treated timber piles. The material used to construct the structure depends on the availability of materials, the height of drop required, and the width of the channel. Rock riprap and timber pile construction have been most successful on channels having small drops and widths less than 100 ft. Sheet piles, gabions, and concrete structures are generally used for larger drops on channels with widths ranging up to 300 ft. Check dam location with respect to the bridge depends on the hydraulics of the bridge reach and the amount of headcutting or degradation anticipated. Check dams can initiate erosion of banks and the channel bed downstream of the structure as a result of energy dissipation and turbulence at the drop. This local scour can undermine the check dam and cause failure. The use of energy dissipators downstream of check dams can reduce the energy available to erode the channel bed and banks. In some cases it may be better to construct several consecutive drops of shorter height to minimize erosion. Concrete lined basins as discussed later may also be used. 1 Lateral erosion of channel banks just downstream of drop structures is another adverse result of check dams and is caused by turbulence produced by energy dissipation at the drop, bank slumping from local channel bed erosion, or eddy action at the banks. Bank erosion downstream of check dams can lead to erosion of bridge approach embankments and abutment foundations if lateral bank erosion causes the formation of flow channels around the ends of check dams. The usual solution to these problems is to place riprap revetment on the streambank adjacent to the check dam (see Article 3.6.4.5). 3 Erosion of the streambed can also be reduced by placing rock riprap in a preformed scour hole downstream of the drop structure. A row of sheet piling with top set at or below streambed elevation can keep the riprap from moving downstream. Because of the problems associated with check dams, the design of these countermeasures requires designing the check dams to resist scour by providing for dissipation of excess energy and protection of areas of the bed and the bank which are susceptible to erosive forces. 4 Bed Scour For Vertical Drop Structures Estimating Bed Scour. The most conservative estimate of scour downstream of channel drop structures is for vertical drops with unsubmerged flow conditions. For the purposes of design the maximum expected scour can be assumed to be equal to the scour for a vertical, unsubmerged drop, regardless of whether the drop is actually sloped or is submerged. A sketch of a typical vertical drop structure with a free overfall is shown in Figure 1-3-59. An equation developed by the Bureau of Reclamation (USBR) is recommended to estimate the depth of scour downstream of a vertical drop: © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-127 Roadway and Ballast Figure 1-3-59. Schematic of a Vertical Drop Caused by a Check Dam ds = K u Ht 0.225 0.54 q EQ 33 – dm where: ds = local scour depth for a free overall, measured from the streambed downstream of the drop, m (ft) q = discharge per unit width, m3/s/m (cfs/ft) Ht = total drop in head, measured from the upstream to the downstream energy grade line, m (ft) dm, Yd = tailwater depth, m (ft) Ku = 1.90 (SI) Ku = 1.32 (English) It should be noted that Ht is the difference in the total head from upstream to downstream. This can be computed using the energy equation for steady uniform flow: EQ 34 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-128 AREMA Manual for Railway Engineering Natural Waterways where: Y = depth, m (ft) V = velocity, m/s (ft/s) Z = bed elevation referenced to a common datum, m (ft) g = acceleration due to gravity 9.81 m/s2 (32.2 ft/s2) The subscripts u and d refer to upstream and downstream of the channel drop, respectively. The depth of scour as estimated by the above equation is independent of the grain size of the bed material. This concept acknowledges that the bed will scour regardless of the type of material composing the bed, but the rate of scour depends on the composition of the bed. In some cases, with large or resistant material, it may take years or decades to develop the maximum scour hole. In these cases, the design life of the bridge may need to be considered when designing the check dam. The check dam must be designed structurally to withstand the forces of water and soil assuming that the scour hole is as deep as estimated using the equation above. Therefore, the designer should consult geotechnical and structural engineers so that the drop structure will be stable under the full scour condition. In some cases, a series of drops may be employed to minimize drop height and construction costs of foundations. Riprap or energy dissipation could be provided to limit depth of scour (see, for example, Peterka and HEC-14). 1 Check Dam Design Example Given: Channel degradation is threatening bridge foundations. Increasing the bed elevation 4.6 ft will stabilize the channel at the original bed level. A drop structure will raise the channel bed and reduce upstream channel slopes, resulting in greater flow depths and reduced velocity upstream of the structure. For this example, as illustrated by Figure 1-3-60, the following hydraulic parameters are used: Design Discharge Q = 5,900 ft3/s Channel Width B = 105 ft Upstream Water Depth Yu = 10.6 ft Tail Water Depth dm, Yd = 9.5 ft Unit Discharge q = 56.2 ft3/s/ft Upstream Mean Velocity Vu = 5.3 ft/s Downstream Mean Velocity Vd = 5.9 ft/s Drop Height h = 4.6 ft 4 Solution: Ht is calculated from the energy equation. Using the downstream bed as the elevation datum gives: © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 3 1-3-129 Roadway and Ballast EQ 35 Using EQ 33, the estimated depth of scour below the downstream bed level is: ds = K u Ht 0.225 0.54 q – dm EQ 36 Figure 1-3-60. Design Example of Scour Downstream of a Drop Structure d s = 1.32 5.6 0.225 56.2 0.54 – 9.5 In this case, the unsupported height of the structure is (h + ds) or 12.2 ft. If, for structural reasons, this height is unacceptable, then either install riprap to limit scour depth or a series of check dams could be constructed. It should be noted that if a series of drops are required, adequate distance between each drop must be maintained. Lateral Scour Downstream of Check Dams Lateral scour of the banks of a stream downstream of check dams can cause the streamflow to divert around the check dam. If this occurs, a head cut may move upstream and endanger the railroad crossing. To prevent © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-130 AREMA Manual for Railway Engineering Natural Waterways this the banks of the stream must be adequately protected using riprap or other revetments. Riprap should be sized and placed in a similar fashion as for spurs and guide banks. The designer is referred to HEC-11 for proper sizing, and placement of riprap on the banks. Revetments are discussed in Article 3.6.4.5. References for Check Dam Design Brown, S.A. and Clyde, E.S., 1989. "Design of Riprap Revetment," Hydraulic Engineering Circular No.11, FHWA-IP-89-016. Prepared for the Federal Highway Administration, Washington, D.C. Federal Highway Administration, 1983. "Hydraulic Design of Energy Dissipators for Culverts and Channels," Hydraulic Engineering Circular Number 14, U.S. Department of Transportation, Washington, D.C. Lagasse, P.F., Zevenbergen, L.W., Schall, J.D., and Clopper, P.E., 2001. "Bridge Scour and Stream Instability Countermeasures – Experience, Selection, and Design Guidelines," Second Edition, Report FHWA NHI 01-003, Federal Highway Administration, Hydraulic Engineering Circular No. 23, U.S. Department of Transportation, Washington, D.C. Pemberton, E.L. and Lara, J.M., 1984. "Computing Degradation and Local Scour," Technical Guidelines for Bureau of Reclamation, Engineering Research Center, Denver, CO, January. Peterka, A.J., 1964. "Hydraulic Design of Stilling Basins and Energy Dissipators," Engineering Monograph No. 25, Bureau of Reclamation, Division of Research, Denver, CO. 1 3.6.4.8 Channel Cutoffs Design Considerations For some railroad encroachments, a change in the river channel alignment is advantageous. When a river crossing site is so constrained by non-hydraulic factors that consideration of alternative sites is not possible, the engineer must attempt to improve the local situation to meet specific needs. Also, the engineer may be forced to make channel improvements in order to maintain and protect existing embankment in or adjacent to the river. Suppose a meandering river is to be crossed with the alignment, as shown in Figure 1-3-61(a). Assume that the alignment is fixed by constraints in the acquisition of the right-of-way. To create better flow alignment with the bridge, consideration is given to channel improvement as shown in Figure 1-3-61(b). Similarly, consideration for improvement to the channel would also be advisable for a hypothetical lateral encroachment of a roadway as depicted in Figure 1-3-61(c). In either case, the designer's questions are how to realign the channel, and what criteria to use to establish stable channel dimensions. Prior to realigning a river channel the stability of the existing channel must be examined. A stream classification, recent and past aerial photographs and field surveys are generally necessary (see Article 3.4.5). The realigned channel may be made straight without curves, or may include one or more curves. If curves are included, the radii of curvature, the number of bends, the limits of rechannelization (hence the length or slope of the channel) and the cross-sectional area are decisions which have to be made by the designer. Different rivers have different characteristics and historical background with regard to channel migration, discharge, stage, geometry and sediment transport. As indicated in the previous chapters, it is important for the designer to understand and appreciate river hydraulics and geomorphology when making decisions concerning channel relocation. It is difficult to state generalized criteria for channel relocation applicable to every river. Knowledge about river systems has not yet advanced to such a state as to make this possible. Nevertheless, it is possible to provide some principles and guidelines for the design engineer. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-131 3 4 Roadway and Ballast Figure 1-3-61. Encroachment on a Meandering River As the general rule, the radii of bends (Rc) as shown in Figure 1-3-61(a) should be made about equal to the mean radii of bends in extended reaches of the river. When the angle defined in Figure 1-3-61(a) exceeds about 40 degrees, this provides a sufficient crossing length for the thalweg to shift from one side of the channel to the other. Generally, it is necessary to stabilize the outside banks of the curves in order to hold the new alignment, and depending upon crossing length some amount of maintenance may be necessary to remove sandbars after large floods so that the channel does not develop new meander patterns in the crossings during normal flows. Any designed increase in width should be limited to about 10 to 15 percent. Wider channels would be ineffective. Deposition would occur along one bank and the effort of extra excavation would be wasted. Furthermore, bar formation would be encouraged, with resultant tendencies for changes in the meander pattern leading to greater maintenance costs for bank stabilization and removal of the bars to hold the desired river alignment. The depth of flow in the channel is dependent on discharge, effective channel width, sediment transport rate (because it affects bed form and channel roughness) and channel slope. This discussion pertains to alluvial channels with silt and sand sized bed materials. For streams with gravel and cobble beds, the usual concern is to provide adequate channel cross-sectional dimensions to convey flood flows. If the realigned channels are made too steep, there is an increase in transport rate of the bed material. The deposition of material in the reaches downstream of the crossing tends to form gravel bars and encourages changes in the planform of the channel. Short-term changes in channel slope can be expected until equilibrium is reestablished over extended reaches both upstream and downstream of the rechannelized reach. Bank stabilization may be necessary to prevent lateral migration, and periodic removal of gravel bars may also be necessary. Assessment of Stability for Relocated Streams Brice (1980) reported case histories for channel stability of relocated streams in different regions of the United States. Based on his study, the recommendations and conclusions presented here apply to specific aspects of the planning and construction of channel relocation. They are intended for assessment of the risk of instability © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-132 AREMA Manual for Railway Engineering Natural Waterways and for reduction of the degree of instability connected with relocation. Serious instability resulting from relocation can be observed either when the prior natural channel is unstable or when floods of high recurrence interval occur during or soon after construction. Although there is an element of uncertainty in channel stability, the experience represented by Brice's study sites provides useful guidelines for improvement in the performance of relocated channels. Channel Stability Prior To Relocation. Assessment of the stability of a channel prior to relocation is needed to assess erosion-control measures and risk of instability. An unstable channel is likely to respond unfavorably to relocation. Bank stability is assessed by field study and the stereoscopic examination of aerial photographs. The most useful indicators of bank instability are cut or slumped banks, fallen trees along the bankline, and wide, unvegetated, exposed point bars. Bank recession rates are measured by comparison of time-sequential aerial photographs. Vertical instability is equally important but more difficult to determine. It is indicated by changes in channel elevation at bridges and gaging stations. Serious degradation is usually accompanied by generally cut or slumped banks along a channel. Erosion Resistance Of Channel Boundary Materials. The stability of a channel, whether natural or relocated, is partly determined by the erosion resistance of materials that form the wetted perimeter of the channel. Resistant bedrock outcrops, which extend out into the channel bottom, or that lie at shallow depths, will provide protection against degradation. Not all bedrock is resistant. Erosion of shale, or of other sedimentary rock types interbedded with shale, has been observed. Degradation was slight or undetected at most sites where bed sediment was of cobble and boulder size. However, serious degradation may result from relocation. Degradation may result from the relocation of any alluvial channel, whatever the size of bed material, but the incidence of serious degradation of relocated channels is slight. The cohesion and erosion resistance of banks tend to increase with clay content. Banks of weakly coherent sand or silt are clearly subject to rapid erosion, unless protected with vegetation. No consistent relation was found between channel stability and the cohesion of bank materials, probably because of the effects of vegetation. Length Of Relocation. The length of relocation contributes significantly to channel instability at sites where its value exceeded 250 channel widths. When the value is below 100 channel widths, the effects of length of relocation are dominated by other factors. The probability of local bank erosion at some point along a channel increases with the length of the channel. The importance of vegetation, both in appearance and in erosion control, would seem to justify a serious and possibly sustained effort to establish it as soon as possible on the graded banks. Bank Revetment. Revetment makes a critical contribution to stability at many sites where it is placed at bends and along embankments. Rock riprap is by far the most commonly used and effective revetment (see Article 3.6.4.5). Check Dams (drop structures). In general, check dams are effective in preventing channel degradation (see Article 3.6.4.7). The potential for erosion at a check dam depends on its design and construction, its height and the use of revetment on adjoining banks. A series of low check dams, less than about 2 ft in height, is probably preferable to a single higher structure, because the potential for erosion and failure is reduced. One critical problem arising with check dams relates to improper design for large flows. Higher flows have worked around the ends of many installations to produce failure. Maintenance. The following problems that can be controlled by maintenance were observed along relocated channels: (1) growth of annual vegetation in channel; (2) reduction of channel conveyance by overhanging trees; (3) local bank cutting; and (4) bank slumping. The expense of routine maintenance or inspection of relocated channels beyond the right-of-way is probably prohibitive. However, most of the serious problems could be detected by periodic inspection, perhaps by aerial photography, during the first 5 or 10 years after construction. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-133 1 3 4 Roadway and Ballast Relationship Between Sinuosity And Stability. This relationship is summarized as follows: (1) Meandering does not necessarily indicate instability; an unstable stream will not remain highly sinuous for very long, because the sinuosity will be reduced by frequent meander cutoffs; (2) Where instability is present along a reach, it occurs mainly at bends; straight segments may remain stable for decades; and (3) The highest instability is for reaches whose sinuosity is in the range of 1.2 to 2 and whose type is either wide bend or braided point bar. River Response to Cutoffs The following three conceptual examples provide a summary of river response to cutoffs. In Table 1-3-19, each individual case is identified in the first column to show the physical situation that exists prior to the cutoff. In the following three columns some of the major effects (local, upstream, and downstream) resulting from the cutoff at a particular crossing are given. Case (1) illustrates a situation where artificial cutoffs have straightened the channel downstream of a particular crossing. Straightening the channel downstream of the crossing significantly increases the channel slope. This causes higher velocities, increased bed material transport, degradation and possible head cutting in the vicinity of the structure. This can result in unstable river banks and a braided streamform. The straightening of the main channel can drop the base level, adversely affecting tributary streams flowing into the straightened reach of the main channel. Case (2) illustrates a situation where the main channel is realigned in the vicinity of the bridge crossing. A cutoff is made to straighten the main channel through the selected bridge site. As discussed in Case (1), increased local gradient, local velocities, local bed material transport, and possible changes in the characteristics of the channel are expected due to the new conditions. As a result the channel may braid. A short cut off section (1 or 2 bends) can be designed to transport the same sediment loads that the river is capable of carrying upstream and downstream of the straightened reach; however, it may be difficult to achieve stability when multiple bends in a long reach are cut off. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-134 AREMA Manual for Railway Engineering Natural Waterways Table 1-3-19. River Response to Cutoffs (HDS 6) Bridge Location Local Effects 1 - Steeper slope Upstream Effects Downstream Effects See local effects 1 - Deposition downstream of straightened channel 2 - Higher velocity 2 - Increase in flood stage 3 - Increased transport 4 - Degradation and possible headcutting 3 - Loss of channel capacity 5 - Banks unstable 4 - Degradation in tributary 6 - River may braid (1) Cutoffs downstream of crossing 7- Danger to bridge foundation from degradation and local scour 1 - None if straight section is designed to transport the sediment load of the river and if it is designed to be stable when subjected to anticipated flow. Otherwise same as in Case (1) above 1 - Similar to local effects 1 - Similar to local effects 1 (2) River channel relocation at crossing site 3 1 - Energy gradient also increased in the reach upstream and may cause 2 - Highway fill is subject change of river form to scour as channel tends from meandering to braided to shift to old alignment 1 - Increased energy gradient and potential bank and bed scour 3 - Reach is subject to bed degradation as headcut develops at the downstream end and travels upstream 4 - Lateral drainage into the river is interrupted and may cause flooding and erosion (3) Longitudinal encroachment 2 - Rate of sediment transport is increased. As the headcut travels upstream severe bank and bed erosion is possible 1 - Channel will aggrade as the sediment load coming from bed and bank erosion is received 2 - Channel may deteriorate from meandering to braided 3 - If tributaries in the zone of influence exist they will respond to lowering of base level © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-135 4 Roadway and Ballast It is possible to build modified reaches of main channels that do not introduce major adverse responses due to local steepening of the main channel. In order to design a straightened channel so that it behaves essentially as the natural channel in terms of velocities and magnitude of bed material transport, it is usually necessary to build a wider, shallower section. Case (3) illustrates an example of longitudinal encroachment. Here, a few bends of a meandering stream have been realigned to accommodate a railroad (see Case 2). There are two problems involved in channel realignment. First, the length of realigned channel is generally shorter than the original channel which results in a steeper energy gradient in the reach (Case 1). Second, the new channel bank material in the realigned reaches may have a smaller resistance to erosion. As a result of these two problems, the channel may suffer instability by the formation of a headcut from the downstream end and increased bank erosion. The realigned channel may also exhibit a tendency to regain the lost sinuosity and may approach and scour the railroad embankment. To counter these local effects one could design the realignment to maintain the original channel characteristics (length, sinuosity). Another way would be to control the slope by a series of low check dams. In any case, bank protection by riprap, jacks or spurs will be needed. References for Channel Cutoffs Brice, J.C., 1980. "Stability of Relocated Stream Channels," FHWA-RD-80-158, Federal Highway Administration, Washington, D.C. Richardson, E.V., Simons, D.B., and Lagasse, P.F., 2001. "River Engineering for Highway Encroachments – Highways in the River Environment," Report FHWA NHI 01-004, Federal Highway Administration, Hydraulic Design Series No. 6, Washington, D.C. 3.6.4.9 Other Countermeasures Introduction Article 3.6.4.1 through Article 3.6.4.8 contain specific design procedures for a variety of stream instability and bridge scour countermeasures that have been applied successfully on a state or regional basis. Other countermeasures such as retarder structures, longitudinal dikes, bulkheads, and even channel relocations may be used to mitigate scour at bridges or stream bank erosion. Some of these measures are discussed and general guidance is summarized in this section. Hardpoints Hardpoints consist of stone fills spaced along an eroding bank line, protruding only short distances into the channel. A root section extends landward to preclude flanking. The crown elevation of hardpoints used by the USACE at demonstration sites on the Missouri River was generally at the normal water surface elevation at the toe, sloping up at a rate of about 1 ft in 10 ft toward the bank. Hardpoints are most effective along straight or relatively flat convex banks where the streamlines are parallel to the bank lines and velocities are not greater than 10 ft/s within 50 ft of the bank line. Hardpoints may be appropriate for use in long, straight reaches where bank erosion occurs mainly from a wandering thalweg at lower flow rates. They would not be effective in halting or reversing bank erosion in a meander bend unless they were closely spaced, in which case spurs, retarder structures, or bank revetment would probably cost less. Figure 1-3-62 is a perspective of a hardpoint installation. Hardpoints have been used effectively as the first "spur" in a spur field (see Article 3.6.4.4). Retarder Structures Retarder structures are permeable or impermeable devices generally placed parallel to streambanks to reduce velocities and cause deposition near the bank. They are best suited for protecting low banks or the lower portions of streambanks. Retarder structures can be used to protect an existing bank line or to establish a different flow path or alignment. Retards do not require grading of the streambank, and they create an environment which is favorable to the establishment of vegetation. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-136 AREMA Manual for Railway Engineering Natural Waterways Figure 1-3-62. Perspective View of Hardpoint Installation With Section Detail (after Brown) Jacks. Jacks most commonly consist of three linear members fixed together at their midpoints so that each member is perpendicular to the other two. Wires are strung on the members to resist distortion and to collect debris. Cables are used to tie individual jacks together and for anchoring key units to deadmen (Figure 1-3-63). Jacks are effective in protecting banks from erosion only if light debris collects on the structures thereby enhancing their performance in retarding flow. However, heavy debris and ice can damage the structures severely. They are most effective on mild bends and in wide, shallow streams which carry a large sediment load. 1 Where jacks are used to stabilize meandering streams, both lateral and longitudinal rows are often installed to form an area retarder structure rather than a linear structure. Lateral rows of jacks are usually oriented in a downstream direction from 45 to 70. Spacing of the lateral rows of jacks may be 50 to 200 ft depending on the debris and sediment load carried by the stream. A typical jack unit is shown in Figure 3.60 and a typical area installation is shown in Figure 1-3-64. Photographs of jacks and other arrangements that provide similar modus operandi can be found in a paper by Byers. 3 Outflanking of jack installations is a common problem. Adequate transitions should be provided between the upstream bank and the structure, and the jack field should be extended to the overbank area to retard flow velocities and provide additional anchorage. Jacks are not recommended for use in corrosive environments or at locations where they would constitute a hazard to recreational use of the stream. 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-137 Roadway and Ballast Figure 1-3-63. Typical Jack Unit (after Brown) Figure 1-3-64. Retarder Field Schematic (after HDS 6) Fence Retarder Structures. Fence retarder structures provide protection to the lower portions of banks of relatively small streams. Posts may be of wood, steel, or concrete and fencing may be composed of wood planks or wire. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-138 AREMA Manual for Railway Engineering Natural Waterways Scour and the development of flow channels behind linear structures are common causes of failure of longitudinal fences. Scour at the supporting members of the structure can be reduced by placing rock along the fence or the effects of scour can be overcome by driving supporting members to depths below expected scour. Tiebacks can be used to retard velocities between the linear structure and the streambank, thus reducing the ability of the stream to develop flow channels behind the structure. Timber Pile. Timber pile retarder structures may be of a single, double, or triple row of piles with the outside of the upstream row faced with wire mesh or other fencing material. They have been found to be effective at sharp bends in the channel and where flows are directly attacking a bank. They are effective in streams which carry heavy debris and ice loads and where barges or other shipping vessels could damage other countermeasures or a bridge. As with other retarder structures, protection against scour failure is essential. Figure 1-3-65 illustrates a design. Wood Fence. Wood fence retarder structures have been found to provide a more positive action in maintaining an existing flow alignment and to be more effective in preventing lateral erosion at sharp bends than other retarder structures. Figure 1-3-66 is an end view of a typical wood fence design with rock provided to protect against scour. Wire Fence. Wire fence retarder structures may be of linear or area configuration, and linear configurations may be of single or multiple fence rows. Double-row fence retards are sometimes filled with brush to increase the flow retardance. Figure 1-3-67 and Figure 1-3-68 illustrate two types of wire fence retarder structures. Longitudinal Dikes Longitudinal dikes are essentially impermeable linear structures constructed parallel with the streambank or along the desired flow path. They protect the streambank in a bend by moving the flow current away from the bank. Longitudinal dikes may be classified as earth or rock embankment dikes, crib dikes, or rock toe-dikes. 1 3 4 Figure 1-3-65. Timber Pile Bent Retarder Structure (after Brown) © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-139 Roadway and Ballast Figure 1-3-66. Typical Wood Fence Retarder Structure (after Brown) Figure 1-3-67. Light Double Row Wire Fence Retarder Structure (after Brown) © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-140 AREMA Manual for Railway Engineering Natural Waterways 1 3 4 Figure 1-3-68. Heavy Timber-pile and Wire Fence Retarder Structure (after Brown) Earth or Rock Embankments. As the name implies, these dikes are constructed of earth with rock revetment or of rock. They are usually as high or higher than the original bank. Because of their size and cost, they are useful only for large-scale channel realignment projects. Rock Toe-Dikes. Rock toe-dikes are low structures of rock riprap placed along the toe of a channel bank. They are useful where erosion of the toe of the channel bank is the primary cause of the loss of bank material. The USACE has found that longitudinal stone dikes provide the most successful bank stabilization measure studied for channels which are actively degrading and for those having very dynamic beds. Where protection of higher portions of the channel bank is necessary, rock toe-dikes have been used in combination with other measures such as vegetative cover and retarder structures. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-141 Roadway and Ballast Figure 1-3-69 shows the typical placement and sections of rock toe-dikes. The volume of material required is 1.5 to 2 times the volume of material that would be required to armor the sides of the anticipated scour to a thickness of 1.5 times the diameter of the largest stone specified. Rock sizes should be similar to those specified for riprap revetments (see Article 3.6.4.5). Tiebacks are often used with rock toe-dikes to prevent flanking, as illustrated in Figure 1-3-70. Tiebacks should be used if the toe-dike is not constructed at the toe of the channel bank. Rock toe-dikes are useful on channels where it is necessary to maintain as wide a conveyance channel as possible. Where this is not important, spurs could be more economical since scour is a problem only at the end projected into the channel. However, spurs may not be a viable alternative in actively degrading streams (see Article 3.6.4.4). Crib Dikes. Longitudinal crib dikes consist of a linear crib structure filled with rock, straw, brush, automobile tires or other materials. They are usually used to protect low banks or the lower portions of high banks. At sharp bends, high banks would need additional protection against erosion and outflanking of the crib dike. Tiebacks can be used to counter outflanking. Crib dikes are susceptible to undermining, causing loss of material inside the crib, thereby reducing the effectiveness of the dike in retarding flow. Figure 1-3-71 illustrates a crib dike with tiebacks and a rock toe on the stream side to prevent undermining. Bulkheads. Bulkheads are used for purposes of supporting the channel bank and protecting it from erosion. They are generally used as protection for the lower bank and toe, often in combination with other countermeasures that provide protection for higher portions of the bank. Bulkheads are most frequently used at bridge abutments as protection against slumping and undermining at locations where there is insufficient space for the use of other types of bank stabilization measures, and where saturated fill slopes or channel banks cannot otherwise be stabilized. Bulkheads are classified on the basis of construction methods and materials. They may be constructed of concrete, masonry, cribs, sheet metal, piling, reinforced earth, used tires, gabions, or other materials. They must be protected against scour or supported at elevations below anticipated total scour, and where sections of the installation are intermittently above water, provisions must be made for seepage through the wall. Some bulkhead types, such as crib walls and gabions, should be provided with safeguards against leaching of materials from behind the wall. Bulkheads must be designed to resist the forces of overturning, bending and sliding, either by their mass or by structural design. Figure 1-3-72 illustrates anchorage schemes for a sheetpile bulkhead. Because of costs, they should be used as countermeasures against meander migration only where space is not available to construct other types of measures. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-142 AREMA Manual for Railway Engineering Natural Waterways 1 Figure 1-3-69. Typical Longitudinal Rock Toe-dike Geometries (after Brown) 3 4 Figure 1-3-70. Longitudinal Rock Toe-dike Tiebacks (after Brown) © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-143 Roadway and Ballast Figure 1-3-71. Timber Pile, Wire Mesh Crib Dike With Tiebacks (after Brown) Figure 1-3-72. Anchorage Schemes for a Sheetpile Bulkhead (after Brown) © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-144 AREMA Manual for Railway Engineering Natural Waterways References for Other Countermeasures Brown, S.A., 1985. "Streambank Stabilization Measures for Highway Engineers," FHWA/RD-84/100, FHWA, Washington, D.C. Byers, William G. 1962. Stabilization of Canadian River at Canadian, TX, Journal of the Waterways and Harbor Division, Proceedings of ASCE August 1962, WW3, pages 13-26. Lagasse, P.F., Zevenbergen, L.W., Schall, J.D., and Clopper, P.E., 2001. "Bridge Scour and Stream Instability Countermeasures – Experience, Selection, and Design Guidelines," Second Edition, Report FHWA NHI 01-003, Federal Highway Administration, Hydraulic Engineering Circular No. 23, U.S. Department of Transportation, Washington, D.C. Richardson, E.V., Simons, D.B., and Lagasse, P.F., 2001. "River Engineering for Highway Encroachments – Highways in the River Environment," Report FHWA NHI 01-004, Federal Highway Administration, Hydraulic Design Series No. 6, Washington, D.C. SECTION 3.7 MEANS OF PROTECTING ROADBED AND BRIDGES FROM WASHOUTS AND FLOODS 1 3.7.1 GENERAL (1996) Adequate protection against floods and washouts is essential not only for maintenance of dependable service, but also to avoid heavy expenditures to replace damaged facilities and restore operation. 3.7.2 ROADWAY (1996) 3 3.7.2.1 General – Risks and Possible Damage Water overflowing the embankment, either from a direct flow or backwater, frequently results in damage to the roadway. This damage may be as severe as a washout or less apparent in other forms, such as, a loss of the shoulder, a steepening of the embankment, a loss of crib or shoulder ballast, or a softening of the subgrade’s support characteristics. Damage resulting from sloughing and slides are usually more severe as the water recedes from a saturated embankment. Loose, fine-grained, cohesionless soils are more susceptible to sloughing. In general, soil conditions, vegetation, and the rapidity at which the water recedes are primary factors in determining the risk of sloughing. 3.7.2.2 Temporary Protection Measures a. Temporary protection of the roadway section is sometimes necessary, particularly in flood events where immediate action is necessary and time constraints do not permit implementation of a permanent solution. Periodic and close track inspections of flood and washout susceptible areas and identification of high risk locations will be a beneficial first step in determining the appropriate remedial repair. b. Temporary protection of potential overflow slopes and fill sections subject to erosion and sloughing can be provided by placement of an armor of heavy weight material, not easily displaced by floodwaters, such as large-sized stone (riprap) or sandbags. In blanketing the slopes, it is critical that the toe be adequately protected to minimize the risk of base scour and possible embankment failure. Raising the roadbed shoulder with riprap and sandbags can also be a suitable means for temporary relief. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-145 4 Roadway and Ballast 3.7.2.3 Permanent Protection Measures a. In overflow territories, care must be taken to review the adequacy of design, location and construction of existing drainageways and make appropriate corrections if deficiencies are found. Sufficient waterway capacity is essential to minimize heading during floods and, if necessary, provisions should be made for additional relief openings to handle the flow. The impact of runoff from neighboring facilities, existing and proposed, must also be assessed. Input from applicable local, state, or federal authorities should be sought in these preliminary drainage assessments. b. Selection of the optimal permanent protection measure should be done on a site-specific basis and will depend on many factors, including service requirements, severity and extent of the damage potential, embankment soil characteristics, and economic considerations. A subsurface exploration of the area in question, performed during the preliminary stages, can many times generate valuable information and aid in the selection and design process. c. In general, depending upon service requirements, a track raise is the best assurance for reliable operation. Roadbeds subject to severe side erosion can be protected by relocation of the track and/or channel, or construction of revetments as discussed in Article 3.4.5 and Article 3.4.7, respectively. In overflow bottoms where either a channel change, installation of additional openings, or a track raise or relocation do not afford sufficient relief, consideration should be given to facing the downstream side of the roadbed at least at critical locations with riprap or other suitable means of protection. Covering erosion-susceptible slopes with a thick vegetative cover can furthermore provide protection by impeding surface erosion. d. On light traffic density lines where the aforementioned extensive measures cannot be economically justified, consideration might be given to anchoring the track to the roadbed, at designated locations throughout the overflow area, utilizing cable tied to rail, timber pile, or screw anchors driven in the roadbed. Under these conditions use of a heavy course ballast tends to reduce the incidence of ballast displacement. When using this last method of protection, the railroad is accepting the risk of traffic disruption due to flooding and washouts. 3.7.3 BRIDGES (1996) 3.7.3.1 General – Risks and Possible Damage Protection against flood damage for structures calls for resourcefulness during the immediate flooding threat, as well as during the implementation of permanent protection measures. Temporary measures should be given consideration to prevent both minor and major damage. Minor damage can be categorized as scour on the shoulders or behind the abutments, debris hung up in the waterway opening, overtopping, and various other damage that can be immediately detected and repaired. Major damage are items such as contamination of ballast decks and roadbed; scouring around piling, piers, foundations, and backwalls; channel changes resulting in silting or bypassing the structure; culvert piping or joint separation; etc. 3.7.3.2 Temporary Protection Measures The need for temporary protection should be considered not only prior to and during floods, but also when the structure is under construction. Temporary measures to consider during or immediately preceding a flood include, identification of high-risk areas, frequent inspection, remove or pass debris through the structure to avoid accumulation, and the placement of riprap or sandbags. The following are temporary measures to be considered when the structure is in the design or construction stage; all the measures considered previously, and others such as fence jetties, rock jetties, and channel cutoffs. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-146 AREMA Manual for Railway Engineering Natural Waterways 3.7.3.3 Permanent Protection Measures Permanent protection measures require that sound engineering principles be employed to protect the structure from flood damage and allow its continued function as designed. Bridges and culverts must be designed with sufficient waterway opening to handle the design storm. In addition, both structures must be designed with an adequate opening to pass the anticipated debris. This also requires occasional re-evaluation as the drainage area or other conditions change. Some of the measures detailed in various articles in Section 3.4, Basic Concepts and Definitons of Scour, may need to be incorporated in the structures protection plan. Permanent protection might also include underwater or other inspections of potential problem areas. SECTION 3.8 CONSTRUCTION AND PROTECTION OF ROADBED ACROSS RESERVOIR AREAS1 3.8.1 GENERAL (1978) a. The construction and protection of roadbed across reservoir areas present many problems that are not encountered in normal roadbed construction. Analysis of these problems can best be made by subdividing the subject into three sections, as follows: • Determination of Wave Heights 1 • Construction of Embankment and Roadbed • Construction of Embankment Protection b. The term “reservoir area” as used in this report also includes lakes, natural and artificial river pools, and other inland waters on which waves may be generated. 3 3.8.2 DETERMINATION OF WAVE HEIGHTS (1978) a. Knowledge relating to wind velocities over land and over water, and wave heights on inland reservoirs, has increased in recent years as a result of studies made by the Coastal Research Center (formerly known as the Beach Erosion Board), and by the Corps of Engineers at Fort Peck Reservoir in northeast Montana, Denison Reservoir on the Oklahoma-Texas state line, and Lake Okeechobee in Southern Florida. b. These studies resulted in the publication of Technical Memorandum No. 132, “Waves in Inland Reservoirs” (Reference 4) by the Beach Erosion Board, essentially the same information having appeared in ASCE Proceedings Paper No. 3138 (May 1962), corrected May 1963. c. The methods subsequently described are adapted from Technical Memorandum No. 132, and are adequate for ordinary wave problems. For more extensive or complicated situations, the designer should refer to Technical Memorandum No. 132, or to Technical Report No. 4, “Shore Protection Planning and Design” (Reference 5) by the Beach Erosion Board, or to other references listed in these publications. d. Elements affecting the determination of wave heights may be listed as follows. 1 References, Vol. 56, 1955, pp. 706, 1118; Vol. 57, 1956, pp. 649, 1080; Vol. 63, 1962, pp. 578, 749; Vol. 66, 1965, pp. 523, 746; Vol. 78, 1977, p. 124. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-147 4 Roadway and Ballast 3.8.2.1 Effective Fetch (F) a. Fetch, or the distance over which the wind blows, was originally designated as the greatest straight-line distance across open water. Subsequent studies have shown that the shape of an open-water area affects the effective fetch. b. For a given size and shape of water area, effective fetch is determined by laying out seven radials at 6 degrees intervals on each side of a central line through the point under study, extending them to their point of intersection with the shore line. The scaled component of each radial’s projection on the central radial is then multiplied by the cosine of its angle with the central radial. The sum of these values divided by the sum of the cosines determines the effective fetch (F) for that location. An example of this calculation is shown in Figure 1-3-75. 3.8.2.2 Wind Velocity (U) a. Wind velocities over water are higher than over land, and although individual observed values may vary considerably, average values for this relationship have been observed as shown in Table 1-3-20. Table 1-3-20. Wind Relationship – Land to Water Fetch in Miles U water Wind ratio --------------------U land 0.5 1.08 1 1.13 2 1.21 4 1.28 6 and over 1.31 b. Thus, a wind having a velocity of 40 mph over land could be expected to attain a velocity of 40 1.28, or 51 mph over water if the effective fetch were 4 miles. 3.8.2.3 Minimum Wind Duration (ta) With wind velocity assumed to be constant over a particular fetch, the height of waves being generated will progressively increase with time up to a maximum value for that velocity. The minimum wind duration in minutes for producing this maximum wave can be determined from the dashed lines in Figure 1-3-73, given the wind velocity in miles per hour and the effective fetch in miles. 3.8.2.4 Significant Wave Height (Hs) Although successive waves in a group will vary in height, the significant wave height is defined as the average of the highest one-third of the waves being generated, measured from trough to crest, and is determined from the solid diagonal lines in Figure 1-3-73. Since wind-generated waves on a large body of water are not uniform in height, the significant wave height thus determined will be exceeded approximately 13% of the time. 3.8.2.5 Specific, or Design, Wave Height (Ho) a. Wave studies have shown that wind-generated waves are not uniform in height, but consist of groups of waves with varying heights. Studies of inland reservoirs show the following relationship between the significant wave height (Hs) which is exceeded 13% of the time, and a selected specific wave height (Ho) exceeded less frequently (Table 1-3-21). b. Having determined the significant wave height from Figure 1-3-73, a design wave of acceptable frequency of occurrence is computed by multiplying Hs by the corresponding ratio value in Table 1-3-21. A ratio of 1.87 is frequently used for the so-called maximum wave, but over extended periods of observation, individual waves may even exceed this value. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-148 AREMA Manual for Railway Engineering Natural Waterways 1 Figure 1-3-73. Wave Heights and Minimum Wind Durations 3 Table 1-3-21. Wave Height Distributions Ratio of Specific Wave Height Ho to Significant Wave Height Hs (Ho / Hs) (1) Percent of Waves Exceeding Specific Wave Height Ho (2) 1.00 13 1.07 10 1.27 4 1.40 2 1.60 1 1.67 0.4 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-149 Roadway and Ballast 3.8.2.6 Wave Period (T) The significant wave period represents the average interval in seconds between successive waves, and is determined from Figure 1-3-74. The resulting wave period is also applicable to the higher waves in the group. 3.8.2.7 Wave Length (L) a. The wave length (L) is measured from crest to crest of waves in feet, and is equal to 5.12 T2. However, wave heights and other characteristics are limited by the depth of water in which they are generated if that depth is less than approximately one-half the wave length. Observations at Lake Okeechobee (Reference 32) indicated that waves were limited to a maximum significant wave height of approximately 0.6 of the average depth of water in the generating area, regardless of duration and velocity of wind. b. For determining the characteristics of shallow-water-generated waves, reference may be made to the previously mentioned Technical Memorandum No. 132, or Technical Report No. 4. Figure 1-3-74. Wave Periods © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-150 AREMA Manual for Railway Engineering Natural Waterways 3.8.2.8 Set-up, or Wind Tide (S) a. An enclosed body of water over which a wind is blowing tends to pile up at higher elevations at the leeward end, and on long fetches this set-up may assume importance in the design of bank protection. The increase in water level above the still-water elevation that would prevail without wind action is determined by the formula: 2 U F S = -----------------1400D where: S = set-up in feet U = velocity of the wind in miles per hour F = fetch in statute miles D = average depth of the body of water in feet b. Fetch distance used here differs from effective fetch (F) previously described in that it may be of a curved or sweeping character, and need not move in a straight line. It can also be greater in length than the effective fetch (see Figure 1-3-75). 1 3 4 Figure 1-3-75. Fetch Example Calculation © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-151 Roadway and Ballast 3.8.2.9 Wave Run-up (R) On readying a fill a wave will run up the slope to an elevation largely dependent on the angle of the slope, the roughness of the embankment, and the steepness of tide wave (Ho/Lo). From Figure 1-3-76, relative run-up on smooth or average riprap covered slopes can be determined where the embankment slope and steepness of design wave are known. Run-up (R) in feet is secured by multiplying the relative run-up thus found by the design wave height (Ho), and total run-up will then be the sum of run-up (R) and set-up (S). Figure 1-3-76. Wave Run-up Ratios © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-152 AREMA Manual for Railway Engineering Natural Waterways 3.8.2.10 Summary For a sample computation for determining wave height and protection needs see Table 1-3-22 and Figure 1-375. Table 1-3-22. Sample Computation for Determining Wave Height and Protection Needs (See Figure 1-3-75) Description 1. Effective fetch (F) Amount 1.42 miles 2. Average wind velocity over land 40 mph 3. Average wind velocity over water (U), = 40 1.21 from Table 1-3-20 48 mph 4. Minimum duration (td) to produce computed wave, from Figure 1-3-73 23 min 5. Significant wave height (Hs), from Figure 1-3-73 2.6 ft 6. Design wave height (Ho), exceeded by only 0.4% of the waves, = Hs + 1.67 from Table 1-3-21 4.3 ft 7. Wave period (T) for significant and design waves, from Figure 1-3-74 8. Wave length (Lo) for design wave = 5.12 T2 9. Wave steepness (Ho/Lo) = 4.3/46.1 3.0 sec 46.1 ft 0.093 2 U Fs - , where wind tide fetch (Fs) is 6.24 miles (Figure 1-3-75), and average 10. Set-up (S) = ----------------1400 D depth of lake is 30 ft 0.34 ft 11. Relative run-up ratio (R/Ho) for riprap on 2.5:1 slope, and HoLo = 0.093, using Figure 1-3-76 0.94 12. Wave run-up, (R), (line 6 line 11) 13. Total run-up, (line 10 + line 12) Weight of rock protection, from Article 3.8.4.2, where: S = 2.6 for limestone H = 4.3, design wave height cot a = 2.5 for 2.5:1 slope then: Wavg Wmax Wmin Minimum Thickness 4.0 4.3 ft 3 162 lb 648 lb 20 lb 18 in 3.8.3 CONSTRUCTION OF EMBANKMENT AND ROADBED (1978) a. The embankment should be constructed in accordance with Part 1, Roadbed, except as modified in conformance with the following: b. That portion of the embankment which will be submerged should have side slopes not steeper than 3 to 1, and no material should be used in the embankment which has a liquid limit in excess of 60 as determined in accordance with ASTM Designation D 423-61T, Standard Method of Test for Liquid Limit of Soils. Width of roadbed, side slopes, prepared ballast and sub-ballast should be in accordance with the standards of the railroad company. Factors not encountered in ordinary roadbed construction that should receive consideration include probable maximum water-surface elevation, frequency of occurrence and duration of embankment submergence, possible head on the embankment (water surface on one side higher in elevation), and drawdown effect due to the rapid release of stored water. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1 1-3-153 4 Roadway and Ballast c. The probable maximum water surface elevation, together with the design wave height, wind tide and wave run-up effects will govern the elevation at which the roadbed should be constructed. In special cases the increased headwater elevation due to inflowing water may also be significant. d. Frequency and duration of embankment submergence is important in determining the suitability of available embankment material and recommended slopes. An embankment that is stable under ordinary conditions may not be stable when saturated because of long submergence. e. The permeability of the soil to be used in the embankment should be considered in connection with the probable maximum rate of drawdown in the case of reservoirs. Embankments composed of impervious materials that are stable when dry, or even when saturated, may fail if the water surface is lowered rapidly while the embankment is saturated. Pervious free-draining soils are not as susceptible to failure from this cause as are impervious soils. 3.8.4 CONSTRUCTION OF EMBANKMENT PROTECTION (1978) 3.8.4.1 General Experience has shown that in the majority of cases, dumped riprap furnishes the best type of protection at the lowest ultimate cost. Its effectiveness depends on the quality of the rock and its weight or size, thickness of the layer, shape of the individual stones, slope of the embankment, and stability of tile base or filter on which it is placed. Usually, the availability of riprap sources determines to some extent the quality and size of stone used for slope protection. 3.8.4.2 Weight and Thickness of Riprap a. Formulas for rock protection of slopes have, until recent years, become more applicable to costal installations. Requirements for inland bodies of water have been found to require somewhat different standards of design. One extremely useful set of formulas appears in the Corps of Engineers’ Manual, EM 1110-2-2300 (1 April 1959), and is substantially as follows: 2 62.4aS H o W avg = ------------------------------------------------------3 1.82 S – 1 cot a W max = 4 ¥ W avg W avg W max = ------------8' Minimum Thickness in Inches = 18 3 W avg -----------------62.4 S where: W = weight of individual stones in pounds S = specific gravity of the rock Ho = design wave height in feet a = the angle of slope with the horizontal b. Gradation of weights of stone should fall within the following classifications: At least 45% shall be greater than Wavg with not more than 10% greater than Wmax or 10% less than Wmin. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-154 AREMA Manual for Railway Engineering Natural Waterways c. It should be noted that riprap selected by the use of these formulas is suitable for protecting embankments against wave action in normal circumstances. Special consideration should be given to specific needs for protection of foundations from scour, or at locations where riprap may be displaced by ice action. d. All stone for riprap shall be preferably of angular and irregular shape, and of a quality that will reasonably withstand the action of water, frost, or other weathering. 3.8.4.3 Minimum Requirements a. The protective covering should extend from the natural ground surface at the toe of slope to an elevation at least 2.0 feet above the height of total run-up as determined in Article 3.8.2.9, or 4.0 feet above stillwater elevation, whichever is greater. Where the natural ground does not provide adequate support, or where scour is possible, riprap should be extended below the toe of slope by trenching to the required depth. b. The thickness of riprap cover should satisfy design requirements of Article 3.8.4.2, but should not be less than 18 inches thick. 3.8.4.4 Filter Blanket a. A bedding layer or filter blanket should be provided underneath riprap protection when the compacted material of the underlying embankment consists of silt or fine sand. In this case there is danger of the fill material being washed out through voids in the riprap by wave action which can result in undermining of the cover material. b. The filter blanket, composed of gravel (preferably crushed), crushed rock or slag, should be not less than 6 inches and not more than 12 inches in thickness, and should be placed on the embankment slope to form a backing for the riprap protection, and should be reasonably well graded within the limits found in Table 1-3-23. 1 3 Table 1-3-23. Filter Blanket Limits Sieve Size Percent by Weight Passing 3 inch 100 1-1/2 inch No. 40 4 40-60 0-5 3.8.4.5 Littoral Currents and Refraction Littoral current, the result of waves breaking at an angle to the shoreline, and refraction, the process by which the direction of a wave moving in shallow water at an angle to bottom contours is changed, are primarily the concern of designers of coastal shore-protection structures, and are not covered here. Reference is made to the Beads Erosion Board’s Technical Report No. 4, “Shore Protection Planning and Design,” for detailed information on these subjects. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-155 Roadway and Ballast SECTION 3.9 GLOSSARY The following terms are for general use in Part 3. Specialized terms appear in individual paragraphs. Refer to the Glossary located at the end of the chapter for definitions. Abrasion Aggradation Alluvial Channel Alluvial Fan Alluvial Stream Alluvium Alternating Bars Anabranch Anabranched Stream Anastomosing Stream Angle of Repose Annual Flood Antecedent Moisture Condition Apron Apron, Launching Areal Precipitation Distribution Armor (Armoring) Articulated Concrete Mattress Artificial Obstruction Average Velocity Avulsion Backcurrent Backfill Backwater Backwater Area Bank Bank, Left (Right) Bank Protection Bank Revetment Bankfull Discharge Bar Base Floodplain Bed Bed Form Bed Layer Bed Load Bed Load Discharge (or Bed Load) Bed Material Bed Sediment Discharge Bed Shear (Tractive Force) Bed Slope Bedding Layer Bedrock Blanket Boulder Braid Braided Stream Bridge Opening Bridge Waterway Bulk Density Bulkhead Bulking Catchment Causeway Caving Cellular-block Mattress Channel Channel Cut-off Channel Diversion Channel Pattern Channel Process Channelization Check Dam Choking (of Flow) Clay (Mineral) Clay Plug Clear-Water Scour Cobble Cohesionless Soil Concrete Revetment Confluence Constriction Contact Load Contraction Contraction Scour Coriolis Force Countermeasure Crib © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-156 AREMA Manual for Railway Engineering Natural Waterways Crib Dike Critical Shear Stress Cross Section Crossing Culvert Current Current Meter Curve Number Method Cut Bank Cutoff Cutoff Wall Daily Discharge Debris Degradation Degradation (Bed) Depth of Scour Design Flow (Design Flood) Dike Dike (Groin, Spur, Jetty) Dikes, Jetties, Groins Discharge (Q) Dominant Discharge Drainage Basin Area (A) Drainage Structure Drawdown Effect Drift Eddy Current Effective Fetch (F) Embankment Entrenched Stream Ephemeral Stream Equilibrium Scour Erosion Erosion Control Matting Exceedance Probability Fabric Mattress Fall Velocity Fascine Fence Jetty Fetch Fetch Length Fill Slope Filter Filter Blanket Filter Fabric (Cloth) Fine Sediment Load Flanking Flashy Stream Flood-frequency Curve Floodplain Floods Flow-control Structure Flow Hazard Flow Slide Fluvial Geomorphology Fluvial System Foreshore Freeboard Froude Number Gabions General Scour Geomorphology/Morphology Grade-control Structure (Sill, Check Dam) Graded Stream Gravel Groin Grout Guide Bank Hardpoint Headcutting Heading Helical Flow Hydraulic Capacity Hydraulic Model Hydraulic Problem Hydraulic Radius Hydraulic Structures Hydraulics Hydrograph Hydrology Icing Imbricated Impermeable Impervious Incised Reach Incised Stream 1 3 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-157 Roadway and Ballast Infiltration Interface Invert Island Jack Jack Field Jetty Lateral Erosion Launching Laursen Scour Design Leeward Levee Liquid Limit (LL) Littoral Current Live-bed Scour Load (or Sediment Load) Local Scour Log Pearson Type III Distribution Longitudinal Profile Lower Bank Mathematical Model Mattress Meander or Full Meander Meander Amplitude Meander Belt Meander Length Meander Loop Meander Radius of Curvature Meander Ratio Meander Scrolls Meander Width Meandering Stream Median Diameter Mid-channel Bar Middle Bank Migration Minimum Wind Duration (ta) Mud Natural Levee Neville Sediment-Transport Scour Design Nominal Diameter Nonalluvial Channel Normal Stage Overbank flow Overtopping/Overflowing Oxbow Pavement Paving Peaked Stone Dike Perennial Stream Permeable Phreatic Line Pile Pile Dike Pilot Channel Piping Point Bar Poised Stream Probable Maximum Flood Propeller Backwash Quarry-run Stone Railbank Protection Rainfall Intensity (i) Rapid Drawdown Rational Method Reach Recurrence Interval Refraction Regime Regime Change Regime Channel Regime Formula Reinforced-earth Bulkhead Reinforced Revetment Relief Bridge Retard (Retarder Structure) Return Period (T) Revetment Riffle Riparian Riprap River Training Rock Jetty Dike Rock-and-wire Mattress Roughness Coefficient Rubble © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-158 AREMA Manual for Railway Engineering Natural Waterways Runoff Runoff Coefficient (c) Sack Revetment Saltation Load Sand Scour Sediment or Fluvial Sediment Sediment Concentration Sediment Deposition Sediment Discharge Sediment Load Sediment-Transport Scour Sediment Yield Seepage Shear Stress Sheet Pile Shoal Significant Wave Height (HS) Sill Silt Silting Sinuosity Slope (of Channel or Stream) Slope Protection Sloughing Slope-area Method Slump Soil-cement Sorting Specific Wave Height (HO) Spill-through Abutment Spread Footing Spur Spur Dike Stability Stable Channel Stage Stone Riprap Storm Duration (t) Stream Streambank Erosion Streambank Failure Streambank Protection Sub-bed Material Subcritical, Supercritical Flow Surface Runoff Suspended Sediment Discharge Temporal Precipitation Distribution Tetrahedron Tetrapod Thalweg Tieback Timber or Brush Mattress Timber Pike Dike Time of Concentration (tc) Toe of Bank Toe Protection Total Scour Total Sediment Load Tractive Force Trench-fill Revetment Turbulence Ultimate Scour Ultimate Total Abstraction (S) Undermining Uniform Flow Unit Discharge Unit Shear Force (Shear Stress) Unsteady Flow Upper Bank Velocity Velocity (V) - Water Velocity (U) - Wind Vertical Abutment Vortex Wandering Channel Wandering Thalweg Wash Load Washout Watershed Waterway Opening Width (Area) Wave Length (L) Wave Period (T) Wave Run-up (R) Weephole Wind Tide (S) 1 3 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-3-159 Roadway and Ballast Windrow Revetment Wire Mesh © 2010, American Railway Engineering and Maintenance-of-Way Association 1-3-160 AREMA Manual for Railway Engineering 1 Part 4 Culverts1 — 2006 — TABLE OF CONTENTS Section/Article Description Page 4.1 Location and Type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.1 Waterway Required (1995) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.2 Span Required (1995) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.3 Character of Hydraulic Bedload (Abrasive, Corrosive, Etc.) (1995) . . . . . . . . . . . . . . . . . . 4.1.4 Topographic Conditions Determining Angle, Gradient, and Length of Structure (1987) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.5 Foundation Conditions (1987) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.6 Height and Character of Embankment (1987) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.7 Loading, Live and Dead (1984) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.8 Economics of Various T ypes (1984) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-7 1-4-7 1-4-8 1-4-8 1-4-9 4.2 Specifications for Placement of Reinforced Concrete Culvert Pipe. . . . . . . . . . . . . . . 1-4-9 4.3 Specifications for Prefabricated Corrugated Steel Pipe and Pipe-arches for Culverts, Storm Drains, and Underdrains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.1 General (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.2 Material (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.3 Fabrication (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.4 Coupling Bands (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.5 Shape (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.6 Workmanship (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.7 Mill or Shop Inspection (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.8 Field Inspection and Acceptance (1989). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-10 1-4-10 1-4-10 1-4-10 1-4-13 1-4-14 1-4-16 1-4-16 1-4-17 4.4 Specifications for Coated Corrugated Steel Pipe and Arches . . . . . . . . . . . . . . . . . . . . 4.4.1 Specification for Bituminous Coated Galvanized Steel Pipe and Pipe Arches (1989). . . . 4.4.2 Specification for Polymeric Coated Corrugated Galvanized Steel Pipe or Pipe Arches (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1-4-6 1-4-6 1-4-6 1-4-6 1-4-17 1-4-17 1-4-17 References, Vol. 40, 1939, pp. 520, 729; Vol. 51, 1950, pp. 708, 839; Vol. 54, 1953, pp. 108, 1385; Vol. 62, 1961, pp. 678, 936; Vol. 85, 1984, p. 5; Vol. 89, 1988, p. 40; Vol. 90, 1989, p. 34; Vol. 93, 1992, pp. 34, 39; Vol. 94, 1994, p. 30; Vol. 96, p. 20. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-1 1 3 Roadway and Ballast TABLE OF CONTENTS (CONT) Section/Article Description Page 4.5 Standard Specification for Corrugated Aluminum Alloy Pipe. . . . . . . . . . . . . . . . . . . . 4.5.1 General (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.2 Material (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.3 Fabrication (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.4 Coupling Bands – Class I and Class II (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.5 Shape – Class I and Class II (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-17 1-4-17 1-4-18 1-4-20 1-4-22 1-4-23 4.6 Specifications for Corrugated Structural Steel Plate Pipe, Pipe-arches, and Arches 4.6.1 General (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6.2 Material (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6.3 Fabrication (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-24 1-4-24 1-4-24 1-4-26 4.7 Specifications for Corrugated Structural Aluminum Alloy Plate Pipe, Pipe-arches, and Arches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7.1 General (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7.2 Material (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7.3 Fabrication (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-26 1-4-26 1-4-26 1-4-28 4.8 Hydraulics of Culverts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8.1 Introduction (1989). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8.2 Design Method (1989). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8.3 Flow Conditions (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8.4 Hydraulic Computations (1989). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-29 1-4-29 1-4-29 1-4-30 1-4-34 4.9 Design Criteria for Corrugated Metal Pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9.1 Criteria (1994). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9.2 Formulas (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9.3 Loads (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9.4 Pipe Culvert Design Properties (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9.5 Minimum and Maximum Height of Cover in Feet (1989) . . . . . . . . . . . . . . . . . . . . . . . . . 4.9.6 Pipe Arches (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-56 1-4-56 1-4-56 1-4-58 1-4-58 1-4-60 1-4-63 4.10 Design Criteria for Structural Plate Pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.10.1 Criteria Formulas (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.10.2 Seam Strength of Structural Plate Pipes (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.10.3 Minimum and Maximum Height of Cover in Feet (1989) . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-65 1-4-65 1-4-65 1-4-66 4.11 Culvert End Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.11.1 Introduction (1992). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.11.2 Headwalls (1989) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.11.3 Wingwalls (1995) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.11.4 Inverts and Aprons (1995) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-68 1-4-68 1-4-68 1-4-69 1-4-70 4.12 Assembly and Installation of Pipe Culverts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.12.1 General (1995) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.12.2 Alignment (1995) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.12.3 Construction Methods (1995). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.12.4 Preparation of Foundation (1995) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.12.5 Handling and Unloading (1995). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.12.6 Assembly (1995) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-70 1-4-70 1-4-71 1-4-71 1-4-71 1-4-71 1-4-72 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-2 AREMA Manual for Railway Engineering Culverts TABLE OF CONTENTS (CONT) Section/Article 4.12.7 4.12.8 4.12.9 4.12.10 4.12.11 Description Page Backfill (1995) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multiple Installations (1995) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . End Treatment (1995). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Protection of Pipe Culvert from Construction Loads (1995) . . . . . . . . . . . . . . . . . . . . . . . Safety Provisions (1995) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-72 1-4-74 1-4-74 1-4-74 1-4-75 4.13 Earth Boring and Jacking Culvert Pipe through Fills . . . . . . . . . . . . . . . . . . . . . . . . . . 4.13.1 General (1995) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.13.2 Type of Pipe Suitable for Jacking (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.13.3 Size and Length of Pipe (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.13.4 Precautions in Unstable Soils (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.13.5 Protection of Pipe Against Percolation, Piping and Scour (1992) . . . . . . . . . . . . . . . . . . . 4.13.6 Safety (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-75 1-4-75 1-4-76 1-4-76 1-4-76 1-4-77 1-4-77 4.14 Culvert Rehabilitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.14.1 General (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.14.2 Survey of Existing Structures (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.14.3 Methods of Rehabilitation (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.14.4 Localized Repairs (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.14.5 Relining Materials (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.14.6 In Place Installation of Concrete Invert (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-77 1-4-77 1-4-77 1-4-78 1-4-78 1-4-79 1-4-81 4.15 Specification for Steel Tunnel Liner Plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.15.1 General (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.15.2 Material (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.15.3 Fabrication (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.15.4 Coatings (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.15.5 Design (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-82 1-4-82 1-4-83 1-4-83 1-4-84 1-4-84 4.16 Construction of Tunnel Using Steel Tunnel Liner Plates. . . . . . . . . . . . . . . . . . . . . . . . 4.16.1 Scope (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.16.2 Description (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.16.3 Installation (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.16.4 Measurement (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.16.5 Payment (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-90 1-4-90 1-4-90 1-4-90 1-4-90 1-4-90 4.17 Culvert Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.17.1 Introduction (2001) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.17.2 Definition of a Culvert (2001) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.17.3 Key Differences From Bridges and Other Structures (2001) . . . . . . . . . . . . . . . . . . . . . . . 4.17.4 Safety (2001) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.17.5 Inventory, Assessment of Existing Conditions, and Frequency of Inspection (2001) . . . . 4.17.6 Physical Condition Assessment (2001). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.17.7 Evaluation/Recommended Action (2001) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.17.8 Inspection Follow-up (2001) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-91 1-4-91 1-4-91 1-4-91 1-4-92 1-4-93 1-4-94 1-4-97 1-4-97 4.18 Perforated Pipe Drains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.18.1 General (2006) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.18.2 Applications (2006) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-100 1-4-100 1-4-100 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-3 1 3 4 Roadway and Ballast TABLE OF CONTENTS (CONT) Section/Article 4.18.3 4.18.4 4.18.5 4.18.6 4.18.7 4.18.8 4.18.9 4.18.10 Description Page Materials (2006) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Related Filter Materials (2006) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hydraulic Design (2006). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Structural Design (2006) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Construction Requirements (2006) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Inspection and Acceptance (2006) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Operation and Maintenance (2006) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Safety Provisions (2006). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-100 1-4-101 1-4-101 1-4-102 1-4-102 1-4-104 1-4-104 1-4-104 LIST OF FIGURES Figure 1-4-1 1-4-2 1-4-3 1-4-4 1-4-5 1-4-6 1-4-7 1-4-8 1-4-9 1-4-10 1-4-11 1-4-12 1-4-13 1-4-14 1-4-15 1-4-16 1-4-17 1-4-18 1-4-19 1-4-20 1-4-21 1-4-22 1-4-23 1-4-24 Description Page Inlet Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Outlet Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Relationship of Headwater to High Tailwater and Other Terms in EQ 4-1 . . . . . . . . . . . . . . . Low Tailwater in Relation to Terms of the Flow Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . Difference Between Energy Grade Line and Hydraulic Grade Line . . . . . . . . . . . . . . . . . . . . . Inlet Control – Headwater Depths for Corrugated Metal Pipe Culverts . . . . . . . . . . . . . . . . . . Inlet Control – Headwater Depths for Corrugated Metal Pipe-arch Culverts. . . . . . . . . . . . . . Inlet Control – Headwater Depths for Structural Plate Pipe-arch Culverts with 18-inch Radius Corner Plate for Three Types of Inlet (Reference 22) . . . . . . . . . . . . . . . . . . . . . . . Inlet Control – Headwater Depths for Structural Plate Pipe-arch Culverts with 31-inch Radius Corner Plate for Three Types of Inlet (Reference 22) . . . . . . . . . . . . . . . . . . . . . . . Inlet Control – Headwater Depths for Concrete Pipe Culverts for Three Types of Inlet (Reference 22) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Inlet Control – Headwater Depths for Oval Concrete with Long Axis Horizontal for Three Types of Inlet (Reference 22) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Inlet Control – Headwater Depths for Oval Concrete Pipe Culverts with Long Axis Vertical for Three Types of Inlet (Reference 22) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Outlet Control – Head for Corrugated Metal Pipe Culvert with Submerged Outlet and Culvert Flowing Full (See Note Under Sketch at Top) (Reference 22). . . . . . . . . . . . . . . . Outlet Control – Head for Corrugated Metal Pipe-arch Culvert with Submerged Outlet and Flowing Full (Reference 22). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Outlet Control – Head for Structural Plate Pipe Culvert with Submerged Outlet and Flowing Full (Reference 22) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Outlet Control – Head for Structural Plate Pipe-arch Culvert with 18-Inch Corner Radius with Submerged Outlet and Flowing Full (Reference 22) . . . . . . . . . . . . . . . . . . . . . . . Outlet Control – Head for Concrete Pipe Culverts with Submerged Outlet and Flowing Full (Reference 22) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Outlet Control – Head for Oval Concrete Pipe Culverts with Long Axis Horizontal or Vertical Submerged Outlet and Flowing Full (Reference 22). . . . . . . . . . . . . . . . . . . . . . . . . . . Hydraulic Elements for Circular Corrugated Steel Pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hydraulic Properties of Corrugated Steel and Structural Plate Pipe-arches . . . . . . . . . . . . . . Comparison of Waterway Cross-sectional Areas at Equal Depths of Flow in Circular Pipe and Pipe-arch. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Proper Bedding and Haunch Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Minimum Permissible Spacings for Multiple Installations . . . . . . . . . . . . . . . . . . . . . . . . . . . . Using Warped Fill to Balance Loads Across Ends of Culverts . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-30 1-4-31 1-4-33 1-4-33 1-4-33 1-4-36 1-4-37 1-4-38 1-4-39 1-4-40 1-4-41 1-4-42 1-4-44 1-4-45 1-4-46 1-4-47 1-4-48 1-4-49 1-4-50 1-4-52 1-4-55 1-4-73 1-4-74 1-4-75 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-4 AREMA Manual for Railway Engineering Culverts LIST OF FIGURES (CONT) Figure 1-4-25 1-4-26 1-4-27 1-4-28 1-4-29 Description CMP Liner Pipe Installation Showing Guide Rails, Grout Plugs and Adjusting Rods . . . . . . . Example of New Invert in CMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagram for Coefficient Cd for Tunnels in Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Culvert Inspection Form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical Underdrain Detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 1-4-80 1-4-82 1-4-87 1-4-98 1-4-102 LIST OF TABLES Table 1-4-1 1-4-2 1-4-3 1-4-4 1-4-5 1-4-6 1-4-7 1-4-8 1-4-9 1-4-10 1-4-11 1-4-12 1-4-13 1-4-14 1-4-15 1-4-16 1-4-17 1-4-18 1-4-19 1-4-20 1-4-21 1-4-22 1-4-23 1-4-24 1-4-25 1-4-26 1-4-27 1-4-28 1-4-29 1-4-30 1-4-31 1-4-32 1-4-33 1-4-34 1-4-35 1-4-36 1-4-37 Description Page Corrugations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-11 Perforations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-11 Pipe Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-12 Riveted Seams. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-13 Pipe Arch Specification Requirements Pipe Arches – 2-2/3 1/2 Corrugations (See Note 3) 1-4-15 Pipe Arch Specification Requirements Pipe Arches – 3 1 and 5 1Corrugations (See Note 2) . . 1-4-15 Gage or Decimal Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-18 Chemical Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-19 Mechanical Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-19 Dimensions of Corrugations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-21 Minimum Rivet Diameter (See Note 3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-21 Pipe Sheet Thickness to Lock Seam Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-22 Flat Sheet or Plate, Bolts, Nuts, and Extrusion Physical Properties . . . . . . . . . . . . . . . . . . . . . 1-4-27 Entrance Loss Coefficients for Corrugated Metal Pipe or Pipe Arch (Reference 22) . . . . . . . . 1-4-31 Values of Coefficient of Roughness (n) for Standard Corrugated Metal Pipe (Manning’s Formula) (Reference 1). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-35 Values of n for Structural Plate Pipe for 62 Corrugations (Manning’s Formula) (Reference 25) 1-4-35 Length Adjustment for Improved Hydraulics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-44 Length Adjustment for Improved Hydraulics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-46 Length Adjustments for Improved Hydraulics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-47 Full Flow Data for Round Pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-51 Full Flow Data for Corrugated Steel Pipe-arches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-52 Full Flow Data for Structural Plate Pipe-arches – Corrugations 6 2 . . . . . . . . . . . . . . . . . . 1-4-53 Full Flow Data for Corrugated Steel Pipe-arches – Corrugations 6 2 . . . . . . . . . . . . . . . . . 1-4-54 Live Loads for Cooper E-80 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-58 Gage vs Metal Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-58 Metal Mechanical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-58 Minimum Longitudinal Seam Strength in Kips per Foot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-59 Steel and Aluminum Corrugated Pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-59 Steel Round Corrugated Pipe Minimum and Maximum Height of Cover in Feet . . . . . . . . . . . 1-4-61 Aluminum Round Corrugated Pipe Minimum and Maximum Height of Cover in Feet . . . . . . 1-4-62 Typical Allowable Bearing Pressures (See Note 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-63 Steel and Aluminum Arch Pipes Minimum Thickness of Metal (Gage) . . . . . . . . . . . . . . . . . . . 1-4-64 Steel and Aluminum Structural Plate Pipes in Kips per Foot all Bolts to be 3/4 inch in Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-65 Steel and Aluminum Structural Plate Pipes Section Properties. . . . . . . . . . . . . . . . . . . . . . . . . 1-4-65 Steel Round Structural Plate Pipe Minimum and Maximum Height of Cover (ft) . . . . . . . . . . 1-4-66 Aluminum Round Structural Plate Pipe Minimum and Maximum Height of Cover (ft) . . . . . 1-4-67 Aluminum Round Structural Plate Pipe Minimum and Maximum Height of Cover (ft) . . . . . 1-4-67 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-5 1 3 4 Roadway and Ballast LIST OF TABLES (CONT) Table Description Page 1-4-38 Effective Sectional Properties Based on the Average of One Ring of Plates . . . . . . . . . . . . . . . 1-4-39 Live Loads, Including Impact, for Various Heights of Cover for Cooper E 80 . . . . . . . . . . . . . 1-4-40 Longitudinal Seam Strengths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-85 1-4-86 1-4-88 SECTION 4.1 LOCATION AND TYPE 4.1.1 WATERWAY REQUIRED (1995) Determination of the proper size culvert opening requires knowledge of the drainage area, runoff, data on past performance, such as highwater marks above, at and below the opening, and pertinent formulas, with experience and good judgment in interpreting them. Consideration of the stream both above and below the opening is necessary. The ideal opening is one in which the velocity of the stream above the opening is maintained or somewhat increased through the opening and below to a point where the flow will have no effect on the railway. See Part 3, Natural Waterways. 4.1.2 SPAN REQUIRED (1995) a. The span of the culvert should be such that the property above will not be injuriously affected at time of maximum runoff, nor a head created which will induce destructive velocities. b. In shallow fills the span may have to be increased to provide the predetermined area. For pipe culverts, where practical, the cover should be a minimum of 22 feet below the bottom of tie. c. For practical reasons, a minimum size pipe culvert should be established, even though runoff computations may show that a size smaller than the minimum might be used. For main line track a minimum diameter of 24 inches is recommended, while for highway crossings and unimportant track, the minimum diameter may be reduced to 18 inches. Pipe structures smaller than these are difficult to clean out and may be of insufficient capacity if freezing occurs. 4.1.3 CHARACTER OF HYDRAULIC BEDLOAD (ABRASIVE, CORROSIVE, ETC.) (1995) a. Except in localities of such special service classifications as mineralized, organic, and salt water, which are relatively small in area as compared with the entire country, corrosion from soil and water is far less important in shortening the life of drainage structures than is the abrasive action of the hydraulic bedload. So far as soil corrosion on the outside of structures is concerned, extensive soil corrosion tests of the Bureau of Standards show conclusively that in only about 10% of the soils is corrosion from the outside severe: that in about another 10% the corrosion is mildly severe, and that in more than 80% the soil corrosion is negligible. b. Turning to internal corrosion, mine water, especially from coal mines, is particularly difficult to handle as it attacks all commonly used materials except possibly well burnt vitrified clay pipe. c. The alkali soils are of two kinds, black alkali and white alkali. White alkali usually contains quantities of sulfates, carbonates or chlorides, which on evaporation of moisture in the soil leaves a white crust on the surface. The black alkali, a sodium carbonate, does not leave the white crust. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-6 AREMA Manual for Railway Engineering Culverts d. The white alkalies, particularly the sulfates, are more severe on concrete than metal. The black alkalies and the chloride salt alkalies, on the other hand, are relatively more severe on metal than on concrete. e. Sea water is injurious to all types of drainage materials. The chlorides in the salt water shorten the life of metal structures, while the alternate wetting and drying, and the frost action in cold climates accelerate the deterioration of concrete. f. Wherever the service conditions are such as to indicate severe abrasive or corrosive action, the available drainage material that will be least affected should be used, resulting in a structure that will give the lowest cost per year of service. 4.1.4 TOPOGRAPHIC CONDITIONS DETERMINING ANGLE, GRADIENT, AND LENGTH OF STRUCTURE (1987) a. A culvert, being an enclosed channel substituted for an open waterway, is a fixed section of what is possibly an unstable stream that is changing its course, scouring deeper, or filling up. The alignment, gradient and length of the structure should therefore be determined so as to obtain the most economical safe installation. b. The best alignment is that which gives the water a straight entrance into the culvert and a direct exit. A stream that is very crooked, or one that is changing its course, may possibly be relocated to make it cross the roadbed at or near a right angle, but the best general principle is to make the alignment of the structure coincide as nearly as possible with that of the stream. c. A culvert should usually be given the same general gradient as the stream bed. One of the most common mistakes is to place the invert at the same elevation as the stream bed. The result is that sedimentation reduces the effective area of the opening. d. Under new fills where there is a possibility of subsidence of the natural ground thereunder, culverts should be laid or constructed with sufficient camber so that there will be no dips or depressions in the culvert when subsidence has stopped. e. The length of a culvert depends upon the shoulder-to-shoulder width of the roadbed, the height of fill, the slope of the embankment, the gradient of the culvert, the skew angle, and whether or not headwalls are to be built. The best method of determining the required length is by the use of a cross-sectional sketch of the embankment and a plan and profile of the water course. 4.1.5 FOUNDATION CONDITIONS (1987) Every structure should have the best foundation possible to obtain within the limits of the allowable cost for the structure. But it is not always possible to obtain a satisfactory foundation for some types of structures at a reasonable cost, and it is in these cases that cost comparisons may play an important part in the choice of the type of structure to be used. The heavier a structure is per foot of length, the greater the required bearing power of the soil underneath. In the case of rigid types of structures, cradling or even piling is sometimes necessary. In all cases backfill should be thoroughly tamped and compacted to a minimum 90% density as determined by ASTM D-698. 4.1.6 HEIGHT AND CHARACTER OF EMBANKMENT (1987) A factor that must be considered in the selection of structures is that of transverse forces in fills. These forces are manifested by the tendency of the fill material to move downward and outward, seeking its angle of repose and tending to separate the lengths of pipe culverts and open cracks in masonry. Transverse forces are present in every fill but are likely to be particularly severe on sidehill locations. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-7 1 3 4 Roadway and Ballast 4.1.7 LOADING, LIVE AND DEAD (1984) Extensive research work on the problem of culvert loading and design has been done. The results of this research are given in the following references: a. Iowa State Experiment Station, Ames, Iowa. Bulletin 79, “Experimental Determination of Static and Impact Loads Transmitted to Culverts.” Bulletin 96, “Theory of External Loads on Closed Conduits.” Bulletin 112, “The Supporting Strength of Rigid Pipe Culverts.” b. American Railway Engineering Association, Proceedings, Vol. 27, 1926, page 794, Proceedings, Vol. 29, 1928, page 527. Discussion and analysis of culvert loading and failures as developed by tests carried out under the sponsorship of this committee at various points, including the Farina test under high fills on the then new Edgewood cutoff of the Illinois Central Railroad. These tests involved both rigid and flexible type culverts. c. A culvert pipe placed under an embankment derives its ability to support the superimposed load from two sources: (1) The strength of the pipe ring or shell to resist external pressures; this may be termed inherent strength, and, (2) The lateral pressure of the embankment material upon the sides or vertical projection of the pipe, producing stresses in the pipe ring directly opposite to those produced by the vertical load and therefore assisting the pipe in supporting the vertical load. In a rigid pipe, such as concrete, cast iron, vitrified clay, etc., the inherent strength of the pipe is the predominant source of supporting ability. The only lateral pressure that can be safely depended upon to augment the load-carrying capacity of the pipe is the active lateral pressure of the embankment material since the rigid pipes deform but little, if any, under the vertical load and consequently the sides do not move outward enough to develop any appreciable passive resisting pressure in the surrounding embankment material. In a flexible pipe considerable strength is obtained through ring compression, but in bending (flexural) strength is low. Therefore, a large part of its ability to support the vertical load must be derived from the passive pressures induced or set up as the sides move outward against the surrounding material. The ability of a flexible pipe to deform readily without failure and thus utilize the passive pressures set up on the sides of the pipe is its principal distinguishing structural characteristics and accounts for the fact that such a relatively lightweight pipe of low inherent strength can support high embankments without showing evidence of structural distress. 4.1.8 ECONOMICS OF VARIOUS TYPES (1984) a. Requirement of any opening is a suitable continuing passageway for the water. Any economic study must include (1) interest on the investment, (2) maintenance costs, and (3) provision for an annual payment which will accumulate to a sufficient amount to replace the structure at the end of its useful life (or retire bonds sold to secure funds for the existing structure – the result being the same from an economic study standpoint). The sum of these three charges is the annual cost. The principle involved is long established and widely used. b. To arrive at the amount of interest on the investment, the initial cost installed must be determined. The items included in the cost are: Engineering; superintendence; labor; material, tools, equipment, supplies, and transportation and handling thereof, including stores expense; for supporting tracks – sheeting, shoring, pumping, excavation, including channel changes, building the structure, backfilling and restoring the tracks; all the costs from inception to completion. c. In preparing cost estimates, different methods of installation should be investigated. Under some conditions, when using pipe, a sizable saving can be made by such methods as tunneling, threading, and jacking. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-8 AREMA Manual for Railway Engineering Culverts d. Having arrived at the cost of the structure ready for service, the first item of annual cost is obtained by multiplying this initial cost by the average interest rate paid on railroad bonds over a period of years. e. The second item is that of maintenance, the estimate of which should be based upon actual records of costs of maintenance of similar structures. f. The third item, replacement annuity, is dependent upon the sum necessary to be accumulated, the rate of return on sinking funds, and the useful life of the structure. With this information and a table of annuities, the third item in the annual cost formula is easily obtained. g. The useful life for structures of various types should be estimated for each major service classification, from records of the company, or from an examination of structures in each service classification that have been in service for at least 5 to 10 years. Much can be learned from painstaking field inspection of existing structures if all factors affecting the performance of the structures are taken into consideration. h. Since cost comparisons are so easily made, and since it is one of the chief functions of a railroad engineer to operate the road, in so far as his sphere of influence extends, at the lowest true annual cost possible, economic comparisons should be made one of the guides toward the selection of drainage structures. SECTION 4.2 SPECIFICATIONS FOR PLACEMENT OF REINFORCED CONCRETE CULVERT PIPE 1 See Chapter 8, Concrete Structures and Foundations, Part 10, Reinforced Concrete Culvert Pipe. SECTION 4.3 SPECIFICATIONS FOR PREFABRICATED CORRUGATED STEEL PIPE AND PIPE-ARCHES FOR CULVERTS, STORM DRAINS, AND UNDERDRAINS 3 4.3.1 GENERAL (1989) 4.3.1.1 Scope 4 This specification covers coated, prefabricated corrugated steel pipe and pipe arches for use as culverts, storm sewers and underdrains. 4.3.1.2 Class Pipe and pipe arches shall be of the following classes with respect to corrugations (See Table 1-4-1): • Class I Annular corrugations. • Class II Helical corrugations. 4.3.1.3 Shape Pipe and pipe arches shall be of the following cross-sectional shapes: © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-9 Roadway and Ballast • Shape 1 Pipe, full circular cross section. • Shape 2 Pipe, factory elongated. • Shape 3 Pipe arch cross section. 4.3.2 MATERIAL (1989) 4.3.2.1 Steel Sheets Corrugated steel pipe and pipe arches shall be fabricated from either of the following materials: • Steel sheet, zinc coated in accordance with AASHTO M-2l8. • Steel sheet, aluminum coated in accordance with AASHTO M-274. 4.3.2.2 Rivets All rivets shall conform to the specifications of ASTM designation A31, Grade A, and shall be electroplated in accordance with the specifications of ASTM designation A 164, Type RS. 4.3.3 FABRICATION (1989) 4.3.3.1 Corrugations The corrugations shall form smooth, continuous curves and tangents. The crests and valleys of annularly corrugated pipe and pipe arches shall form circumferential rings about the longitudinal axis of the pipe. The crests and valleys of helically corrugated pipe and pipe arches shall form helices about the longitudinal axis of the pipe, and the direction of the corrugations shall be not less than 45 degrees from the longitudinal axis of the pipe. The dimensions of the corrugations shall be as specified in Table 1-4-1. Table 1-4-1. Corrugations Class I II Diameter Nominal Size Maximum Pitch Minimum (Note 1) Inside Radius 8–96 2-2/31/2 2-3/4 11/16 12–96 31 3-1/4 9/32 6–18 1-1/21/4 1-7/8 9/32 12–96 2-2/31/2 2-3/4 11/16 48–120 31 3-1/4 9/32 48–120 51 5-1/4 1-9/32 Note 1: Pitch is measured at right angles to the corrugation. Note 2: Depth shall not overrun by more than 5%. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-10 AREMA Manual for Railway Engineering Culverts 4.3.3.2 Perforations for Underdrains Perforations, unless otherwise specified, shall be arranged in two groups of longitudinal rows placed symmetrically on each side of an unperforated segment corresponding to the flow line of the pipe. The longitudinal rows within each group shall be spaced on approximately 1-1/2 inches centers in annularly corrugated pipe and on approximately 1 inch centers on helically corrugated pipe. The perforations shall have a diameter of approximately 3/8 inch and shall be located on the inside crests, or on the neutral axis, of all corrugations except that perforations are not required within 6 inches of each pipe or in the crests of corrugations where seams are located. The minimum number of longitudinal rows of perforations and the minimum width of the unperforated segment shall be as shown in Table 1-4-2. Table 1-4-2. Perforations Nominal Inside Diameter Inches Minimum Number or Rows of Perforations Minimum Width of Unperforated Segment Inches 6 4 4 8 4 7 10 4 9 12 6 9-1/2 15 6 13 18 6 16-1/2 21 6 20 24 8 22 1 3 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-11 Roadway and Ballast 4.3.3.3 Widths of Laps (Class I Annular Pipe) a. The lapped joints in longitudinal seams shall be as shown in Table 1-4-3. b. The average inside diameter of circular pipe and pipe to be reformed into pipe arches shall not vary more than 1/2 inch from the nominal diameter when measured on the inside crest of the corrugations for diameters through 48 inches and 1% for diameters greater than 48 inches. In no case shall the difference in diameter of the abutting pipe ends be more than 1/2 inch. Table 1-4-3. Pipe Requirements Nominal Inside Diameter Inches Corrugation Depth Nominal Inches Minimum Width or Lap Inches 8 1/2 1-1/2 10 1/2 1-1/2 12 1/2 1-1/2 15 1/2 1-1/2 18 1/2 1-1/2 21 1/2 1-1/2 24 1/2 2 30 1/2 2 36 1/2 2 36 1 3 42 1/2 or 1 3 48 1/2 or 1 3 54 1/2 or 1 3 60 1/2 or 1 3 66 1/2 or 1 3 72 1/2 or 1 3 78 1/2 or 1 3 84 1/2 or 1 3 90 1 3 96 1 3 102 1 3 108 1 3 114 1 3 120 1 3 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-12 AREMA Manual for Railway Engineering Culverts 4.3.3.4 Riveted Seams a. Rivets shall be of the diameter shown in Table 1-4-4. Table 1-4-4. Riveted Seams Gage b. Sheet Thickness Inches Rivet Diameter Inches 2-2/3 x 1/2 31 16 0.064 5/16 3/8 14 0.079 9/32 3/8 12 0.109 3/8 7/16 10 0.138 3/8 7/16 8 0.168 3/8 7/16 All rivets shall be cold driven in such a manner that the metal shall be drawn tightly together throughout the entire lap. The center of each rivet shall be not closer than 2 rivet diameters from the edge of the sheets. All rivets shall have full hemispherical heads or heads of a form acceptable to the engineer. They shall be driven in a neat, workmanlike manner to completely fill the hole without bending. Longitudinal seams shall be riveted with one rivet in each corrugation for pipes less than 42 inches in diameter and two rivets in each corrugation for pipes 42 inches in diameter and larger. Circumferential seams shall be riveted with a rivet spacing of 6 inches except that six rivets will be sufficient in 12 inches diameter pipe. The longitudinal seams of all 1 inch corrugated depth shall be two rivets in each corrugation. 1 4.3.3.5 Welded Seams (Class II Helical Pipe) Helically corrugated welded seam pipe shall have a continuous welded seam extending from end to end of each length of pipe section. The welded seam shall be of the high-frequency resistance butt welded type and shall be sufficiently strong to develop the full strength of the pipe. 4.3.3.6 Lock Seams (Class II Helical Pipe) Helically corrugated lock seam pipe shall have a continuous folded lock seam extending from end to end of each length of pipe section. Folded lock seams shall be formed with sufficient pressure to prevent any seam slippage that would seriously affect the load-carrying capacity of the pipe but without damaging the metal to such an extent that a plane of weakness is created. The metal used in fabricating lock seam shall be one that will permit cold forming without damage. 4.3.4 COUPLING BANDS (1989) a. Field joints for each class of corrugated steel pipe shall provide circumferential and longitudinal strength to preserve the pipe alignment, prevent separation of pipe and prevent infiltration of side fill material. The coupling bands shall be made of the same base metal as the pipe and shall be similarly coated. Coupling bands may be the next thickness lighter than that used for the pipe but not more than 0.109 inch (12 gage) nor less than 0.052 inch (18 gage). To facilitate field jointing, the ends of individual pipe section with helical corrugations may be rerolled to form circumferential corrugations extending at least two corrugations from the pipe end. All types of pipe ends, whether rerolled or not, shall be matched in a joint such that the maximum difference in the diameter of abutting pipe ends is 2 inch. b. Class I pipe furnished with circumferential corrugations, including rerolled end helical pipe, shall be field jointed with locking bands. The corrugated bands shall be not less than 7 inches wide for diameters through 36 inches, and 102 inches wide for all other pipe diameters. Wider bands should be considered where transverse forces are present, particularly on side hill slopes. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-13 3 4 Roadway and Ballast c. Class II pipe with helical corrugations shall be field jointed, preferably with bands with projections. The projections shall conform substantially to the shape and depth of the pipe corrugations and shall be in circumferential rows with one projection for each corrugation of helical pipe. Bands shall be so constructed as to lap on an equal portion of each of the culvert sections to be connected. The bands for pipe diameters of 12 inches to 54 inches incl., shall be at least 102 inches wide and shall have two circumferential rows of projections: and for pipe diameters 60 inches and greater shall be at least 163 inches wide and shall have four circumferential rows of projections. The band shall be connected in a manner approved by the chief engineer or his representative, with a suitable fastening device such as galvanized 2 inches by 2 inches by 3/16 inch angles, or integrally or separately formed and attached flanges bolted with 2 inch-in-diameter galvanized bolts, or a wedgelock constructed of the same gage as the band itself. The 102 inches band shall have two, and the 163 inches band shall have three 2 inch band shall have two, and the 163 inches band shall have three 2 inch diameter galvanized fastening bolts. d. Underdrain pipe may be field jointed with bands as described above or with a smooth sleeve-type coupler. The sleeve-type coupling may be either plastic or galvanized steel, suitable for holding the pipe firmly in alignment without the use of sealing compound or gaskets. Integral formed flanges fastened with 3/8 inch diameter galvanized bolts may be used in lieu of angles on two-piece corrugated bands. e. Other equally effective types of coupling bands and/or band-fastening devices may be used if approved by the chief engineer or his representative. 4.3.5 SHAPE (1989) a. Class I and Class II pipe shall be furnished, as specified, as Shape 1, Shape 2 or Shape 3. b. Shape 1 pipe shall be round pipe, available in diameters of 6 inches to 120 inches, incl. c. Shape 2 pipe shall be factory elongated to form an approximate ellipse with the vertical diameter approximately 5% greater than the nominal diameter of the corresponding round pipe. Shape 2 pipe shall be available in nominal diameters of 48 inches to 120 inches incl. d. Shape 3 pipe arch shall be fabricated by reforming a circular pipe to a multi-centered pipe having an archshaped top with a slightly convex integral bottom. The pipe-arch shall conform to the requirements of Table 1-4-5 and Table 1-4-6. The longitudinal seams of riveted pipe arches shall not be placed in the haunch area. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-14 AREMA Manual for Railway Engineering Culverts Table 1-4-5. Pipe Arch Specification Requirements Pipe Arches – 2-2/3 1/2 Corrugations (See Note 3) Pipe Arch Size Inches Equivalent Diameter Inches Span Inches (Note 1) Rise Inches (Note 1) Minimum Corner Radius Inches Maximum B Inches (Note 2) 17 13 21 15 15 17 13 3 5-1/4 18 21 15 3 6 24 18 21 24 18 3 7-1/4 28 20 35 24 24 28 20 3 8 30 35 24 3 9-1/2 42 29 49 33 36 42 29 3-1/2 10-1/2 42 49 33 4 11-1/2 57 38 64 43 48 57 38 5 13-1/2 54 64 43 6 15 71 47 77 52 60 71 47 7 16-1/2 66 77 52 8 18 1 83 57 72 83 57 9 20 Note 1: A tolerance of ±1 or 2% of equivalent circular diameter, whichever is greater, will be permissible in span and rise. Note 2: B is defined as the vertical dimension from a horizontal line across the widest portion of the arch to the lowest portion of the base. Note 3: All dimensions are measured from the inside crests of the corrugations. 3 Table 1-4-6. Pipe Arch Specification Requirements Pipe Arches – 3 1 and 5 1Corrugations (See Note 2) Pipe Arch Size Inches Equivalent Diameter Inches Span Inches (Note 1) Rise Inches (Note 1) Minimum Corner Radius Inches 40 31 46 36 36 40–1.8 31+1.8 5 42 46–2.1 36+2.1 6 53 41 60 46 48 53–2.4 41+2.4 7 54 60–2.7 46+2.7 8 66 51 73 55 60 66–3.0 51+3.0 9 66 73–3.3 55+3.3 12 81 59 87 63 72 81–3.6 59+3.6 14 78 87–4.4 63+4.4 14 95 67 84 95–4.8 67+4.8 16 103 71 112 75 90 103–5.2 71+5.2 16 96 112–5.6 75+5.6 18 117 79 102 117–5.9 79+5.9 18 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-15 Roadway and Ballast Table 1-4-6. Pipe Arch Specification Requirements Pipe Arches – 3 1 and 5 1Corrugations (See Note 2) (Continued) Pipe Arch Size Inches Equivalent Diameter Inches Span Inches (Note 1) Rise Inches (Note 1) Minimum Corner Radius Inches 128 83 137 87 108 128–6.4 83+6.4 18 114 137–6.9 87+6.9 18 120 142–7.1 91+7.1 18 142 91 Note 1: Negative and positive numbers listed with span and rise dimensions are negative and positive tolerances. Note 2: All dimensions are measured from the inside crests of the corrugation. 4.3.6 WORKMANSHIP (1989) Pipe shall show careful, finished workmanship in all particulars and shall be free from the following defects: a. Undue deviation from true shape. b. Uneven laps. c. Variations from a reasonably straight center line. d. Ragged or diagonally sheared edges. e. Loose, unevenly lined or spaced rivets, or welds. f. Poorly formed rivet heads. g. Illegible brand. h. Dents or bends, other than corrugations. i. Poor welds. j. Poorly formed lock seams and/or damaged lock seam metal. k. Bruised, scaled or broken coating. 4.3.7 MILL OR SHOP INSPECTION (1989) If the purchaser so elects, he may have the material inspected in the shop where it is fabricated. He may require from the mill that a chemical analysis be made of any heat. The purchaser, or his representative, shall have free access to the mill or shop for inspection purposes, and every facility shall be extended to him for this purpose. Any material included in any shipment which has been rejected at the mill or shop will be considered sufficient cause for the rejection of the entire shipment. 4.3.8 FIELD INSPECTION AND ACCEPTANCE (1989) The field inspection shall be made by the purchaser, who shall be furnished by the seller with an itemized statement of the sizes and lengths of pipe for deficiencies in length of sheets used, nominal specified diameter, net © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-16 AREMA Manual for Railway Engineering Culverts length of finished pipe and any evidences of poor workmanship as outlined above. The inspection may include the taking of samples for chemical analysis and determination of weight of zinc coating. If 25% of the pipe in any shipment fails to meet all the requirements of this specifications, the entire shipment may be rejected. SECTION 4.4 SPECIFICATIONS FOR COATED CORRUGATED STEEL PIPE AND ARCHES 4.4.1 SPECIFICATION FOR BITUMINOUS COATED GALVANIZED STEEL PIPE AND PIPE ARCHES (1989) Corrugated steel galvanized pipe or pipe arches shall be bituminous coated or coated and paved in accordance with current AASHTO Specification M-190. 4.4.2 SPECIFICATION FOR POLYMERIC COATED CORRUGATED GALVANIZED STEEL PIPE OR PIPE ARCHES (1989) Corrugated steel galvanized pipe or pipe arches shall be polymeric coated in accordance with current AASHTO Specification M-246. 1 SECTION 4.5 STANDARD SPECIFICATION FOR CORRUGATED ALUMINUM ALLOY PIPE 4.5.1 GENERAL (1989) 3 4.5.1.1 Scope This specification covers corrugated aluminum pipe for use as culverts, storm drains, and underdrains. 4.5.1.2 Class 4 Pipe and pipe arches shall be of the following classes with respect to corrugations (See Table 1-4-10): • Class I – Annular corrugation. • Class II – Helical corrugation. 4.5.1.3 Shapes Pipe and pipe arches shall be of the following cross-sectional shapes: • Shape 1 – Pipe, full circular cross-section. • Shape 2 – Pipe, factory elongated. • Shape 3 – Pipe arch cross section. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-17 Roadway and Ballast 4.5.2 MATERIAL (1989) 4.5.2.1 Sheet or Coil Corrugated aluminum pipe and pipe arches shall be fabricated from clad 3004 H34 aluminum sheets or in coil cutto-length conforming to the current ASTM specification designation B-209 and latest AASHTO specification Ml97. The corrugations shall conform to the requirements set in Table 1-4-10. 4.5.2.2 Accepted Brands of Aluminum Alloy No aluminum alloy will be accepted under the specification and no bids will be considered for the materials above described until after the sheet manufacturer’s certified analysis and manufacturer’s guarantee has been passed upon by the engineer and accepted. Misbranding or other misrepresentation and non-uniformity of product will each be considered a sufficient reason to discontinue the acceptance of any brand under this specification and notice sent to the sheet manufacturer of the discontinuance of acceptance of any brand will be considered to be notice to all culvert companies which handle that particular brand. 4.5.2.3 Sheet Manufacturer’s Certified Analysis The manufacturer of each brand shall file with the engineer a certificate setting forth the name or brand of aluminum alloy to be furnished and a statement that the material conforms to the specified chemical composition limits. The certificates shall be sworn to for the manufacturer by a person having legal authority to bind company. 4.5.2.4 Sheet Manufacturer’s Guarantee The manufacturer of the sheets shall submit with the certified analysis a guarantee providing that all aluminum alloy furnished shall conform to the specification requirements, shall bear a suitable identification brand or mark, and shall be replaced without cost to the purchaser when not in conformity with the specified analysis, sheet thickness or cladding thickness, and the guarantee shall be so worded as to remain in effect as long as the manufacturer continues to furnish material. 4.5.2.5 Thickness All the thickness of both flat sheet or formed coil shall have the gage or decimal thickness found in Table 1-4-7. Table 1-4-7. Gage or Decimal Thickness Gage Specified Inches Minimum Inches 16 0.060 0.057 14 0.075 0.072 12 0.105 0.101 10 0.135 0.130 8 0.164 0.158 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-18 AREMA Manual for Railway Engineering Culverts 4.5.2.6 Chemical Composition The core metal and cladding shall conform to the chemical requirements of Table 1-4-8. Table 1-4-8. Chemical Composition Culvert Sheet Core % (Note 1) Type Culvert Sheet Cladding % (Note 1) Silicon 0.3 (Si + Fe) = 0.7 Iron 0.7 Copper 0.25 0.10 Manganese 1.0 – 1.5 0.10 Magnesium 0.8 – 1.3 0.10 Zinc 0.25 0.8 – 1.3 Other, each 0.05 0.05 Total 0.15 0.15 Note 1: Composition in percent maximum unless shown as range. 1 4.5.2.7 Mechanical Requirements The material shall conform to the mechanical properties of Table 1-4-9. Table 1-4-9. Mechanical Requirements Tensile Strength psi Minimum Maximum Yield Strength, psi (0.2% offset) Minimum 0.048 to 0.113 31,000 37,000 24,000 4 0.114 to 0.249 31,000 37,000 24,000 5 Thickness inches Elongation in 2% Minimum 3 4 4.5.2.8 Cladding Thickness The clad in each side shall be 5% of the total thickness. 4.5.2.9 Tests by Sheet Manufacturer Sampling and testing by the purchaser shall conform to the latest requirements as outlined in AASHTO M-197. 4.5.2.10 Dimensions and Tolerances The latest AASHTO M-197 specs shall be followed. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-19 Roadway and Ballast 4.5.2.11 Marking Each corrugated sheet or coil used in corrugated pipe shall be identified by the manufacturer and producer showing the following: a. Name of sheet manufacturer. b. Alloy and temper. c. Manufacturer’s standard thickness. d. Manufacturer’s date of corrugating by a six digit number indicating in order of the year, month, and day of the month. e. Identification of the pipe fabricator if different than the sheet manufacturer. 4.5.2.12 Rivets Rivets shall conform to the chemical composition shown in ASTM B-316 for alloy 6053 T4 and shall have the following mechanical properties: Tensile strength . . . . . . . . . . . . . 25,000 psi Yield strength . . . . . . . . . . . . . . . 14,000 psi Shear . . . . . . . . . . . . . . . . . . . . . . 15,000 psi Elongation . . . . . . . . . . . . . . . . . . 16% 4.5.3 FABRICATION (1989) Pipe under this section shall be fabricated with circumferential corrugation and riveted, lap joint construction or with helical corrugations and a continuous lock or welded seam extending from end to end each length of pipe. 4.5.3.1 Corrugations The corrugations shall form smooth, continuous curves and tangents. The radii of curvature of the corrugations shall be at least one-half the depth of the corrugations. The crests and valleys of annularly corrugated pipe and pipe arches shall form circumferential rings about the longitudinal axis of the pipe. The crests and valleys of helically corrugated pipe and pipe arches shall form helices about the longitudinal axis of the pipe, and the direction of the corrugations shall be not less than 45 degrees from the longitudinal axis of the pipe. The dimensions of the corrugations shall be as specified in Table 1-4-10. 4.5.3.2 Class I – Annular Corrugation Pipe under this class shall be of riveted fabrication. The corrugation shall be 2 inch from 12 inches to 84 inches or 1 inch from 36 inches to 90 inches diameter. 4.5.3.3 Width of Laps The lapped joints in circumferential seams shall be 1-1/2 inches. The lapped joints in longitudinal seams shall be 11/2 inches, for pipe diameters of 8 to 21 inches: 2 inches for pipe diameters of 24 inches, 30 inches, and 36 inches; and 3 inches for pipe diameters of 42 to 90 inches. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-20 AREMA Manual for Railway Engineering Culverts Table 1-4-10. Dimensions of Corrugations Corrugations Class (Note 3) I (Annular) II (Helical) Depth Inches (Note 2) Pitch Inches Diameter Inches Minimum (Note 1) Maximum (Note 1) 12 – 84 2-1/4 2-3/4 1/2 1 36 – 120 2-3/4 3-1/4 36 – 120 5-3/4 6-1/4 1 6, 8, 10 1-3/8 1-7/8 1/4 12 – 21 2-1/4 2-3/4 7/16 12 – 84 2-1/4 2-3/4 1/2 30 – 90 2-3/4 3-1/4 1 Note 1: The pitch shall be measured at right angles to the corrugations. Note 2: The depth shall not underrun by more than 5%. Note 3: Underdrains – Pipe is available with or without perforations. 1 4.5.3.4 Riveted Seams a. Rivets shall be of the diameter for either the sheet thickness or pipe diameter or both as shown in Table 1-411. All rivets shall be cold driven in such a manner that the metal shall be drawn tightly together throughout the entire lap. The center of each rivet shall be not closer than 2-rivet diameter from the edge of the sheets. All rivets shall have full hemispherical heads or heads of a form acceptable to the engineer. They shall be driven in a neat, workmanlike manner to completely fill the hole without bending. Table 1-4-11. Minimum Rivet Diameter (See Note 3) 3 Corrugation Thickness Inches 2-2/3 x 1/2 (Note 1) 3x1 (Note 2) 0.060 5/16 0.075 5/16 3/8 3/8 0.105 3/8 3/8 3/8 0.135 0.164 4 1/2 1/2 1/2 Note 1: One rivet each valley for pipes 36 inches and smaller. Two rivets each valley for pipes 42 inches and larger. Note 2: Two rivets each valley for all diameters. Note 3: Rivet sizes shown are minimum. Larger rivets or additional rivets are permissible if necessary to increase seam strength. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-21 Roadway and Ballast b. Longitudinal seams for 7/16 inch and 2 inch, shall be riveted with one rivet each corrugation for pipes less than 42 inches in diameter, and two rivets in each corrugation for pipes 42 inches in diameter and larger. The longitudinal seams of 1 inch corrugation depth shall be riveted with two lines of rivets spaced longitudinally on 3 inches center. The distance between center lines of two rivet rows shall not be less than 12 inches. For 1 inch depth corrugations, in lieu of shop riveting, pipe may be field assembled using 2 inch diameter aluminized or galvanized steel bolts. Spacing and location of field bolts will be the same as spacing and location of shop rivets. 4.5.3.5 Class II – Helical Corrugation Pipe under this class shall be helically corrugated pipe with continuous lock seam extending from end to end of each pipe. The corrugation requirements are as outlined in Article 4.5.3.1. The corrugation for helical pipe is shown in Table 1-4-10. a. Pipes fabricated with a continuous helical lock seam parallel to the corrugation may be used for full circle and equivalent pipe arch sizes. b. The lock seam shall be formed in the tangent element of the corrugation profile with its center near the neutral axis of the corrugation profile. The edges of the sheets within the cross section of the lock seam shall lap at least 5/32 inch for the pipes 10 inches or less in diameter and at least 5/16 inch for pipe greater than 10 inches in diameter with an occasional tolerance of minus 10% of lap with allowable. c. The lapped surfaces shall be in tight contact. The profile of sheet on at least one side of the lock seam and adjacent to the 180 degrees fold shall have a minimum retaining offset of 2 sheet thickness. There shall be no excessive angularity on the interior of the 180 degrees fold of metal at the lock seam which will cause visual cracks in the sheet. Roller indention shall not cause cracks in the sheet or a loss of metal contact within the seam. d. The lock seam shall be mechanically staked at periodic intervals or otherwise specially constructed to prevent slippage. Tensile specimens cut from production pipe normal to and across the lock seam develop the strength as tabulated in Table 1-4-12. Table 1-4-12. Pipe Sheet Thickness to Lock Seam Strength Pipe Sheet Thickness Minimum Lock Seam Strength Inches Pounds/Inch 0.060 170 0.075 245 0.105 425 4.5.4 COUPLING BANDS – CLASS I AND CLASS II (1989) a. Field joints for pipe sections shall be made with coupling bands which will provide the circumferential and longitudinal strength required to preserve the pipe alignment and to prevent separation of pipe sections, thereby minimizing infiltration of fill material. Coupling bands shall be made of the same alloy material as the pipe, shall have corrugations that mesh with the corrugations of the pipe sections to be connected, and shall be formed to fit the shape specified for those sections. The bands shall be not more than one standard use thickness lighter than that used for the pipe sections to be connected, but never less than 0.048 inch material. The bands shall be fabricated to lap on an equal portion of each of the sections connected. b. Bands with corrugations shall be not less than 7 inches wide for pipe 12 inches to 30 inches in diameter, not less than 12 inches for pipe diameters 36 inches to 60 inches, inclusive, and not less than 24 inches for pipe diameters 66 inches and larger. The 1 inch depth corrugation shall always have 2 feet wide bands. Wider © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-22 AREMA Manual for Railway Engineering Culverts bands should be considered where transverse forces are present, particularly on sidehill slopes. The bands shall have 2 inches by 2 inches by 3/16 inch aluminum alloy connection angles conforming to ASTM B22 1, alloy 6063-T6, welded or riveted securely to the band ends. Aluminum alloy lugs or integrally formed flanges are acceptable in lieu of angles. c. The bands shall be installed as specified and tightened in place by not less than 2 inch galvanized steel bolts or aluminized steel bolts through the vertical legs of connection angles. Bands 7 inches wide shall have 2 bolts; 12 inches bands, 3 bolts; and 24 inches bands, 4 bolts. d. Perforated pipe may be joined with bands as described above. For pipe diameters 12 inches to 36 inches, inclusive, one-piece coupling bands utilizing a slip seam may be specified. This device provides for coupling band expansion by mechanically slipping the lock seam so that the coupler may be slipped over the ends of the pipe sections to be connected. The coupler is drawn snug over the pipe by reversing the method of slipping the seam and is then tightened to prevent further slippage. Mechanical slipping of seams is effected by means of a 2 inch bolt with double reverse threads used in conjunction with extruded aluminum lugs tapped to receive the 2 inch threaded bolt and welded to the band, one on each side of the helical seam. e. Other equally effective coupling bands or methods for connecting the pipe sections may be used when specified or if approved by the Chief Engineer. 4.5.5 SHAPE – CLASS I AND CLASS II (1989) 1 Class I and Class II pipe shall be furnished as specified as Shape 1, Shape 2 or Shape 3. 4.5.5.1 Shape 1 Shape 1 pipe shall be round pipe, available in diameter of 6 inches to 90 inches inclusive. 4.5.5.2 Shape 2 3 Shape 2 pipe shall be factory elongated to form an approximate ellipse with the vertical diameter approximately 5% greater than the nominal diameter of the corresponding round pipe. Shape 2 pipe available in normal diameter of 48 inches to 90 inches inclusive. 4.5.5.3 Shape 3 Shape 3 pipe arch shall be fabricated by reforming a circular pipe to a multi-centered pipe having an arch-shaped top with a slightly convex integral bottom. Class I pipe to be reformed into pipe arch shall have the longitudinal lapped seams staggered so as to alternate on each side of the top center line by approximately 10% of the periphery. The pipe arch shall conform to the equivalents of Table 1-4-5 and Table 1-4-6 under specifications for corrugated steel pipe. SECTION 4.6 SPECIFICATIONS FOR CORRUGATED STRUCTURAL STEEL PLATE PIPE, PIPE-ARCHES, AND ARCHES NOTE: Design of structural steel plate pipes, pipe arches and arches are based on empirical rules. 4.6.1 GENERAL (1989) These specifications cover corrugated structural steel plate pipe, pipe arch, and arch culverts 60 inches or more in diameter or in span. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-23 4 Roadway and Ballast 4.6.2 MATERIAL (1989) 4.6.2.1 Description of Plates a. Plates shall consist of structural units of galvanized corrugated steel. The corrugations shall run at right angles to the longitudinal axis of the structure and shall have a pitch of 6 inches, with a tolerance of 3 inch and a depth of 2 inches, with a tolerance of 1/8 inch. The radius of the inside of the corrugation shall be at least 1-1/16 inches. Plates shall be furnished in standard sizes to permit structure length increments of 2 feet. Plates shall have approximately a 2 inches lip beyond each end crest. b. The gage of plates and radii of curvature shall be as specified. The plates at longitudinal and circumferential seams shall be connected by bolts. Joints shall be staggered so that not more than three plates come together at any one point. Each plate shall be curved to a circular arc. c. Plates for a pipe arch, when assembled, shall form a cross section made up of four circular arcs tangent to each other at their junctions and symmetrical about the vertical axis. Pipe arches shall be installed with the flat side down. 4.6.2.2 Base Metal The base metal of the corrugated steel plates shall conform to the requirements of current ASTM Specification, Designation A-761. 4.6.2.3 Spelter Coating a. A coating of prime western spelter, or equal, of not less than 12 oz. per square foot on each surface for 0.188 inch or thicker and 1 oz. per square foot on each surface less than 0.188 inch in thickness shall be applied by the hot-dip process. If the average spelter coating as determined from the required samples is less than the amount specified above, or if any one specimen shows a deficiency of 10%, the lot sampled shall be rejected. Spelter coating shall be of first-class commercial quality, free from injurious defects, such as blisters, flux and uncoated spots. b. The sheets are to be galvanized after fabrication. 4.6.2.4 Physical Properties a. b. The minimum physical properties of the flat sheet or plate before corrugation shall be as follows: Tensile strength, psi. . . . . . . . . . 42,000 Yield point, psi . . . . . . . . . . . . . . 28,000 Elongation in 2, %. . . . . . . . . . . 30 The supplier shall certify that the tests performed on each heat of the material furnished meet the above requirements. 4.6.2.5 Sampling For testing the weight of the spelter coating and for chemical analysis of the base metal, when required, a sample approximately 3 inch square, or a sample of equivalent area, shall be cut from the corner of one plate in each 100 plates of a shipment or fraction thereof, or coupons approximately 6 inch square of the same gage and base metal as the material sampled shall be attached to the center of one edge of the plates before galvanizing. If the result of a weight of coating test for any coupon does not conform to the requirements specified, retests of two additional samples cut from the product plates for the order shall be made, each of which shall conform to the requirements specified. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-24 AREMA Manual for Railway Engineering Culverts 4.6.2.6 Test for Spelter Coating The test for weight of spelter coating shall be made in accordance with the hydrocholoric acid-antimony chloride method, as described in current ASTM Specification, Designation A 90. 4.6.2.7 Identification a. No plates shall be accepted unless the metal is identified by a stamp on each plate showing: (1) Name of base metal manufacturer. (2) Name of brand and kind of base metal. (3) Gage number. (4) Weight of spelter coating. (5) Identification symbols showing heat number. b. The identification brands shall be so placed that when the pipe or arch is erected the identification will appear on the inside of the structure. 4.6.2.8 Bolts a. Bolts for connecting plates shall be not less than 3/4 inch in diameter, of proper length to accommodate the number of plate laps, and the bolts and nuts shall be hot-dip galvanized to conform with the requirements of the current ASTM Specification, Designation A. 153. The threads shall be American Standard Coarse Thread Series, Class 2, free fit. Bolt and nut materials shall conform to the requirements of the current ASTM Specification, Designation A 449 and A 563 Grade C respectively. b. The bolts may be sampled and tested before erection is commenced or the bolts may be accepted on the manufacturer’s certification. c. Bolt heads and nuts, shaped to provide adequate bearing, shall be used. 1 3 4.6.2.9 Gage Determination and Tolerance The gage shall be determined by the weight of fabricated galvanized plates. The average weight of any one lot of plates shall not underrun the theoretical weight by more than 5%, and no individual plate weighed shall underrun the theoretical weight by more than 10%. 4.6.2.10 Field Inspection and Acceptance of Plates a. The field inspection shall be made by the engineer. The manufacturer shall furnish an itemized statement of the number and length of the plates in each shipment. b. Each plate included in a shipment failing to meet the requirements of these specifications shall be rejected, and if 25% of the plates fail to meet the requirements the entire shipment may be rejected. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-25 4 Roadway and Ballast 4.6.3 FABRICATION (1989) 4.6.3.1 Forming and Punching Plates a. Plates shall be formed to provide lap joints. The bolt holes shall be so punched that all plates having like dimensions, curvature, and the same number of bolts per foot of seam, shall be interchangeable. Each plate shall be curved to the proper radius so that the dimensions of the finished structure will be as specified. b. Unless otherwise specified, bolt holes along those edges of the plates that will form longitudinal seams in the finished structure shall be staggered in rows 2 inches apart, with one row in the valley and one in the crest of the corrugations. Bolt holes along those edges of the plates that will form circumferential seams in the finished structure shall provide for a bolt spacing of not more than 12 inches. The minimum distance from center of holes to the edge of the plate shall be 1-3/4 times the diameter of the bolt. The diameter of the bolt hole in the longitudinal seams shall not exceed the diameter of the bolt by more than 1/8 inch. c. Plates for forming skewed or sloped ends shall be cut so as to give the angle of skew or slope specified. Flame cut edges shall be free from oxide or burrs and shall present a workmanlike finish. Legible identification numerals shall be placed on each part plate to designate its proper position in the finished structure. d. When specified, the structural plate for round pipe shall be formed so as to provide, when assembled, an elliptical cross section having a vertical elongation of approximately 5%. SECTION 4.7 SPECIFICATIONS FOR CORRUGATED STRUCTURAL ALUMINUM ALLOY PLATE PIPE, PIPE-ARCHES, AND ARCHES NOTE: Design of structural aluminum alloy pipes, pipe arches and arches are based on empirical rules. 4.7.1 GENERAL (1989) These specifications cover aluminum alloy corrugated structural plate pipe, pipe arches and arch culverts 60 inches or more in diameter or in span. 4.7.2 MATERIAL (1989) 4.7.2.1 Description of Plates a. Plates shall consist of structural units of uncoated aluminum alloy. The corrugations shall run at tight angles to the longitudinal axis of the structure and shall have a pitch of 9 inches with a tolerance of 3/8 inch and a depth of 2-1/2 inches with a tolerance of 1/8 inch. The radius of the inside of the corrugation shall be not less than 2 inches. Plates shall have approximately a 2 inches lip beyond each end crest. b. The gage plates and radii of curvature shall be as specified. The plates at longitudinal and circumferential seams shall be connected by bolts. Joints shall be staggered so that not more than three plates come together at any one point. Each plate shall be curved to a circular arc. c. Plates for a pipe arch, when assembled, shall form a cross section made up of four circular arcs tangent to each other at their junctions and symmetrical about the vertical axis. Pipe arches shall be installed with the flat side down. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-26 AREMA Manual for Railway Engineering Culverts 4.7.2.2 Base Metal The plates shall be fabricated from aluminum alloy 5052-H141. The chemical composition of the plates shall conform to ASTM Designation B209 alloy 5052. Aluminum bolt and nut material shall conform to the Chemical requirements of ASTM Designation B-211 alloy 6061-T6. Bolts and nuts may be aluminum, aluminized steel, or galvanized steel. Extrusion material shall conform to the Chemical requirements of ASTM B22l alloy 6063-T6. 4.7.2.3 Physical Properties a. The minimum physical properties of the flat sheet or plate, bolts, nuts and extrusion are found in Table 1-413. b. The supplier shall certify that the tests performed on each heat of the material furnished meet the above requirements. Table 1-4-13. Flat Sheet or Plate, Bolts, Nuts, and Extrusion Physical Properties Thickness Inches Tensile Strength (psi) Yield Point (psi) Plate 0.100-0.174 35,500 24,000 6 Plate 0.175-0.300 34,000 24,000 8 Bolts 0.125-8.000 42,000 35,000 10 Extrusions 0.125-1.000 31,000 24,000 10 Item Elongation in 2 inches, % 1 4.7.2.4 Identification a. No plates shall be accepted unless the metal is identified by a stamp on each plate showing: 3 (1) Name of base metal manufacturer. (2) Name of brand and kind of base metal or alloy designation. (3) Manufacturer’s standard thickness. (4) Manufacturer’s date of processing by a six (6) digit number indicating in order the year, month, and day of month. b. The identification brands shall be so placed that when the pipe or arch is erected the identification will appear on the inside of the structure. 4.7.2.5 Bolts a. Bolts for connecting plates shall be not less than : inch in diameter, of proper length to accommodate the number of plate laps, and the bolts and nuts shall be hot-dip galvanized to conform with the requirements of the current ASTM Designations A 307 or A 325 or aluminum conforming with ASTM Designation B-211 alloy 6061. Aluminum nuts shall be prelubricated with a suitable wax compound. The threads shall be American Standard Coarse Thread Series, Class 2, free fit. b. The bolts may be sampled and tested before erection is commenced or the bolts may be accepted on the manufacturer’s certification. c. Bolt heads and nuts, shaped to provide adequate bearing, shall be used. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-27 4 Roadway and Ballast 4.7.2.6 Gage Determination and Tolerance The gage shall be determined by the weight of fabricated plates. The average weight of any one lot of plates shall not underrun the theoretical weight by more than 5%, and no individual plate weighed shall underrun the theoretical weight by more than 10%. 4.7.2.7 Field Inspection and Acceptance of Plates a. The field inspection shall be made by the engineer. The manufacturer shall furnish an itemized statement of the number and length of the plates in each shipment. b. Each plate included in a shipment failing to meet the requirements of these specifications shall be rejected, and if 25% of the plates fail to meet the requirements, the entire shipment may be rejected. 4.7.3 FABRICATION (1989) 4.7.3.1 Forming and Punching Plates a. Plates shall be formed to provide lap joints. The bolt holes shall be so punched that all plates having like dimensions, curvature, and the same number of bolts per foot of seam, shall be interchangeable. Each plate shall be curved to the proper radius so that the dimensions of the finished structure will be as specified. b. Unless otherwise specified, bolt holes along those edges of plates that will form longitudinal seams in the finished structure shall be in rows 1-3/4 inches apart, with a pair in the valley and crest of the corrugations. Bolt holes along those edges of the plates that will form circumferential seams in the finished structure shall provide for a bolt spacing of not more than 9-5/8 inches. The minimum distance from center of holes to the edge of the plate shall be 1-3/4 times the diameter of the bolt. The diameter of the bolt hole in the longitudinal seams shall not exceed the diameter of the bolt by more than 1/8 inch. c. When specified, the structural plate for round pipe shall be formed so as to provide, when assembled, an elliptical cross section having a vertical elongation of approximately 5%. SECTION 4.8 HYDRAULICS OF CULVERTS 4.8.1 INTRODUCTION (1989) a. Designing a culvert has not yet reached the stage where two or more individuals will always arrive at the same answer, or where actual service performance matches the designer’s anticipation. The reason is that the engineer’s interpretation of field data and hydrology is often influenced by personal judgment, based on his own experience in a given locality. However, field data, hydrology and hydraulic research are closing the gap to move the art of designing a culvert a little closer to becoming a science. b. Up to this point, the design procedure has consisted of collecting field data, compiling facts about the roadway, and making a reasonable estimate of flood flow for a chosen frequency. The fourth step is to design an economical culvert to handle the flow (including debris) with minimum damage to the right of way or adjacent property. c. Factors to consider include: type of structure; area and shape of waterway opening; approximate length and slope of culvert barrel; and treatment of inlet and outlet ends. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-28 AREMA Manual for Railway Engineering Culverts 4.8.2 DESIGN METHOD (1989) a. The culvert design process shall strive for a balanced result. Pure fluid mechanics should be combined with practical considerations to help assure satisfactory performance under actual field conditions. This includes prospective maintenance and the handling of debris. b. As a minimum, it is recommended that the culvert shall be designed to discharge: (1) a 25-year flood without static head at entrance, and (2) a 100-year flood using the available head at entrance, the head to 2 feet below base of rail, or the head to a depth of 1.5 times the culvert diameter/rise, whichever is less. c. This approach lends itself well to most modern design processes and computer programs such as those published by the Federal Highway Administration (Reference 21). It applies a usable rational control to the elusive matter of minimum waterway area which constitutes good practice. This design method is highly recommended and is followed here in conjunction with the Federal Highway Administration charts (Reference 22). However, the final decision regarding the appropriate method for sizing culverts is the responsibility of the design engineer. Other methods may be more appropriate for a given individual situation. d. The permissible height of water at the inlet controls hydraulic design, not vice versa. This should be stipulated for each site in which ponding is allowed, based on the following risk conditions: (1) Risk of overtopping the embankment, and attendant risk to human life. 1 (2) Potential damage to the roadway, due to saturation of the embankment. (3) Traffic interruptions. (4) Damage to adjacent, upstream and/or downstream property, or to the channel or flood plain environment. 3 (5) Intolerable outlet velocities, and scour and erosion. (6) Injurious deposition of bed load, and/or clogging by debris on recession of flow. (7) Operational requirements of the railroad. (8) Future repairs to the culvert. 4 4.8.3 FLOW CONDITIONS (1989) a. Conventional Culverts considered here are circular and oval pipes and pipe arches, with uniform barrel cross-section throughout. There are two major types of culvert flow – with inlet control or outlet control. b. Inlet Control. Under inlet control, the cross-sectional area of the barrel, the inlet configuration or geometry and the amount of headwater or ponding are primary importance (Figure 1-4-1). c. Outlet Control involves the additional considerations of the tailwater in the outlet channel, and the slope, roughness and length of barrel (Figure 1-4-2). 4.8.3.1 Hydraulics of Culverts in Inlet Control a. Inlet control means that the discharge capacity is controlled at the entrance by the headwater depth, crosssectional area and type of inlet edge. The roughness, length and outlet conditions are not factors in determining capacity. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-29 Roadway and Ballast b. Figure 1-4-1 shows both unsubmerged and submerged projecting entrances. c. Headwater depth, HW, shown in Figure 1-4-1 is the vertical distance from the culvert inlet at the entrance to the energy line of the headwater pool. d. Entrance loss, depends upon the geometry of the inlet edge and is expressed as a function of the velocity head. e. Research with models and some prototype testing have resulted in the use of the coefficients listed in Table 1-4-14 for various types of edge treatment. NOTE: Inlet control is one of the two major types of culvert flow. Condition A with unsubmerged culvert inlet is preferred to the submerged end. Slope, roughness and length of culvert barrel are of no consideration in inlet control. Figure 1-4-1. Inlet Control Table 1-4-14. Entrance Loss Coefficients for Corrugated Metal Pipe or Pipe Arch (Reference 22) Inlet End of Culvert Coefficient ke Projecting from fill (no headwall) 0.9 Headwall or headwall and wingwalls square-edge 0.5 Mitered (beveled) to conform to fill slope 0.7 End-Section conforming to fill slope (Note 1) 0.5 Headwall, rounded edge 0.2 Beveled Ring 0.25 Note 1: End Sections available from manufacturers. 4.8.3.2 Hydraulics of Culverts in Outlet Control HW = H + ho –LSo – Vl2/2g EQ 4-1 where: H = head, ft © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-30 AREMA Manual for Railway Engineering Culverts 1 NOTE: Outlet control involves these factors: cross-sectional area of barrel; inlet geometry; ponding; tailwater; and slope, roughness and length of culvert barrel. 3 Figure 1-4-2. Outlet Control ho = TW (under conditions shown in Figure 1-4-3 and Figure 1-4-4) L = Length of culvert, ft 4 So = slope of barrel, ft/ft Vl = approach velocity, ft/sec 4.8.3.3 Headwater Depth (HW) The head water depth is the vertical distance from the culvert invert at the entrance (full cross-section) to the surface of the headwater pool (depth + velocity head). Water surface and energy line at the entrance are assumed to coincide. 4.8.3.4 Hydraulic Slope The hydraulic slope or hydraulic grade line, sometimes called the pressure line is defined by the elevations to which water would rise in small vertical pipes attached to the culvert wall along its length. (Figure 1-42 ) The energy line and the pressure line are parallel over the length of the barrel except in the vicinity of 2 the inlet where the flow contracts and re-expands (Figure 1-4-5 ). The difference is the velocity head, V . ------2g © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-31 Roadway and Ballast 4.8.3.5 Head (H) The head (Figure 1-4-5) or energy required to pass a given quantity of water through a culvert flowing in outlet 2 V , and entrance loss He, and a friction loss Hf. This control (with barrel full) is made up of velocity head H v = -----2g energy is obtained from ponding at entrance and slope of pipe, and is expressed in equation form: EQ 4-2 H = Hv + He + Hf 4.8.3.6 Entrance Loss (He) Entrance Loss depends upon the geometry of the inlet edge. This loss is expressed as a coefficient ke multiplied by the barrel velocity head or 2 V H e = k e ------2g EQ 4-3 Figure 1-4-3. Relationship of Headwater to High Tailwater and Other Terms in EQ 4-1 Figure 1-4-4. Low Tailwater in Relation to Terms of the Flow Equation © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-32 AREMA Manual for Railway Engineering Culverts Figure 1-4-5. Difference Between Energy Grade Line and Hydraulic Grade Line 1 4.8.3.7 Friction Loss (Hf) a. Friction loss is the energy required to overcome the roughness of the culvert barrel and is expressed in the following equation: 2 2 29n L V H f = ------------------------------------ R 1.33 2g EQ 4-4 3 where: n = Manning’s friction factor. See Table 1-4-15 and Table 1-4-16 4 L = length of culvert barrel, ft V = mean velocity of flow in barrel, ft/sec g = acceleration of gravity, 32.2, ft/sec2 A R = hydraulic radius, or ---------- ft WP WP = wetted perimeter, ft b. Substituting in EQ 4-2 and simplifying (for Bernoulli’s Theorem) we get for full flow: 2 2 n L V H = l + k e + 29 --------------------- ------1.33 2g R c. EQ 4-5 Nomographs for solving EQ 4-5 are shown in Reference 22. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-33 Roadway and Ballast 4.8.4 HYDRAULIC COMPUTATIONS (1989) a. Following the balanced design approach, establish the minimum opening required to pass the 25-year flood with no ponding. b. From the hydrology data the 25-year discharge has been established. The pipe size to carry this flow with no head at the entrance, HW/D = 1.0, is determined from the charts. Using the 25-year discharge, determine the pipe size required for both inlet and outlet control and use whichever is greater. This is the minimum size opening required in the culvert. c. Inlet Control. From Figure 1-4-6 through Figure 1-4-12 the headwater for a given pipe can be determined. Using the minimum size selected for the 25-year flood, determine the headwater (for the entrance condition desired) for the 100-year flood discharge. If this amount of headwater is acceptable for the culvert in question, the minimum size is satisfactory for the full 100-year design discharged in inlet control. If the headwater is too high, a larger size must be selected corresponding to the maximum permissible headwater. Now check for possible outlet control, as follows. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-34 AREMA Manual for Railway Engineering 1-4-34 Table 1-4-15. Values of Coefficient of Roughness (n) for Standard Corrugated Metal Pipe (Manning’s Formula) (Reference 1) Flowing: Diameters 8 in. Full Unpaved Full 25% Paved Part Full Paved 0.024 0.021 0.027 Flowing: Pipe Arch 10 in. 12 in. 15 in. 18 in. 24 in. 30 in. 36 in. 42 in. 48 in. 54 in. and Larger 0.012 0.014 0.011 0.012 0.013 0.015 0.017 0.018 0.019 0.020 0.021 0.014 0.016 0.017 0.018 0.020 0.019 0.012 0.013 0.015 0.017 0.019 0.020 0.021 0.022 0.023 17×13 21×15 28×20 35×24 42×29 49×33 57×38 64 × 43 in. and Larger Full Unpaved 0.026 Part Full Unpaved 0.029 Annular 2-2/3 × 1/2 in. 0.013 0.014 0.016 0.018 0.019 0.020 0.021 0.022 0.018 0.019 0.021 0.023 0.024 0.025 0.025 0.026 Helical – 3 × 1 in. Flowing: 3 × 1 in 36 in. 42 in. 48 in. 54 in. 60 in. 66 in. 72 in. 78 in. & larger Full Unpaved Full 25% Paved 0.027 0.023 0.022 0.022 0.023 0.023 0.024 0.025 0.026 0.019 0.019 0.020 0.020 0.021 0.022 0.022 Flowing: Annular 5 × 1 in. Full Unpaved Full 25% Paved 0.025 0.022 0.027 0.023 Helical – 5 × 1 in. 48 in. 54 in. 60 in. 66 in. 72 in. 78 in. & Larger 0.022 0.022 0.023 0.024 0.024 0.019 0.019 0.020 0.021 0.021 0.025 0.022 All pipe with smooth interior* All Diameters 0.012 *Includes full paved pipe, concrete lined pipe and spiral ribbed pipe. Table 1-4-16. Values of n for Structural Plate Pipe for 6 ″ × 2 ″ Corrugations (Manning’s Formula) (Reference 25) Corrugations 6″ × 2″ Plain – unpaved 25% Paved Diameters 5 ft 7 ft 10 ft 15 ft 0.033 0.028 0.032 0.027 0.030 0.026 0.028 0.024 Culverts AREMA Manual for Railway Engineering © 2010, American Railway Engineering and Maintenance-of-Way Association Corrugations Helical Annular 2-2/3 × 1/2 1-1/2 × 1/2 in. in. Roadway and Ballast NOTE: The manufacturers recommended keeping HW/D to a maximum of 1.5 and preferably to no more than 1.0. Figure 1-4-6. Inlet Control – Headwater Depths for Corrugated Metal Pipe Culverts © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-36 AREMA Manual for Railway Engineering Culverts 1 3 4 NOTE: Headwater depth should be kept low because pipe arches are generally used where headroom is limited. Figure 1-4-7. Inlet Control – Headwater Depths for Corrugated Metal Pipe-arch Culverts © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-37 Roadway and Ballast Figure 1-4-8. Inlet Control – Headwater Depths for Structural Plate Pipe-arch Culverts with 18-inch Radius Corner Plate for Three Types of Inlet (Reference 22) © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-38 AREMA Manual for Railway Engineering Culverts 1 3 4 Figure 1-4-9. Inlet Control – Headwater Depths for Structural Plate Pipe-arch Culverts with 31-inch Radius Corner Plate for Three Types of Inlet (Reference 22) © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-39 Roadway and Ballast Figure 1-4-10. Inlet Control – Headwater Depths for Concrete Pipe Culverts for Three Types of Inlet (Reference 22) © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-40 AREMA Manual for Railway Engineering Culverts 1 3 4 Figure 1-4-11. Inlet Control – Headwater Depths for Oval Concrete with Long Axis Horizontal for Three Types of Inlet (Reference 22) © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-41 Roadway and Ballast Figure 1-4-12. Inlet Control – Headwater Depths for Oval Concrete Pipe Culverts with Long Axis Vertical for Three Types of Inlet (Reference 22) © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-42 AREMA Manual for Railway Engineering Culverts d. Outlet Control. Using the size selected for inlet control use Figure 1-4-13 through Figure 1-4-18 to determine the headwater depth in outlet control. If the depth here is greater than that for inlet control, the culvert is assumed to be in outlet control and the higher depth applies. e. Wall roughness factors used are stated on the flow charts (Table 1-4-17 through Table 1-4-19). For other values of n, use an adjusted value for length, L ´, on the length scales on the charts. L ´ is calculated by the formula: n 2 L = L ----- n EQ 4-6 where: L = Actual length n´ = Actual value of Manning’s n n = Value of Manning’s n shown on chart. f. Using L´ on the length scales in the charts, adjust the result for the Manning’s n desired. g. The appropriate k curve is selected for the entrance condition desired. Typical values of k are found in e e Table 1-4-14. h. If the culvert is in outlet control and the headwater exceeds the allowable, a larger size can be selected corresponding to acceptable headwater depth. In such a case, alternate solutions should be considered for corrugated steel structures with lower roughness coefficients. See Table 1-4-15. A smaller size of paved pipe or helical pipe may be satisfactory. i. Entrance conditions should also be considered. It may be economical to use a more efficient entrance than planned if a size difference results. Check the lowest ke curve results. j. For graphed hydraulic elements and properties of circular corrugated steel pipe and corrugated steel and structural plate pipe-arches refer to Figure 1-4-19 and Figure 1-4-20. 1 3 k. For full-flow data refer to Table 1-4-20 through Table 1-4-23. l. For a comparison of waterway cross-sectional areas at equal depths of flow in circular pipe and pipe-arch refer to Figure 1-4-21. Note that the pipe-arch handles a larger volume at the lower levels of flow. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-43 4 Roadway and Ballast Figure 1-4-13. Outlet Control – Head for Corrugated Metal Pipe Culvert with Submerged Outlet and Culvert Flowing Full (See Note Under Sketch at Top) (Reference 22) Table 1-4-17. Length Adjustment for Improved Hydraulics Pipe Diameter Inches Roughness Factor n´ for Helical Corrugations (Note 1) 12 24 36 48 0.011 0.016 0.019 0.020 Length Adjustment Factor 2 n --- n 0.21 0.44 0.61 0.70 Note 1: Other values of roughness, n, are applicable to paved pipe, lined pipe and pipe with 3 1 inch corrugations. See Table 1-4-15. To use the above chart for these types of pipe and pipe arches, use adjusted length factors computed per EQ 4-6. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-44 AREMA Manual for Railway Engineering Culverts 1 3 4 Figure 1-4-14. Outlet Control – Head for Corrugated Metal Pipe-arch Culvert with Submerged Outlet and Flowing Full (Reference 22) (For length adjustment see Table 1-4-17 on Page 1-4-44.) © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-45 Roadway and Ballast Figure 1-4-15. Outlet Control – Head for Structural Plate Pipe Culvert with Submerged Outlet and Flowing Full (Reference 22) Table 1-4-18. Length Adjustment for Improved Hydraulics Roughness Factor Pipe Diameter, ft 5 7 10 15 Curves Based on Actual n´ = (Note 1) n= 0.0328 0.0320 0.0311 0.0302 0.033 0.032 0.030 0.028 Length Adjustment Factor 2 n --- n 1.0 1.0 0.93 0.86 Note 1: See Table 1-4-15. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-46 AREMA Manual for Railway Engineering Culverts 1 3 NOTE: For 31-inch corner radius use structure sizes with equivalent areas on the 18-inch corner radius scale. Figure 1-4-16. Outlet Control – Head for Structural Plate Pipe-arch Culvert with 18 -Inch Corner Radius with Submerged Outlet and Flowing Full (Reference 22) Table 1-4-19. Length Adjustments for Improved Hydraulics Roughness Factor Pipe Arch Size, ft Curves based on n Actual n´ (Note 1) 6.1 4.6 8.1 5.8 11.4 7.2 16.610.1 0.0327 0.0321 0.0315 0.0306 0.0327 0.032 0.030 0.028 Length Adjustment Factor 2 n --- n 1.0 1.0 0.907 0.837 Note 1: See Table 1-4-16. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-47 4 Roadway and Ballast Figure 1-4-17. Outlet Control – Head for Concrete Pipe Culverts with Submerged Outlet and Flowing Full (Reference 22) © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-48 AREMA Manual for Railway Engineering Culverts 1 3 4 Figure 1-4-18. Outlet Control – Head for Oval Concrete Pipe Culverts with Long Axis Horizontal or Vertical Submerged Outlet and Flowing Full (Reference 22) © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-49 Roadway and Ballast Figure 1-4-19. Hydraulic Elements for Circular Corrugated Steel Pipe © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-50 AREMA Manual for Railway Engineering Culverts Table 1-4-20. Full Flow Data for Round Pipe Diameter, in. Area, ft2 Hydraulic Radius, ft Diameter, in. Area, ft2 Hydraulic Radius, ft 12 0.785 0.250 156 132.7 3.25 15 1.227 0.3125 162 143.1 3.375 18 1.767 0.375 168 153.9 3.5 21 2.405 0.437 174 165.1 3.625 24 3.142 0.50 180 176.7 3.75 30 4.909 0.625 186 188.7 3.875 36 7.069 0.75 192 201.1 4.0 42 9.621 0.875 198 213.8 4.125 48 12.566 1.0 204 227.0 4.25 54 15.904 1.125 210 240.5 4.375 60 19.635 1.25 216 254.5 4.5 66 23.758 1.375 222 268.8 4.625 72 28.27 1.5 228 283.5 4.75 78 33.18 1.625 234 298.6 4.875 84 38.49 1.75 240 314.2 5.0 90 44.18 1.875 246 330.1 5.125 96 50.27 2.0 252 346.4 5.25 108 63.62 2.25 258 363.1 5.375 114 70.88 2.375 264 380.1 5.5 120 78.54 2.5 270 397.6 5.625 126 86.59 2.625 276 415.5 5.75 132 95.03 2.75 282 433.7 5.875 138 103.87 2.875 288 452.4 6.0 144 113.10 3.00 294 471.4 6.125 150 122.7 3.125 300 490.9 6.25 1 3 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-51 Roadway and Ballast Figure 1-4-20. Hydraulic Properties of Corrugated Steel and Structural Plate Pipe-arches Table 1-4-21. Full Flow Data for Corrugated Steel Pipe-arches Corrugations 2-2/3" x 1/2" Dimensions, in. Pipe-arch Waterway Area, ft2 Corrugations 3" x 1" and 5" x 1" Hydraulic Radius Diameter, A/D, in. ft Equiv. Size, in. Waterway Area, ft2 Hydraulic Radius A/D, ft Pipe Diameter Span Rise 15 17 13 1.1 0.280 54 60 46 15.6 1.104 18 21 15 1.6 0.340 60 66 51 19.3 1.230 21 24 18 2.2 0.400 66 73 55 23.2 1.343 24 28 20 2.9 0.462 72 81 59 27.4 1.454 30 35 24 4.5 0.573 78 87 63 32.1 1.573 36 42 29 6.5 0.69 84 95 67 37.0 1.683 42 49 33 8.9 0.81 90 103 71 42.4 1.80 48 57 38 11.6 0.924 96 112 75 48.0 1.911 54 64 43 14.7 1.04 102 117 79 54.2 2.031 60 71 47 18.1 1.153 108 128 83 60.5 2.141 66 77 52 21.9 1.268 114 137 87 67.4 2.259 72 83 57 26.0 1.38 120 142 91 745 2.373 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-52 AREMA Manual for Railway Engineering Culverts Table 1-4-22. Full Flow Data for Structural Plate Pipe-arches – Corrugations 6 2 Corner Plates 9 pi Dimensions, ft-in. Radius (Rc) = 18 in. Waterway Area, ft2 Hydraulic Radius, ft Span Rise 6-1 4-7 22 1.29 6-4 4-9 24 1.35 6-9 4-11 26 1.39 7-0 5-1 28 1.45 7-3 5-3 30 1.51 7-8 5-5 33 1.55 7-11 5-7 35 1.61 8-2 5-9 38 1.67 8-7 5-11 40 1.71 8-10 6-1 43 1.77 9-4 6-3 45 1.81 9-6 6-5 48 1.87 9-9 6-7 51 1.93 10-3 6-9 54 1.97 10-8 6-11 57 2.01 10-11 7-1 60 2.07 11-5 7-3 63 2.11 11-7 7-5 66 2.17 11-10 7-7 70 2.23 12-4 7-9 73 2.26 12-6 7-11 77 2.32 12-8 8-1 81 2.38 12-10 8-4 85 2.44 13-5 8-5 88 2.48 13-11 8-7 91 2.52 14-1 8-9 95 2.57 14-3 8-11 100 2.63 14-10 9-1 103 2.67 15-4 9-3 107 2.71 15-6 9-5 111 2.77 15-8 9-7 116 2.83 15-10 9-10 121 2.89 16-5 9-11 125 2.92 16-7 10-1 130 2.98 1 3 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-53 Roadway and Ballast Table 1-4-23. Full Flow Data for Corrugated Steel Pipe-arches – Corrugations 6 2 Corner Plates 15 pi Radius (Rc) = 31 in. Rise, ft-in. Area, ft2 Hydraulic Radius, ft 13-3 9-4 97 2.68 13-6 9-6 102 2.74 14-0 9-8 105 2.78 14-2 9-10 109 2.83 Span, ft-in. 14-5 10-0 114 2.90 14-11 10-2 118 2.94 15-4 10-4 123 2.98 15-7 10-6 127 3.04 15-10 10-8 132 3.10 16-3 10-10 137 3.14 16-6 11-0 142 3.20 17-0 11-2 146 3.24 17-2 11-4 151 3.30 17-5 11-6 157 3.36 17-11 11-8 161 3.40 18-1 11-10 167 3.45 18-7 12-0 172 3.50 18-9 12-2 177 3.56 19-3 12-4 182 3.59 19-6 12-6 188 3.65 19-8 12-8 194 3.71 19-11 12-10 200 3.77 20-5 13-0 205 3.81 20-7 13-2 211 3.87 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-54 AREMA Manual for Railway Engineering Culverts 1 NOTE: The pipe arch handles a larger volume at the lower levels of flow. 3 Figure 1-4-21. Comparison of Waterway Cross-sectional Areas at Equal Depths of Flow in Circular Pipe and Pipe-arch 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-55 Roadway and Ballast SECTION 4.9 DESIGN CRITERIA FOR CORRUGATED METAL PIPES 4.9.1 CRITERIA (1994) Four criteria must be considered in the structure design of a flexible buried conduit. The criteria are seam strength, flexibility factor, wall area and buckling. 4.9.2 FORMULAS (1994) 4.9.2.1 Seam Strength a. Seam strength shall be sufficient to develop the compressive thrust in the pipe wall. This compressive thrust (T) in lb per lineal foot of structure is: S T = LL + DL --2 EQ 4-7 EQ 4-8 C = T(S.F.) = Compressive thrust with safety factor where: LL = Design Live Load (psf) (See Article 4.9.3.b) DL = Dead Load (psf) (See Article 4.9.3.a) S = Span (ft) (Max dia of pipe) SF = Safety Factor. Recommend SF = 3 b. The value for C should not exceed values shown in Article 4.9.4c, Table 1-4-27. 4.9.2.2 Handling and Installation Strength a. Handling and installation rigidity is measured by a Flexibility Factor (F.F.) determined by the formula: FF = S2/EI EQ 4-9 where: FF = Flexibility Factor in inches per pound. S = Max. span in inches E = Modulus of elasticity of the pipe material (psi) (See Table 1-4-26) I = Moment of inertia per unit length of cross section of the pipe (inches to 4th power per inch) (See Table 1-4-28) b. FF shall not exceed 0.043 for 2inch depth corrugation; 0.033 for 1 inch depth corrugation. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-56 AREMA Manual for Railway Engineering Culverts 4.9.2.3 Wall Area Formula for wall area is: T A = ---fa EQ 4-10 where: A = Required wall area (in.2/ft) (See Table 1-4-28) T = Thrust (lb/ft) (See Article 4.9.2.1) fa = Allowable wall stress = minimum yield point divided by an appropriate safety factor; fy f a = ------EQ 4-11 SF fy = Minimum yield point (psi – see Article 4.9.4b, Table 1-4-26) 4.9.2.4 Buckling Corrugations with the required wall area, A, shall be checked for possible buckling. If the allowable buckling stress fcr/SF, is less than fa, the required area must be recalculated using fcr/SF in lieu of fa. Formulae for buckling are: f 2 r 24E u KS 2 if S < ---- ----------- then f cr = f u – ---------- -------48E r K fu r if S > ---K 24E 12E ----------- then f cr = -----------------fu KS - 2 ------r 1 EQ 4-12 EQ 4-13 3 where: fcr = critical buckling stress (psi) S = max, span in inches 4 r = Radius of gyration in inches (See Table 1-4-28) E = Modulus of elasticity (psi) (See Article 4.9.4b) Table 1-4-26 K = Soil stiffness factor (See below) SF = Safety factor (Recommend SF = 2) fu = Minimum tensile strength (psi) (See Article 4.9.4.b) (See Table 1-4-26) Soil stiffness factor = 0.22 for 95% compaction 0.33 for 90% compaction 0.44 for 85% compaction 4.9.3 LOADS (1994) a. Dead load = 120 lb per cubic foot height of cover in feet. b. Live loads, including 50% impact, for Cooper E-80 as shown in Table 1-4-24. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-57 Roadway and Ballast Table 1-4-24. Live Loads for Cooper E-80 Height of cover (ft) Live Load lb/sq ft Height of Cover (ft) Live Load lb/sq ft 2 3800 12 800 5 2400 15 600 8 1600 20 300 10 1100 30 100 4.9.4 PIPE CULVERT DESIGN PROPERTIES (1989) a. Gage vs metal thickness in inches to be used in design of pipe culverts are shown in Table 1-4-25. b. Mechanical properties of metal to be used in design of pipe culverts are shown in Table 1-4-26. c. Seam strength of riveted pipe culverts are shown in Table 1-4-27. d. Section properties of corrugated metals are shown in Table 1-4-28. Table 1-4-25. Gage vs Metal Thickness Steel Aluminum Specified Thickness Specified Thickness 16 0.064 0.060 14 0.079 0.075 12 0.109 0.105 10 0.138 0.135 8 0.168 0.164 Gage Table 1-4-26. Metal Mechanical Properties Minimum Tensile Strength (psi) Minimum Yield Point (psi) Mod of Elasticity psi Steel 45000 33000 29106 Aluminum 31000 24000 10106 Metal © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-58 AREMA Manual for Railway Engineering Culverts Table 1-4-27. Minimum Longitudinal Seam Strength in Kips per Foot Corrugation 2-2/3 x 1/2 and 2 x 1/2 Gage Single Rivet k/ft Double Rivet k/ft 3x1 6x1 Double Rivet k/ft Double Rivet k/ft Riveted Steel Pipe 16 16.7 21.6 28.7 – 14 18.2 29.8 35.7 – 12 23.4 46.8 53.0 – 10 24.5 49.0 63.7 – 8 25.6 51.3 70.7 – Riveted Aluminum Pipe 16 9.0 14.0 16.5 16.0 14 9.0 18.0 20.5 19.9 12 15.6 31.5 28.0 27.9 10 16.2 33.0 42.0 35.9 8 16.8 34.0 54.5 43.5 1 Table 1-4-28. Steel and Aluminum Corrugated Pipes Corrugation 2-2/31/2 A r I 10–3 A r I 10–3 A r I 10–3 in 2 --------ft in. in 4 --------ft in 2 --------ft in. in 4 --------ft in 2 --------ft in. in 4 --------ft 16 0.755 .1712 1.89 0.890 .3417 8.66 0.794 .3657 8.85 14 0.968 .1721 2.39 1.113 .3427 10.89 0.992 .3663 11.09 12 1.356 .1741 3.43 1.560 .3448 15.46 1.390 .3677 15.65 10 1.744 .1766 4.53 2.008 .3472 20.18 1.788 .3693 20.32 8 2.133 .1795 5.73 2.458 .3499 25.09 2.186 .3711 25.09 Gage 3 5 1 (Note 1) 31 4 Note 1: Not applicable for aluminum corrugated pipes © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-59 Roadway and Ballast 4.9.5 MINIMUM AND MAXIMUM HEIGHT OF COVER IN FEET (1989) Minimum and maximum height of cover for various thickness (gage) of metal are given in Table 1-4-29 for Steel Round Pipe and in Table 1-4-30 for Aluminum Round Pipe. The design criteria used in development of Table 1-429 and Table 1-4-30 are as follows: 4.9.5.1 Safety Factors SF = 3.0 for longitudinal seams SF = 2.0 for pipe wall buckling SF = 2.0 for wall area FF = 0.043 for 2 depth corrugation and 0.033 for 1 depth corrugation. 4.9.5.2 Design Factors • Dead load pressure = 120 psf per foot of height. • Live load pressure = As shown in Table 1-4-24 for Cooper E-80 Live Load plus 50% of the live load for impact. • Seam strengths, modulus of elasticity, tensile strength. • Yield point, etc., used are as shown in Tables. • Soil stiffness coefficient “K” = 0.33 for 90% compaction based on ASTM D698. • These tables are based on structural considerations. Abrasive or corrosive conditions at the site may require a greater sheet thickness or protective coating and invert paving. • Maximum height of cover may be controlled by maximum head water depth. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-60 AREMA Manual for Railway Engineering Culverts Table 1-4-29. Steel Round Corrugated Pipe Minimum and Maximum Height of Cover in Feet Sheet Thickness Pipe Dia. Ins. (Inch and Gage) 2-2/3 x 1/2 and 2 x 1/2 in. Corrugation 0.064 16 ga 0.079 14 ga 0.109 12 ga 12 1-1/2-90 1-1/2-100 15 1-1/2-70 1-1/2-80 18 1-1/2-60 1-1/2-65 1-1/2-85 21 1-1/2-50 1-1/2-55 1-1/2-70 24 1-1/2-45 1-1/2-50 1-1/2-65 30 2-35 36 3-30 42 2-30 48 3-30 0.138 10 ga 0.168 8 ga 5 x 1 or 3 x 1 in. Corrugation 0.064 16 ga 0.079 14 ga 0.109 12 ga 0.138 10 ga 0.068 8 ga 1-1/2-40 1-1/2-50 2-30 1-1/2-40 1-1/2-45 1-1/2-45 1-1/2-70 1-1/2-73 1-1/2-80 2-40 2-65 2-65 2-70 2-35 2-55 2-60 2-60 2-35 2-50 2-50 2-55 3-30 2-35 2-55 2-70 2-75 66 2-45 2-50 3-25 2-35 2-50 2-60 2-70 72 2-45 2-45 4-25 3-30 2-45 2-55 2-65 2-40 6-20 3-30 2-45 2-50 2-60 7-20 4-25 2-40 2-50 2-55 90 4-25 2-35 2-45 2-50 96 7-20 2-35 2-40 2-45 102 7-20 3-30 3-40 3-45 108 3-30 3-35 3-40 114 3-30 3-35 3-40 120 3-25 3-35 3-35 54 60 78 84 1-1/2-40 1-1/2-45 1-1/2-70 1-1/2-85 1-1/2-95 1-1/2-40 1-1/2-65 1-1/2-75 1-1/2-85 Note 1: All 42 inches in diameter and larger and all 1 inches depth corrugation shall be double riveted or equal. Note 2: Height of cover is measured from base of cross tie to top of pipe. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-61 1 3 4 Roadway and Ballast Table 1-4-30. Aluminum Round Corrugated Pipe Minimum and Maximum Height of Cover in Feet Sheet Thickness and Gage Pipe Diameter Ins. 2-2/3 x 1/2 and 2 x 1/2 in. Corrugation 0.060 16 ga 0.075 14 ga 12 1-1/2-50 1-1/2-50 15 1-1/2-40 1-1/2-40 0.105 12 ga 0.135 10 ga 18 3-30 3-30 1-1/2-55 21 4-25 4-25 1-1/2-45 24 5-25 5-25 1-1/2-40 1-1/2-45 0.164 8 ga 3 x 1 in. Corrugation 0.060 16 ga 30 2-30 2-35 36 3-25 3-30 3-30 42 1-1/2-50 5-25 48 1-1/2-40 1-1/2-45 0.075 14 ga 0.105 12 ga 0.135 10 ga 1-1/2-35 1-1/2-50 1-1/2-75 3-30 0.164 8 ga 1-1/2100 1-1/2-40 1-1/2-65 1-1/2-85 4-25 2-35 2-55 2-75 5-25 2-30 2-50 2-65 60 3-30 2-45 2-60 66 4-25 2-40 2-55 72 2-35 2-50 78 2-35 2-45 54 84 3-40 90 3-40 Note 1: All 42 inches and larger and all 1 inches depth corrugation shall be double riveted or equal. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-62 AREMA Manual for Railway Engineering Culverts 4.9.6 PIPE ARCHES (1989) 4.9.6.1 Calculations Pipe arches are structurally calculated by same method as standard round pipe, but the maximum soil bearing pressures at the small radius corners must be considered. The design must state the type of backfill materials required around the small radius corners. 4.9.6.2 Corner Pressures Formula Pc = PvRt/Rc EQ 4-14 where: Pc = Pressure acting on soil at small radius corners (lb/ft2) Pv = Design Pressure (lb/ft2) Rt = Radius at crown (ft) Rc = Radius at corner or small radius (ft) Some typical allowable bearing pressures for various backfill materials are given in Table 1-4-31. The values of allowable bearing pressures of backfill material shown in Table 1-4-31 are for preliminary design purposes only, and allowable bearing pressure of actual used backfill material should be tested to ensure it is equal to the design pressure. 1 Table 1-4-31. Typical Allowable Bearing Pressures (See Note 1) Class of Material Allowable Design Bearing Pressure Concrete (3 sacks per cu, yd) 25 TSF (Note 2) Cement treated sand and gravel 20 TSF (Note 2) Compacted gravel or sand and gravel 6 TSF (Note 2) Loose gravel or compacted coarse sand 4 TSF (Note 2) Loose coarse sand or gravel and sand 3 TSF (Note 2) Loose fine sand 2 TSF (Note 2) Medium stiff clay 22 TSF (Note 2) Medium soft clay 12 TSF (Note 2) Silt and very fine sand 2 TSF (Note 2) Swamp material (muck, peat, etc.) 0 TSF (Note 2) 3 4 Note 1: To be used only for design purpose (See Article 4.9.6.2) Note 2: Tons per square foot © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-63 Roadway and Ballast 4.9.6.3 Minimum and Maximum Height of Cover for Arch Pipes Minimum height of cover for 2-2/31/2, 51 or 31 corrugation shall not be less than 2 feet nor less than the span. Maximum height of cover shall not be greater than 30 feet (Height of cover is measured from base of cross-tie to top of arch pipe) (Table 1-4-32). Table 1-4-32. Steel and Aluminum Arch Pipes Minimum Thickness of Metal (Gage) Minimum Thickness of Metal (Gage) Equiv. Pipe Diameter Inches Span Rise (Inches) 15 17 13 0.079 (14 ga) 0.135 (10 ga) 18 21 15 0.079 (14 ga) 0.135 (10 ga) 21 24 18 0.079 (14 ga) 0.135 (10 ga) 24 28 20 0.079 (14 ga) 0.135 (10 ga) 30 35 24 0.109 (14 ga) 0.135 (10 ga) 36 42 29 0.138 (10 ga) 0.164 (8 ga) 42 49 33 48 2-2/3 x 1/2 in. Corrugation Steel Aluminum 5 x 1 or 3 x 1 in. Corrugation Steel Aluminum 0.064 (16 ga) 0.105 (12 ga) 0.109 (12 ga) 0.064 (16 ga) 0.105 (12 ga) 57 37 0.138 (10 ga) 0.079 (14 ga) 0.135 (10 ga) 54 64 43 0.138 (10 ga) 0.079 (14 ga) 0.135 (10 ga) 60 71 47 0.138 (10 ga) 0.109 (12 ga) 0.135 (10 ga) 66 77 52 0.138 (10 ga) 0.109 (12 ga) 0.135 (10 ga) 72 81 59 0.109 (12 ga) 0.135 (10 ga) 78 87 63 0.109 (12 ga) 0.164 (8 ga) 84 95 67 0.109 (12 ga) 90 103 71 0.109 (12 ga) 96 112 75 0.138 (10 ga) 102 117 79 0.138 (10 ga) 108 128 83 0.168 (8 ga) 114 13787 0.168 (8 ga) Note 1: Arch pipes 42 and larger and all 1 depth corrugation shall be double riveted or equal. Note 2: Soil bearing pressures at corners must be determined. See Article 4.9.6.2 Note 3: In weak bearing soils, a larger diameter round pipe may be required and partly buried to obtain minimum cover, but the same rise and area of the proposed pipe arch should be maintained. Another method is to replace the weak bearing soils with a high bearing value material for a distance great enough so that the high corner pressures no longer has an adverse effect. (See Article 4.9.6.2 for requirements). © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-64 AREMA Manual for Railway Engineering Culverts SECTION 4.10 DESIGN CRITERIA FOR STRUCTURAL PLATE PIPES 4.10.1 CRITERIA FORMULAS (1989) a. Four criteria shall be considered in the design of structural plate pipe culverts, which are the same as stated in Article 4.9.1. b. Formulas given under Article 4.9.2 shall be used in the design of structural plate culvert pipes. Table 1-4-24 and Table 1-4-26 may be used, but all other properties needed for solving the formulas are furnished in Table 1-4-33 and Table 1-4-34. c. Recommended safety factors are given for each formula under Article 4.9.2, except that flexibility factor shall not exceed 0.02 for round pipe, 0.03 for arch pipes and 0.03 for arches. 4.10.2 SEAM STRENGTH OF STRUCTURAL PLATE PIPES (1989) Minimum longitudinal seam strength in kips per foot are shown in Table 1-4-33 and section properties in Table 1-4-34. Table 1-4-33. Steel and Aluminum Structural Plate Pipes in Kips per Foot all Bolts to be 3/4 inch in Size Thickness Gage 12 10 8 7 5 3 1 Steel Inches Aluminum Inches 4 0.109 0.138 0.168 0.188 0.218 0.249 0.280 0.10 0.125 0.15 0.175 0.20 0.225 0.250 43 62 81 93 112 132 144 62 Steel 92-1/2 Aluminum Bolts Per Foot Steel Bolts Aluminum Bolts 5-1/3 Per Foot 5-1/3 Per Foot 6 180 8 28. 41. 54.1 63.7 73.4 83.2 93.1 194 26.4 34.8 44.4 52.8 52.8 52.8 52.8 3 4 Table 1-4-34. Steel and Aluminum Structural Plate Pipes Section Properties 62 Steel 92-1/2Aluminum Gage A (inch2/ft) r (inch) I 10–3 inch4/inch A inch2/foot r inch I 10–3 inch4/inch 12 10 8 7 5 3 1 1.556 2.003 2.449 2.739 3.199 3.650 4.119 0.682 0.684 0.686 0.688 0.690 0.692 0.695 60.411 78.175 96.163 108.000 126.922 146.172 165.836 1.404 1.750 2.100 2.449 2.799 3.149 3.501 0.8438 0.8444 0.8449 0.8454 0.8460 0.8469 0.8473 83.065 103.991 124.883 145.895 166.959 188.179 209.434 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1 1-4-65 Roadway and Ballast 4.10.3 MINIMUM AND MAXIMUM HEIGHT OF COVER IN FEET (1989) a. Minimum and maximum height of cover measured from base of ties to top of pipe for various thickness (gage) of metal are given in Table 1-4-35 for steel and Table 1-4-36 for aluminum structural plate pipes using steel bolts and Table 1-4-37 using aluminum bolts. Minimum height of cover shall not be less than 2 feet nor less than one fourth the maximum span. Greater cover for protection from heavy equipment may be needed during construction. b. Safety Factors used in Table 1-4-35, Table 1-4-36 and Table 1-4-37 are as follows: Longitudinal Seams. . . . . . . . . . . . . . . . . . . 3 Wall Buckling. . . . . . . . . . . . . . . . . . . . . . . . 2 Wall Area . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Flexibility Factor . . . . . . . . . . . . . . . . . . . . . 0.02 Dead Load Pressure . . . . . . . . . . . . . . . . . . 120 psf of height Live Load E-80 plus 50% for impact. . . . . . Soil Stiffness Coefficient “K” . . . . . . . . . . . = 0.33 for 90% compaction base on ASTM D-698 c. The tables are based on structural considerations. Abrasive or corrosive conditions at the site may require a greater thickness in the bottom plates. Table 1-4-35. Steel Round Structural Plate Pipe Minimum and Maximum Height of Cover (ft) 4 Bolts per Foot Span (ft) 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 6 Bolts/ft 8 Bolts/ft Plate Thickness inches and gage 0.109 12 ga 0.138 10 ga 0.168 8 ga 0.188 7 ga 0.218 5 ga 0.243 3 ga 0.280 1 ga 0.280 1 ga 0.280 1 ga 3-30 4-25 6-20 2-40 3-35 3-30 3-30 4-25 2-55 3-50 3-45 3-40 3-35 2-60 3-55 3-50 3-45 3-40 2-75 3-65 3-60 3-55 3-50 2-90 3-80 3-70 3-65 3-60 2-100 3-85 3-80 3-70 3-65 2-125 3-110 3-100 3-90 3-80 2-130 3-120 3-105 3-95 3-90 4-25 6-20 7-20 8-20 4-30 4-30 4-30 4-25 5-25 4-40 4-35 4-30 4-30 5-30 5-25 4-45 4-40 4-40 4-35 5-35 5-30 4-55 4-50 4-45 4-45 5-40 5-40 5-35 5-35 6-30 4-60 4-55 4-50 4-50 5-45 5-40 5-40 5-40 6-35 6-30 4-75 4-70 4-65 4-60 5-55 5-45 5-45 5-40 6-35 6-30 6-30 6-30 6-20 4-80 4-75 4-70 4-65 5-60 5-45 5-45 5-40 6-35 6-30 6-30 6-30 6-20 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-66 AREMA Manual for Railway Engineering Culverts Table 1-4-36. Aluminum Round Structural Plate Pipe Minimum and Maximum Height of Cover (ft) Steel Bolts 5-1/3 Bolts Per Foot Span (ft) Plate Thickness and Gage 0.100 12 ga 0.125 10 ga 0.150 8 ga 0.175 7 ga 0.200 5 ga 0.225 3 ga 0.250 1 ga 6 6-25 3-35 2-50 2-55 2-65 2-75 2-85 7 8-20 3-30 2-40 2-50 2-55 2-65 2-70 8 4-25 2-35 2-40 2-50 2-55 2-60 9 5-25 3-30 3-35 3-45 3-50 3-55 10 7-20 3-30 3-35 3-35 3-45 3-50 11 4-25 3-30 3-35 3-40 3-45 12 5-25 3-25 3-30 3-35 3-40 13 7-20 4-25 4-30 4-35 4-40 5-25 4-25 4-30 4-35 4-25 4-30 4-30 4-25 4-30 14 15 16 17 1 5-30 Table 1-4-37. Aluminum Round Structural Plate Pipe Minimum and Maximum Height of Cover (ft) Span (ft) Aluminum Bolts 5-1/3 bolts per foot Plate thickness and gage (Note 1) 0.100 12 ga 0.125 10 ga 0.150 8 ga 0.175 7 ga 6 6-20 3-30 2-40 2-45 7 8-20 4-25 2-35 2-40 8 4-20 2-30 2-35 9 8-20 4-25 3-30 10 6-20 3-25 11 7-20 4-25 12 6-20 13 7-20 14 9-20 15 10-15 3 4 Note 1: Gages 5, 3 and 1 have same strength as gage 7 since bolts control. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-67 Roadway and Ballast SECTION 4.11 CULVERT END TREATMENTS 4.11.1 INTRODUCTION (1992) a. The design and installation of each culvert should be considered as an individual engineering and economic problem. The engineer should determine the basic requirements of type strength, capacity, service, location, alignment, grade, and other factors pertinent to the efficient function and economic installation and maintenance of the culvert. b. In addition, he should decide if the physical conditions, both present and during the projected life of the culvert, warrant the inclusion of headwalls, wingwalls, inverts, and aprons as part of the installation. c. Occasionally, aesthetic considerations may require the use of these appurtenances within built-up communities or in prominent locations where a pleasing appearance is necessary, but normally this is not a major consideration. In most cases it is more expedient to use other and less expensive methods to avoid all or part of these end finishes. For example, except where limited right-of-way makes it necessary to provide headwalls and wingwalls, it is usually more economical to extend pipe culverts. Box and arch culverts, especially when of large capacity, present a somewhat different problem. Again, however, the cost of installation should be carefully compared with other solutions, such as grouted rip-rap, sheet piling, etc., which might provide adequate protection at less cost. 4.11.2 HEADWALLS (1989) 4.11.2.1 Factors and Conditions The following factors and conditions may require the use of headwalls: a. Angle of shearing resistance, type, height, and stability of fill material. b. Inability to hold good vegetation on slopes. c. Prevention of washouts. d. Reduction in cost of culvert by shortening installations. e. Right-of-way limitations. f. Longitudinal stability for short pipe sections to prevent pulling apart. (Only where adequate foundation is available.) g. Improvement of appearance. h. Prevention of undercutting, scour, burrowing and seepage. i. Increase hydraulic efficiency. 4.11.2.2 Design a. Headwalls should be designed by the engineering department, usually the bridge engineers office, and standard design procedures should be followed. b. Economic considerations, based primarily on the required height of the headwall, will determine whether a gravity or reinforced concrete type of structure should be used. The design should provide for all loads, including surcharge and impact, and particular attention should be given to the method used to determine earth thrust. It is very important that the actual soil conditions closely approximate the theoretical conditions assumed in the design. If not, only design methods which through past experience are known to give satisfactory results should be used. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-68 AREMA Manual for Railway Engineering Culverts c. The headwall should have adequate integral strength, and should be proportioned to prevent sliding or overturning from excessive soil pressures. It should be self supporting, and every effort should be made to design against settling. In the case of pipe culverts, this point cannot be overemphasized, as the effectiveness of a carefully located and bedded pipe can be nullified by the settling of an inadequately supported headwall. d. Cut-off walls, where required, should be of sufficient depth to eliminate undercutting. 4.11.3 WINGWALLS (1995) 4.11.3.1 Factors and Conditions The following factors and conditions may require the use of wingwalls: a. Angle of shearing resistance, type, height and stability of fill material. b. Height of culvert. c. Direction, width and gradient of stream channel. d. Amount and velocity of runoff. e. Need for increased hydraulic efficiency. f. Prevention of scour during periods of maximum runoff. 1 4.11.3.2 Design a. Structurally, the same principles govern the design of wingwalls as for headwalls. b. Gravity-type construction is economically desirable for walls of limited height. The walls should be self supporting, and a well reinforced apron, where required, would achieve the desired result. Footing to meet the most adverse conditions encountered should be used, and should be proportioned to provide uniform bearing pressure over the full length of the wingwall. This will assist in preventing separation between the body of the culvert and the wings. c. Perpendicular, oblique, or parallel wingwalls, or a combination thereof, should be used, depending on the physical and hydraulic conditions involved. Careful field engineering is necessary to ascertain that the wingwalls, if skewed, will not change stream direction or encourage turbulence during periods of heavy runoff. d. The height of the culvert and incidence of high water will, to a great extent, govern the length of the wings. Oblique walls are usually tapered from the top of the headwall to a height of approximately 2 feet. Parallel walls may taper their full length to the footing. 4.11.4 INVERTS AND APRONS (1995) 4.11.4.1 Factors and Conditions The following factors and conditions may require the installation of inverts and aprons: a. Prevention of erosion and scour; dispersion of flow. b. Resistance to corrosive and abrasive materials carried by a stream. c. Increased hydraulic efficiency. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-69 3 4 Roadway and Ballast d. Use of culvert as cattle underpass or other purpose, in addition to drainage. 4.11.4.2 Design a. Inverts and aprons should be carefully designed and reinforced, and should be built to carry and control the hydraulic bedload. b. Aprons should be long enough to carry the water well past the toe line at embankments, and should be so designed as to avoid turbulence and eddies. Cut-off walls should be used to prevent undercutting, where necessary. c. Inverts and aprons of culverts handling abrasive and corrosive waters require special care. Those carrying large quantities of abrasive material can be readily protected by properly designed and bonded paving. Mine water, however, particularly from coal, copper and zinc mines, attacks concrete. Water passing through sulfur-bearing rocks or soils and alkaline water have a similar deteriorating effect. Asphaltic or other nonmetallic paving should be considered where corrosive rather than abrasive attack is the governing factor. d. Paving of inverts of culverts to be used as a cattle underpass should be designed to provide reasonably secure footing. Brushed concrete provides an excellent invert if the slope is not excessive. Where this condition exists, cleats may be formed in the concrete to provide additional footing. Bituminous material may also be used as a paving, although small sharp-hoofed livestock will soon cut this type of paving badly, and cause it to deteriorate quickly. SECTION 4.12 ASSEMBLY AND INSTALLATION OF PIPE CULVERTS 4.12.1 GENERAL (1995) a. This portion of the specification presents information pertaining to installation of pipe culverts including alignment; construction methods and procedures; preparation of foundation; unloading and assembly; placement and compaction of backfill; end treatment; and safety provisions. b. This information is not intended to be all inclusive. The user should be aware that pipe manufacturers provide installation instructions pertaining to their individual products. Additionally, industry standards, as well as national specifications, are available to assist the user in proper installation of pipe culverts. Available references for pipe culvert installation are found at the end of this chapter. Also, the reader is referred to Chapter 8, Concrete Structures and Foundations, Part 10, Reinforced Concrete Culvert Pipe, Section 10.4, Installation for further information on the proper installation of concrete culvert pipe. 4.12.2 ALIGNMENT (1995) a. It is important to properly locate the culvert in order to provide the stream with as direct an entrance and exit configuration as possible. Inlet and outlet orientation can be improved by means of a channel change or skewed alignment or a combination of both, Elbows, typically less than 45 degrees, can be installed in the culvert to facilitate alignment changes. However, such alignment changes must be approved by appropriate governing agencies and the railroad Chief Engineer. b. Proper culvert alignment also involves attention to grade line. Culvert grade is essential to the effective and safe functioning of the structure. The ideal grade for a culvert is one which results in neither silting nor in excessive velocities and scour. Culvert line and grade is to be established by the project engineer. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-70 AREMA Manual for Railway Engineering Culverts 4.12.3 CONSTRUCTION METHODS (1995) a. Pipe culvert installation may be by open embankment construction, trench excavation, tunneling, jacking, or a combination of such methods, depending upon site conditions and requirements. b. Trench construction, if done improperly, can be one of the most dangerous situations in construction. In situ soil strength and groundwater elevation must be considered. Consult a qualified geotechnical engineer for design of excavation supports as required. The pipe contractor or railway must strictly conform to all Federal, State and Local regulations and, in particular, the requirements of the Occupational Safety and Health Administration (OSHA). c. Refer to Section 4.13, Earth Boring and Jacking Culvert Pipe through Fills for information on earth boring and jacking culvert pipe. 4.12.4 PREPARATION OF FOUNDATION (1995) a. Pressures caused by both live and dead loads are transmitted from the pipe culvert to the sidefill embankments and the strata underlying the pipe. The supporting soil under the embankments and the pipe must provide required support without excessive settlement. Precautions for soft foundations and for rock strata must be considered if applicable. b. Where the underlying foundation material is unsuitable, this material must be removed and replaced with suitable bedding material placed and compacted to provide a continuous foundation that uniformly supports both the culvert pipe and the sidefill embankments. c. If rock layers are encountered at design culvert invert grade, this rock must be excavated underneath the pipe culvert and replaced with suitable compacted bedding material. The depth of over-excavation required will be dependent upon culvert size and height of cover. However, generally a depth of 12 inches – 24 inches is sufficient. 1 4.12.5 HANDLING AND UNLOADING (1995) a. Pipe shall be shipped and handled in such a manner as to prevent damage to the pipe or to the pipe coating. Pipes shall not be dropped or dragged over the ground. Pipes shall be handled by slings, forks, etc., as required by pipe weight and site conditions. Safety of workers is of paramount importance in all handling operations. Consult with pipe manufacturer regarding specific handling and lifting precautions and requirements. Rough handling is to be avoided. Any damage to coated pipes shall be repaired with an approved field repair method prior to installation. 3 b. Pipe culvert materials must be properly stored if extended time will elapse prior to installation. Pipe coatings or pipe materials affected by UV rays or temperature extremes should be stored under a protective shelter until they can be properly installed. In the case of structural plate culverts, plates should be stored in a manner where moisture will drain rather than collect in the plates. Protected storage is preferred. Stacking plates to provide proper drainage and ventilation helps prevent storage stains. 4 4.12.6 ASSEMBLY (1995) a. Proper assembly of pipe culverts will be dependent upon a number of factors, including the type of culvert pipe material; whether the pipe is factory pipe or field-bolted structural plate pipe; the type of pipe joints; site conditions; etc. b. Joints for pipe culverts can be especially critical depending upon the soil type and conditions, slope of the culvert, infiltration and exfiltration requirements, etc. Field joints must meet the performance criteria established by the project specifications. c. It is not the intention of this text to address the specifics of assembly for all pipe culvert products. Rather, the culvert pipe manufacturers should provide assembly instructions for their products. In addition, the © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-71 Roadway and Ballast reader is referred to the Reference 1, 30, 38, 47, 50, 51 and 52 at the end of this chapter for more detailed information regarding assembly of culvert pipe. 4.12.7 BACKFILL (1995) a. Proper backfill material selection, placement and compaction is essential to the satisfactory performance of pipe culverts. Railroad and highway engineering departments should have established criteria for construction of fill embankments. While such fill requirements may be adequate for pipe culvert installations in general, specific requirements may vary depending on pipe culvert material, size and shape; fill heights and in situ conditions. b. Generally, the selected culvert backfill material should be a well graded granular material, although cohesive materials can be used if careful attention is given to compaction and optimum moisture content. Use of excavated, on site material may be possible provided this material possesses the required engineering properties. The selected fill material must be free from large clods, frozen lumps, rocks, debris and organic material. Extremely fine granular fill may not be suitable due to the possibility of infiltration and piping action. However, use of a filter fabric separator between fill materials of dissimilar size may solve this problem. c. Special care must be taken to provide proper bedding and haunch support for the pipe. See Figure 1-4-22. A relatively loose layer of bedding (generally several inches thick) should be placed under the pipe. However, the fill in the haunch areas is to be carefully compacted to provide support in these critical areas. This is especially important for pipe-arch shapes. d. The selected backfill material should be placed in layers not exceeding 6 inches to 8 inches thickness and compacted to specified density at or near optimum moisture content. Care must be taken to maintain balanced loading on the pipe culvert by keeping the fill level approximately equal on both sides of the pipe at all times. Generally, a compaction density conforming to 90% of ASTM D698 (Standard Proctor) should be adequate. However, individual project specifications will control. e. Flowable fill material such as cement slurry and other controlled low strength materials (CLSM) may be used if economically justifiable. Care must be taken to maintain balanced loading and pressure on the culvert pipe and prevent flotation of the pipe. f. The width of the select fill envelope will be dependent upon site conditions. In narrow trench installation conditions, the select fill must fill the trench from the culvert pipe to the trench wall. Trench width will normally be controlled by the width necessary to install connecting bands or to assemble plates as well as by the width necessary to permit proper placement and compaction of the backfill. Generally a distance of 2 diameter to 1 diameter each side of the pipe is adequate for embankment installations. However, the project engineer must make this determination, taking into account pipe size and shape, height of cover and live load pressures, and in situ soil parameters. g. The select backfill material is to be placed and compacted to a point where minimum cover height above the pipe for anticipated live loads is reached. The remainder of the fill can be standard embankment (or trench) fill meeting the specifications for the given project. h. Compaction of the backfill must be performed in a carefully controlled manner to ensure uniform, dense backfill. Compaction equipment used must not cause distortion to the culvert pipe. Lighter equipment should be used immediately adjacent to the pipe and for the first few lifts above the pipe. i. Proper protection must be provided for anticipated construction loads. Additional fill material — properly placed and compacted — may be needed as a temporary protective pad for heavy equipment loads in excess of design loads for the pipe culvert. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-72 AREMA Manual for Railway Engineering Culverts 1 Figure 1-4-22. Proper Bedding and Haunch Support 3 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-73 Roadway and Ballast 4.12.8 MULTIPLE INSTALLATIONS (1995) When two or more culvert pipes are installed in adjacent, parallel lines, the spacing between the pipes must be adequate to allow proper backfill placement and compaction. This minimum spacing will be dependent upon the shape and size of the pipe culvert, type of end treatment proposed, type of backfill material and type and size of compaction equipment used. Figure 1-4-23 provides some general guidelines. Where the limits on structure spacing are restrictive, the use of flowable fill, CLSM, or low strength portland cement grout, between structures often can reduce the spacing requirements to a practical limit equal to the few inches required for hoses, nozzles, etc., used to place this backfill. Figure 1-4-23. Minimum Permissible Spacings for Multiple Installations 4.12.9 END TREATMENT (1995) Proper end treatment is critical to protect the culvert pipe from washout, piping, undermining, scour, etc. Slope paving, rip rap, headwalls/wingwalls, end sections, cutoff walls and toe walls are possible end treatment details which can be incorporated into culvert design. Warped fill embankments may be needed to provide balanced loading near the ends of culverts that are skewed to the embankment. See Figure 1-4-24 for clarification. Protection of the pipe culvert installation from hydraulic action is critical during all phases of construction. 4.12.10 PROTECTION OF PIPE CULVERT FROM CONSTRUCTION LOADS (1995) It is important to protect pipe culvert structures throughout the construction process because the structure does not develop full structural capacity until it is properly installed in an adequate backfill envelope including sufficient minimum cover for anticipated live loads. Heavy construction equipment must not cross the pipe culvert until sufficient minimum cover height has been achieved. In addition, heavy equipment is to be kept away from the sides of the pipe culvert to avoid unbalanced loading and possible culvert distortion or displacement. The culvert manufacturer should be contacted regarding any questions about minimum cover and equipment loads. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-74 AREMA Manual for Railway Engineering Culverts 1 3 Figure 1-4-24. Using Warped Fill to Balance Loads Across Ends of Culverts 4.12.11 SAFETY PROVISIONS (1995) Individual railroads may require specific precautions as deemed advisable to insure the safety of the trains, tracks and construction workers throughout the pipe culvert installation process. Regardless of the installation methods chosen, the track must be adequately supported during construction. All procedures involved in the installation must comply with applicable guidelines and regulations, including OSHA requirements. SECTION 4.13 EARTH BORING AND JACKING CULVERT PIPE THROUGH FILLS 4.13.1 GENERAL (1995) a. Where conditions are suitable, the installation of pipe culverts by jacking and/or earth boring can be a viable alternative to more standard methods of installation such as open cut or tunneling. Possible advantages of jacking or boring include: (1) Lower cost. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-75 4 Roadway and Ballast (2) Minimal interruption of traffic. (3) Minimal disturbance of roadbed. b. Costs may be higher, although not necessarily prohibitive, in unstable soils and embankments containing boulders, stumps, waste from rock cuts, or similar obstructions. c. Before it is decided that jacking is the proper method to use, all conditions involved in the operation should be investigated. Cost estimates for open cut placement or tunneling should be compared with the probable cost for jacking and/or boring. Such estimates should include expenses due to interference with traffic and excess maintenance until embankment becomes stabilized. Additionally, relative safety of the various installation methods must be considered. The exposed vertical face associated with the jacking operation may not be desirable in certain soil conditions and should be addressed by a qualified engineer. d. It is recommended that pipe boring and jacking operations be performed by an experienced specialty contractor normally engaged in performing this type of service. Most railroad maintenance-of-way departments are not equipped to undertake such a project. e. For further information on earth boring and jacking methods refer to Reference 27. 4.13.2 TYPE OF PIPE SUITABLE FOR JACKING (1992) a. Ideally pipe materials to be used in the boring and jacking process should have a smooth exterior wall. The most commonly used materials for pipes installed by the boring and jacking contractor are smooth wall steel pipe or tongue and groove circular concrete pipe. Other shapes, such as precast reinforced concrete box sections and reinforced concrete elliptical pipe sections, have been successfully jacked. Under certain conditions, corrugated metal pipe can also be jacked. b. Concrete pipe is manufactured with tongue and groove joints which provide a smooth outside surface. An appropriate class of concrete pipe should be selected to provide the compression strength to resist the axial forces imposed by jacking. Supplemental joint reinforcing may be required if eccentric loading of the joint is a possibility. 4.13.3 SIZE AND LENGTH OF PIPE (1992) a. The size of pipe that can be placed by jacking will vary with local site conditions. The jacking contractor and pipe manufacturer should be consulted regarding suitable size and length limits. b. Concrete pipe sections are usually manufactured in eight foot lengths; however, other lengths may be available. 4.13.4 PRECAUTIONS IN UNSTABLE SOILS (1992) a. The jacking method is not well adapted to placing pipe in unstable soils, unless certain precautions are taken. Before undertaking an operation of this kind a thorough investigation of conditions should be made. Borings into the fill where there is doubt as to the nature of the material may be desirable. Unstable soil conditions should be evaluated by a qualified geotechnical engineer for recommendations on the most appropriate method of soil stabilization. b. If jacking is decided upon it will probably be beneficial to work continuously to minimize the tendency of the material to “freeze” around the pipe. However, lubricants such as bentonite slurry are available to minimize the freezing tendency. The approach trench should be properly sheeted and braced on the sides and working face. Wet sandy soils can be de-watered by various means including well points. The excavation should not be carried more than a few inches ahead of the pipe. If the pipe seizes, jacking may have to be done from both ends, or installation of intermediate hydraulic jacking stations may be required. In some instances, switching to trenching or open cut methods may be required. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-76 AREMA Manual for Railway Engineering Culverts c. Excessive voids shall not be permitted in the jacking process. Grout points shall be installed in pipe and all voids shall be filled by pressure grout as soon as possible after the completion of the project. 4.13.5 PROTECTION OF PIPE AGAINST PERCOLATION, PIPING AND SCOUR (1992) a. If it is anticipated that the pipe will discharge under head for any considerable period, and particularly if it lies in easily eroded material, precautions against percolation or piping along the outside should be taken. b. Concrete collars, grout injected collars, cut-off walls, slope paving or similar impermeable slope barriers should be considered as a precaution against percolation or piping along the outside of the conduit. c. Should it be necessary to protect the ends against scour, concrete pavement or riprap can be provided at the end of the pipe. In extreme cases energy dissipaters can be used to reduce the outlet velocity of flow to acceptable limits. 4.13.6 SAFETY (1992) Trenching is one of the most dangerous situations in modern construction. Since a jacking operation generally involves some form of trenching or pit construction, the jacking contractor or railway forces must strictly conform to all Federal, State and local regulations and in particular, the requirements of the Occupational Safety and Health Administration (OSHA). 1 SECTION 4.14 CULVERT REHABILITATION 4.14.1 GENERAL (1992) a. The purpose of this part of the Manual is to guide the design engineer in his decision to rehabilitate or replace deteriorated or failing culverts and to recommend methods for the culvert rehabilitation or repair. b. While the magnitude of rehabilitation may at times appear enormous, rehabilitation often is very cost effective when compared to the alternative of new construction. c. It is recommended that a regular program of culvert inspection and evaluation be instituted to identify deteriorated and/or failing culvert sections. 4.14.2 SURVEY OF EXISTING STRUCTURES (1992) a. Once a problem is identified, a careful survey should be made of the existing structure to determine the exact size and shape. It is necessary to know the exact cross-section of the opening at all limiting points, the alignment of the structure with respect to its centerline, and whether projecting parts of the existing culvert can be removed. Any old falsework piling, boulders or ledge rock in the waterway that might interfere with rehabilitation efforts should be noted. In addition, the structural integrity of the culvert and the foundation conditions under the existing structure should be evaluated. b. Given the above information, the design engineer can effectively consider the comparative advantages of rehabilitation or replacement of the culvert. Items of consideration should include: (1) Extent of critical nature of the deterioration. (2) Available track time. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-77 3 4 Roadway and Ballast (3) Site accessibility. (4) Available time that flow can be restricted. (5) Useful service life/life-cycle cost analysis. (6) Required hydraulic capacity. (7) Environmental considerations. 4.14.3 METHODS OF REHABILITATION (1992) If the decision is to rehabilitate the culvert, the design engineer has several options to consider. Methods of culvert rehabilitation include: a. Localized repairs. b. Reline the existing structure. (1) Slip line with slightly smaller diameter pipe or tunnel liner plate. (2) Inversion lining. (3) Shotcrete lining. (4) Cement mortar lining. c. In place installation of concrete invert. Other methods of pipeline rehabilitation are available, but some may not be practical for culverts. 4.14.4 LOCALIZED REPAIRS (1992) In some cases it is practical to consider localized repair. This can be an economical solution when the overall condition of the culvert is still performing as designed but has isolated areas of deterioration that if left unattended would lead to major problems in the future. Techniques that are available to the engineer include: a. Grouting. Voids in the backfill caused by leaking joints or pipe wall perforations can be filled by pumping a sand-cement mortar grout into the void. This can be done from the inside if the structure is large enough or from the outside of shallow buried structures. Filling the void with grout should prevent further loss of backfill. b. Patching. Localized damage to linings, coatings or pavements in culverts can be patched to prolong the life of a drainage structure. The area to be repaired should be properly cleaned and the repair material should match the original material if possible. c. Internal Expanding Bands. Pipe joints that have become separated to a degree where loss of backfill is a threat to the grade of the track above the structure can be repaired with bands couplers that are tightened from inside the pipe. These bands then expand against the inside wall to form a seal. d. Sealing. Elastomeric grout can be used effectively to seal and prevent loss of fine backfill through open pipe joints. This grout is mechanically pushed into the open joint with the aid of an inflatable bladder. The chemical grout turns into an elastomeric seal immediately upon contact with water. This material is normally not used to fill voids because of its cost. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-78 AREMA Manual for Railway Engineering Culverts 4.14.5 RELINING MATERIALS (1992) The selection of the reline material is dependent upon the condition of the conduit to be rehabilitated and its diameter and/or shape. If the line has deteriorated to the point that it is structurally deficient, the rehabilitation should have sufficient structural capability to withstand the imposed dead and live loads. 4.14.5.1 Sliplining a. If after hydraulic evaluation, the downsizing of the existing line is acceptable, then standard corrugated metal pipe may be used and provided in lengths which would facilitate insertion. Hydraulic advantages may be gained by improvements to inlet details (see Article 4.8.3.1) or by using helical corrugated steel pipe if the existing pipe is annularly corrugated. b. Hydraulic capacity can be maximized by the use of lined metal pipe. Choices of this type of pipe include: (1) 100% asphalt lined. (2) 100% cement mortar lined. (3) Double-wall CMP. (4) Spiral rib CMP. c. Connection of the liner pipe segments can be achieved with either internal or external adjustable bands depending upon the available clearance within the culvert. d. If the culvert to be relined is large enough for a person to enter, “guide rails” may be installed to insure that the proper alignment and grade of the liner pipe is maintained. If the lining of the pipe is to be placed at the same grade as the pipe being lined, skid bars attached to the lining pipe are used in lieu of the guide rails. Also it is common practice to specify grout plugs and hold-down devices (Figure 1-4-25). e. Where physical constraints and/or safety concerns limit the use of the liner pipe sections, it may become necessary to use tunnel liner plates. This permits the entire assembly to be erected from inside the structure. f. After the liner pipe has been secured in place, the annular space between the liner pipe and the existing culvert should be filled. Suitable fill material will vary depending on the type and size of structure, the area to be filled, the equipment available and the structural requirements. Typical materials (referred to as CLSM, Controlled Low Strength Material) include cement or chemical grout, concrete slurry and sand. g. Care must be taken during filling to eliminate voids. Filling must be done in a balanced fashion and in a manner that does not cause deformation of the lining pipe. The lining pipe may need to be internally braced © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-79 1 3 4 Roadway and Ballast (or externally blocked) to resist grouting pressure. The lining pipe may also need to be secured to resist flotation during grouting. Figure 1-4-25. CMP Liner Pipe Installation Showing Guide Rails, Grout Plugs and Adjusting Rods 4.14.5.2 Inversion Lining a. Inversion lining is accomplished by using needle felt, of polyester fiber, which serves as the “form” for the liner. The use of this method requires that the pipe be taken out of service during the rehabilitation period. One side of the felt is coated with a polyurethane membrane and the other is impregnated with a thermostating resin. b. The physical properties of the felt and chemicals must be determined for the specific project. c. Inversion lining is most commonly accomplished by specialized contractors in rehabilitation of sanitary sewers and storm sewers and is not often practical in culvert rehabilitation. 4.14.5.3 Shotcrete Lining a. Shotcrete is a term used to designate pneumatically applied cement plaster or concrete. A gun operated by compressed air is used to apply the cement mixture. b. When properly made and applied, shotcrete is extremely strong, dense concrete and resistant to weathering and chemical attack. For relining existing structures, the shotcrete typically is from 2 to 4 inches thick depending on conditions and may be steel reinforced. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-80 AREMA Manual for Railway Engineering Culverts 4.14.5.4 Cement Mortar Lining a. For small diameter pipe which is not easily accessible, a cement mortar lining may be applied. b. This method involves the use of a mortar projection machine and an attached mechanical trowel. The assembly is pulled through the culvert as mortar is applied to the interior surface and troweled. 4.14.6 IN PLACE INSTALLATION OF CONCRETE INVERT (1992) a. In some cases, the deterioration of the culvert may be limited to the invert. The upper segment may still exhibit acceptable structural integrity and rehabilitation with a cast-in-place reinforced concrete invert may be an acceptable alternative (Figure 1-4-26). b. This method is generally limited to larger diameter pipes where it is possible for a person to enter and work within the conduit. c. Prior to placing the new invert, it is necessary to divert the stream flow, remove debris and loose material, and clean the area to receive the new concrete. Next, a reinforcing mesh or bars are secured to the original culvert. Then an appropriate thickness of concrete is applied to the invert and troweled smooth to conform to the shape of the bottom of the culvert. d. An epoxy type sealer may be applied to the concrete invert to seal the concrete pores and increase service life. e. The engineer or designer may also want to refer to Chapter 8, Concrete Structures and Foundations, Part 14, Repair and Rehabilitation of Concrete Structures. 1 3 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-81 Roadway and Ballast Figure 1-4-26. Example of New Invert in CMP SECTION 4.15 SPECIFICATION FOR STEEL TUNNEL LINER PLATES 4.15.1 GENERAL (1992) 4.15.1.1 Scope These specifications cover cold-formed steel tunnel liner plates, fabricated to permit in-place assembly of a continuous steel support system as excavation of the tunnel progresses. 4.15.1.2 Authority of Engineer The engineer shall decide which type of tunnel liner plate shall be used and his decision shall be final. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-82 AREMA Manual for Railway Engineering Culverts 4.15.2 MATERIAL (1992) 4.15.2.1 Plates a. The tunnel liner plates shall be fabricated from structural quality, hot-rolled, carbon-steel sheets or plates conforming to ASTM Specification A 569. b. The mechanical properties of the flat plate before cold forming shall be: Tensile strength, psi . . . . . . . . . 42,000 min Yield strength, psi . . . . . . . . . . . 28,000 min Elongation in 2, % . . . . . . . . . . 30 min 4.15.2.2 Bolts a. Bolts and nuts used with lapped seams shall be not less than 5/8 inches in diameter. The bolts shall conform to ASTM Specification A 449 for plate thicknesses equal to or greater than 0.209 inches and A 307 for plate thicknesses less than 0.209 inches. The nut shall conform to ASTM Specification A 307, Grade A. b. Bolts and nuts used with four flanged plates shall be not less than1/2 inch in diameter for plate thicknesses to and including 0.179 inch and not less than 5/8 inch in diameter for plates of greater thickness. The bolts and nuts shall be quick-acting coarse thread and shall conform to ASTM Specification A 307, Grade A. 1 4.15.3 FABRICATION (1992) 4.15.3.1 Plate Size and Weight The plate width shall be l6 or 18 inch. The plate lengths shall provide circumferential wall coverage in two or more multiples equivalent to 6, 12, 14 or 16 inch of diameter. The maximum weight of a single plate without bolts shall be 90 lb. 3 4.15.3.2 Plate Joints All plates shall be punched for bolting on both longitudinal and circumferential seams or joints and shall be so fabricated as to permit complete erection from the inside. 4 4.15.3.2.1 Circumferential Bolt spacing in circumferential flanges shall be not more than 92 inches center to center and shall be a multiple of the plate length so that plates having the same curvature are interchangeable and will permit staggering of the longitudinal seams. 4.15.3.2.2 Longitudinal 4.15.3.2.2.1 Four-Flanged Plates The longitudinal flanges shall be punched to accommodate 3 bolts in a 16 inch plate width. 4.15.3.2.2.2 Two-Flanged Plates The longitudinal lapped seams shall be punched to accommodate 4 bolts per foot. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-83 Roadway and Ballast 4.15.3.3 Plate Configuration All plates shall be cold formed to provide a pattern of corrugations or panels in the skin section, which, along with the circumferential flanges, will develop the effective sectional properties shown in Table 1-4-38. 4.15.4 COATINGS (1992) Steel liner plates are often used only to maintain the tunnelled opening until a carrier pipe is installed and backpacked. In such use the liner is expendable and no purpose is served by extending its life. If the steel liner plates compose the finished structure, then the expense of corrosion-resistant coatings is justified. 4.15.4.1 Zinc Coating When required, and so specified, the liner plates shall be galvanized to meet the requirements of AREMA Specification for Corrugated Structural Plate Pipe, Pipe Arches and Arches. Bolts and Nuts shall be galvanized to meet the requirements of ASTM Specification A 153. 4.15.4.2 Bituminous Coating In addition, when so specified, the liner plates shall be bituminous-coated to meet the requirements of AREMA Specification for Bituminous Coated Corrugated Metal Pipe and Arches. 4.15.5 DESIGN (1992) 4.15.5.1 General a. These criteria cover the design of cold-formed panel steel tunnel liner plates. The minimum thickness shall be as determined by design in accordance with Article 4.15.5.2, Article 4.15.5.3, Article 4.15.5.4, Article 4.15.5.5, and Article 4.15.5.6. The construction shall conform to Section 4.16, Construction of Tunnel Using Steel Tunnel Liner Plates and Table 1-4-38. b. The supporting capacity of a nonrigid tunnel lining such as a steel liner plate results from its ability to deflect under load so that side restraint developed by the lateral resistance of the soil constrains further deflection. Deflection thus tends to equalize radial pressures and to load the tunnel liner as a compression ring. c. The load to be carried by the tunnel liner is a function of the type of soil. In a granular soil, with little or no cohesion, the load is a function of the angle of internal friction of the soil and the diameter of the tunnel being constructed. In cohesive soils such as clays and silty clays the load to be carried by the tunnel liner is affected by the shearing strength of the soil above the roof of the tunnel. d. A subsurface exploration program and appropriate soil tests should be performed at each installation before undertaking a design. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-84 AREMA Manual for Railway Engineering Culverts Table 1-4-38. Effective Sectional Properties Based on the Average of One Ring of Plates Thickness (Inches) Area (Inch 2/Inch) Moment of Inertia (Inch 4/Inch) Radius of Gyration (Inch) 18 inch Wide – 2 Flange Plates 0.075 0.105 0.135 0.164 0.179 0.209 0.239 0.096 0.135 0.174 0.213 0.233 0.272 0.312 0.034 0.049 0.064 0.079 0.087 0.103 0.118 0.60 0.60 0.61 0.61 0.61 0.62 0.62 16 inch Wide – 4 Flange Plates 0.105 0.120 0.135 0.164 0.179 0.209 0.239 0.313 0.375 0.0656 0.0759 0.0851 0.1040 0.1140 0.1380 0.1510 0.1930 0.2290 0.0398 0.0468 0.0517 0.0709 0.0771 0.0904 0.1180 0.1620 0.2200 0.41 0.41 0.41 0.44 0.44 0.44 0.47 0.49 0.52 1 4.15.5.2 Loads The external load on a circular tunnel liner made up of tunnel liner plates, may be predicted by various methods. In cases where more precise methods of analysis are not employed, the external load P can be predicted by the following: a. If the grouting pressure is greater than the computed external load, the external load P on the tunnel liner shall be the grouting pressure. b. In general the external load can be computed by the formula: EQ 4-15 P = P1 + Pd where: P = the external pressure on the tunnel liner P1 = the vertical pressure at the level of the top of the tunnel liner due to live loads Pd = the vertical pressure at the level of the top of the tunnel liner due to dead load Values of P1 for Cooper E 80 live load, including an allowance of 50% for impact, are approximately as shown in Table 1-4-39. c. Values of Pd may be calculated using modified Marston’s formula for load as follows, or any other suitable method. EQ 4-16 Pd = Cd W D © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-85 3 4 Roadway and Ballast Table 1-4-39. Live Loads, Including Impact, for Various Heights of Cover for Cooper E 80 (See Note 1) Height of Cover (Ft) Load Lb/Ft2 2 3800 5 2400 8 1600 10 1100 12 800 15 600 20 300 30 100 Note 1: If height of cover (from bottom of cross tie to top of structure) is over 30 feet, use dead load only. For live load other than Cooper E 80, the above values should be accordingly adjusted. d. In the absence of adequate borings and soil tests, the full overfill height should be the basis for Pd in the tunnel liner plate design. Values of Pd may be calculated using Marston’s formula where: Cd = coefficient for tunnel liner (Figure 1-4-27) W = total (moist) unit weight of soil D = horizontal diameter or span 4.15.5.3 Structural Criteria The following criteria must be considered in the design of liner plates: a. Joint strength. b. Handling and installation strength. c. Critical buckling of linear plate wall. d. Deflection or flattening of tunnel section. 4.15.5.4 Joint Strength a. Seam strength for liner plates must be sufficient to withstand the thrust developed from the total load supported by the liner plate. This thrust, T, in pounds per lineal foot is: PD T = --------2 EQ 4-17 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-86 AREMA Manual for Railway Engineering Culverts Ø = soil friction angle H = height of cover 1 Figure 1-4-27. Diagram for Coefficient Cd for Tunnels in Soil where: 3 P = load as defined in Article 4.15.5.2 D = diameter or span in feet b. Ultimate design longitudinal seam strengths are found in Table 1-4-40. c. Thrust, T, multiplied by the safety factor, should not exceed the ultimate seam strength. 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-87 Roadway and Ballast Table 1-4-40. Longitudinal Seam Strengths Plate Thickness Inches Ultimate Strength, Kips/Ft 2 flange 4 flange 0.075 20.0 – 0.105 30.0 26.4 0.135 47.0 43.5 0.164 55.0 50.2 0.179 62.0 54.5 0.209 87.0 67.1 0.239 92.0 81.5 0.250 – 84.1 0.313 – 115.1 0.375 – 119.1 4.15.5.5 Minimum Stiffness for Installation The liner plate ring shall have enough rigidity to resist the unbalanced loadings of normal construction: grouting pressure, local slough-ins and miscellaneous concentrated loads. The minimum stiffness required for these loads can be expressed for convenience by the formula below. It must be recognized, however, that the limiting values given here are only recommended minimums. Actual job conditions may require higher values of effective stiffness. Final determination on this factor should be based on intimate knowledge of a project and practical experience. EI Minimum Stiffness = ------D2 EQ 4-18 where: D = diameter in inches E = modulus of elasticity, psi I = moment of inertia, in.4/in. EI For 2-Flange ------- = 50 minimum D2 EI For 4-Flange ------- = 110 minimum D2 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-88 AREMA Manual for Railway Engineering Culverts 4.15.5.6 Critical Buckling of Liner Plate Wall a. Wall buckling stresses are determined from the following formulas: f 2 r 24E u KD 2 For diameters less than ---- ----------- : f c = f u – ---------- -------- in psi K fu 48E r r 24E 12E in psi For diameters greater than -------------- : f c = ----------------2 K fu KD -------r EQ 4-19 EQ 4-20 where: fu = minimum specified tensile strength, psi fc = buckling stress, psi, not to exceed specified yield strength K = soil stiffness factor, which will vary from 0.22 for soils where Ø > 15 to 0.44 where Ø < 15 to 0.44 D = pipe diameter, inches r = radius of gyration of section E = modulus of elasticity, psi b. 1 Design for buckling is accomplished by limiting the ring compression thrust T to the buckling stress multiplied by the effective cross section area of the liner plate divided by the factor of safety: f cA T = --------FS EQ 4-21 3 where: T = thrust per lineal foot from Article 4.15.5.4 A = effective cross section area of liner plate, square inches per foot FS = factor of safety for buckling 4 4.15.5.7 Deflection or Flattening a. Deflection of a tunnel depends significantly on the amount of over excavation of the bore and is affected by delay in backpacking or inadequate backpacking. The magnitude of deflection is not primarily a function of soil modulus or the liner plate properties, so it cannot be computed with usual deflection formulas. b. Where the tunnel clearances are important, the designer should oversize the structure to provide for a normal deflection. Good construction methods should result in deflections of not more than 3% of the nominal diameter. 4.15.5.8 Safety Factors Longitudinal seam strength . . . . 3 Pipe wall buckling. . . . . . . . . . . . 2 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-89 Roadway and Ballast SECTION 4.16 CONSTRUCTION OF TUNNEL USING STEEL TUNNEL LINER PLATES 4.16.1 SCOPE (1992) These specifications are intended to cover the installation of tunnel liner plates in tunnels constructed by conventional tunnel methods. For the purposes of these specifications, tunnels excavated by full face, heading and bench, or multiple drift procedures are considered conventional methods. Liner plates used with any construction procedure utilizing a full or partial shield, a tunneling machine or other piece of equipment which will exert a force upon the liner plates for the purpose of propelling, steering or stabilizing the equipment are considered special cases and are not covered by these specifications. 4.16.2 DESCRIPTION (1992) a. This item shall consist of furnishing cold formed steel tunnel liner plates conforming to these specifications and of the sizes and dimensions required on the plans, and installing such plates at the locations designated on the plans or by the engineer, and in conformity with the lines and grades established by the engineer. The completed liner shall consist of a series of steel liner plates assembled with staggered longitudinal joints. Liner plates shall be fabricated to fit the cross section of the tunnel. Liner plates herein described must meet the section properties — thickness, area, and moment of inertia — as listed in Table 1-4-38. b. All plates shall be connected by bolts on both longitudinal and circumferential seams or joints and shall be so fabricated as to permit complete erection from the inside. c. Grout holes 2 inches or larger in diameter shall be provided as shown on the plans to permit grouting as the erection of tunnel liner plates progresses. 4.16.3 INSTALLATION (1992) a. All liner plates for the full length of a specified tunnel shall be of one type only, either the flanged or the lapped seam type of construction. b. Liner plates shall be assembled in accordance with the manufacturer’s instructions. c. Coated plates shall be handled in such a manner as to prevent bruising, scaling, or breaking of the coating. Any plates that are damaged during handling or placing shall be replaced by the contractor at his expense, except that small areas with minor damage may be repaired by the contractor as directed by the engineer. d. Voids occurring between the liner plate and the tunnel wall shall be force-grouted. The grout shall be forced through the grouting holes in the plates with such pressure that all voids will be completely filled. The frequency of grouting shall be as directed by the engineer. e. Full compensation for backpacking or grouting shall be considered as included in the contract price paid for tunnel and no separate payment will be made therefor. 4.16.4 MEASUREMENT (1992) The length of tunnel to be paid for will be the length measured on the tunnel liner plate invert. 4.16.5 PAYMENT (1992) Payment for the footage of each size of tunnel as determined under measurement shall be paid for at the contract unit prices per lineal foot bid for the various sizes, which payment shall include full compensation for furnishing all labor, materials, tools, equipment and incidentals to complete this item, including removal and disposal of material resulting from the excavation of the bore and force-grouting voids. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-90 AREMA Manual for Railway Engineering Culverts SECTION 4.17 CULVERT INSPECTION 4.17.1 INTRODUCTION (2001) a. Railroad rights-of-way across North America contain numerous culvert structures, in a variety of sizes and made from a variety of materials, buried beneath the track structure. Culverts, just like any other type of structure, require maintenance and inspection on a regular basis in order to perform as intended. However, items critical to a culvert inspection may not be those typically associated with a bridge inspection and special training is required. b. Lack of knowledge regarding proper installation, inspection and maintenance is a primary cause of poor performance of culverts and other drainage structures. The fact that culverts are buried in an embankment and are not generally visible at track level contributes to the problem since they usually do not receive the same attention that bridges, tunnels and other major structures receive. A failure of a culvert structure can have the same catastrophic result as a bridge or tunnel collapse. Routine and proper inspection of railway culverts is not only recommended but is necessary to assure that these important structures are functioning as originally designed. 4.17.2 DEFINITION OF A CULVERT (2001) a. A culvert can be defined as a drainage opening or conduit passing through an embankment for the purpose of conveying water. Culverts are usually hydraulic conduits; however, short span structures such as a cattlepass or pedestrian underpass would fall under the general classification of culverts. b. Culverts, unlike bridges, have no definite distinction between substructure and superstructure. While some agencies distinguish between bridges and culverts based solely on size, with spans of 10' frequently selected as the limiting factor, the true difference is the basis upon which culverts are designed - both structurally and hydraulically. 1 4.17.3 KEY DIFFERENCES FROM BRIDGES AND OTHER STRUCTURES (2001) 3 4.17.3.1 Structural Differences Between Culverts and Bridges a. Culverts are designed to support not only the live load of railway traffic but also the dead load of the soil and track structure above. However, the live load becomes less of a factor as the depth of cover above the culvert increases, due to distribution of the live load through the soil. Bridges do not generally have an overburden of soil above the spanning elements. b. Flexible culverts essentially function as a soil-structure interaction system. The quality and stability of soil materials surrounding most culvert structures are critical to their ability to carry load. While rigid culverts (such as reinforced concrete, thick walled metal pipe, etc.) are designed differently than flexible culverts, there still is a degree of dependency upon quality of backfill surrounding the culvert. The type of backfill and degree of compaction affect side support and foundation support. Bridges, on the other hand, are usually designed to transfer vertical loads to the subsurface by way of piles or spread footings. 4.17.3.2 Hydraulic Differences Between Culverts and Bridges a. Most culverts are designed to operate efficiently under submerged inlet conditions. As flow increases, ponding occurs at the upstream end of the culvert. The resultant rise in water surface elevation increases the head at the inlet end and increases hydraulic capacity of the culvert, provided, of course, that proper end treatment, cutoff walls, embankment slope protection, etc. are incorporated into the design. b. Bridges are not usually designed to create a restriction of flow at the upstream end of the structure. In fact, most bridges are designed to pass the maximum amount of flow without submerging any of the spanning elements. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-91 4 Roadway and Ballast c. Scour protection of footings - whether for bridge abutments or piers or for arch-type culverts - is a concern common to bridges and culverts. 4.17.3.3 Inspector Qualifications and Training a. While actual inspection items, techniques, etc. are discussed later in this section, it is important to distinguish between culverts and bridges when it comes to several visual observations. Many bridge inspectors are trained to look for cracks, rust, spalling concrete, exposed rebar, etc. as signs of obvious distress. While such factors may be a valid concern for culverts, oftentimes minor problems such as surface rusting and perforations are noted while culvert deflection, distortion, embankment settlement, erosion, and other more serious factors are ignored. b. Inspectors must be trained to recognize the critical factors involved with inspection of culverts. The culvert inspector should have knowledge of how culverts function, hydraulically and structurally, and the significance of defects that may be found during inspection, along with the load bearing capacity that the culvert must maintain. The culvert inspector must be capable of working under physically demanding conditions, including cramped spaces, rugged terrain, steep embankments, and in and around water. The inspector must also be able to read plans, construction documents, inspection reports, and have a knowledge of the use of various types of measuring devices, and also the ability to use a surveyors level when necessary. c. The inspector should have a minimum of 2 years of culvert inspection assignments, working under the supervision of a qualified culvert inspector, and/or should have completed a comprehensive training course for culvert inspection on the subjects as outlined in Paragraph b above. 4.17.4 SAFETY (2001) a. Culvert inspection in many cases presents certain hazards to personnel performing the inspection. In order to properly evaluate the structural integrity of a culvert, it is usually necessary to perform an internal inspection of the conduit. Many smaller diameter culverts may exist under railroad properties which makes internal inspection difficult. It is recommended that culverts less than 30 inches in diameter not be entered by inspection personnel without special precautions. Internal inspection of culverts in this size range is best conducted using specially designed video cameras, deflection recording devices, or similar methods. Culverts 30 inches in diameter and larger should only be entered by inspection personnel trained in working within confined spaces and using procedures in full compliance with all applicable State, Local and Federal regulations (i.e., OSHA, Roadway Workers Protection Act, and other FRA regulations). b. Most railroad culverts are located at the base of relatively steep embankments and many contain high parapet and/or wingwalls. At such locations, fall protection measures should be implemented. Fast moving water may also present additional hazards. Culverts should never be entered if water depths in combination with flow velocity make conditions potentially dangerous. Even low flow depths can cause problems with footing, etc. and care must be taken. As with any maintenance-of-way function, the risk of working along an active railroad is also a consideration. c. Inspectors and maintenance workers should never enter culverts if conditions or the structural integrity of the culvert appear questionable. However, the appropriate railway office should be notified of the culvert problems as soon as possible. d. In light of the risks associated with culvert inspection, it is necessary that culvert inspectors receive adequate training prior to undertaking any field inspection of culvert facilities. If a railroad or transit company does not have adequately trained culvert inspection personnel, it is recommended that internal inspection services be contracted to a specialty firm. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-92 AREMA Manual for Railway Engineering Culverts 4.17.5 INVENTORY, ASSESSMENT OF EXISTING CONDITIONS, AND FREQUENCY OF INSPECTION (2001) 4.17.5.1 Inventory It is important and extremely useful to develop a comprehensive list of all existing culvert structures, in a logical order, so that a specific culvert can easily be found when necessary. This is generally done in several ways. One would be to provide a system map, or a series of division or regional maps of the railroad system, showing location of each culvert and structure by milepost and also with a brief description of the culvert at each location. This provides a quick easy reference for determining the location of culverts for upcoming inspections, and also for the location of culverts that might fall within other types of construction projects. In addition to this, a comprehensive listing by line segment, and milepost order, along with a listing of the structural characteristics, age, skew angle, and general condition, is probably the most useful for documenting all culvert structures. 4.17.5.2 Assessment of Existing Conditions It is important that any inventory of existing culvert structures contain not only the specific structural characteristics of the culvert, but also an assessment of existing conditions which relate directly to the condition and future life of that culvert. This listing is very useful in planning future culvert maintenance and replacement, and is also a very valuable tool in planning periodic, intermediate culvert inspections. This listing should be updated annually with current inspection results, and it is also important, of course, to update this listing with the addition of new culverts and by the deletion of culverts that have been retired and removed, so that the information provided is accurate and current. Any modifications to the adjacent drainage area that may affect the hydraulic performance of the culvert should be noted. 4.17.5.3 Frequency of Inspection a. Following an initial assessment, the frequency of inspection is dependent upon the age and condition of the culverts within the system. It is suggested that every culvert in the system be inspected at least every five years. A specific culvert condition or deficiency along with specific types of soil conditions, and other local conditions, may require more frequent inspections, and this should be determined by a qualified inspector. b. It is advisable that interim inspections be carried out immediately after major rain storms, or any time when it is known that the culvert, or culverts in question, have been subjected to heavy run off or very high stream flows. These inspections should be made as soon after a major storm as possible, or at least before the track is to be used again. It may also be advisable to have a listing of specific culverts and locations which are susceptible to high runoff, heavy drift loads, ice flow or severe scour. c. Areas that have significant construction and new development occurring in the upstream watershed should receive interim inspections. 4.17.6 PHYSICAL CONDITION ASSESSMENT (2001) 4.17.6.1 Condition of Roadbed/Track Surface a. Quite often a track irregularity, such as an alignment problem or a settlement problem, is indicative of the fact that the underlying culvert is possibly failing in some manner. It is important, not only for the culvert inspector to be aware of this, but also for the personnel doing periodic track inspections to be aware of locations of culverts. Any track irregularities over a culvert should be communicated to the appropriate railway office for a follow-up culvert inspection. Track conditions that may indicate underlying culvert problems include track alignment irregularities, track settlement, side-slope failures, and also scouring of side slopes by recent water flow. b. In some cases, culvert problems may be due to settlement or movement of the fill around the culvert. Part 1 Roadbed, discusses precautions that should be taken to avoid this problem. Culvert distress may also occur © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-93 1 3 4 Roadway and Ballast without attendant roadbed surface or track alignment problems. Lack of surface problems does not supersede the need for thorough periodic culvert inspections. 4.17.6.2 Condition of Upstream/Downstream Channel a. In addition to structural failure, a culvert can also fail hydraulically. Culverts that are plugged, damaged, improperly installed, or not sized properly usually are not capable of handling the flows needed to maintain good drainage under the track and roadbed structure. b. The culvert should be inspected to see that it is well aligned with the stream channel both vertically with the streambed profile and horizontally with the channel alignment. Loss of embankment, inlet and outlet scour, and backwater conditions may be symptoms of inadequate culvert capacity. c. In some cases, the installation of pavement, riprap, headwalls, toe walls, and/or collars may improve a culvert’s hydraulic performance. If such structures are already in place, they should be inspected closely for damage, proper location and sizing, and hydraulic performance. Drift problems, turbulence, or other impediments to smooth stream flow through the culvert should be noted. See 4.1.1 Waterway Required (1995), for more information. 4.17.6.3 Visual Appearance a. The culvert inspector must be aware of the important aspects related to visual appearance of the culvert as they pertain to the type of culvert (i.e., rigid or flexible) and the culvert material (i.e., metal, concrete, plastic, etc.). Problems vary in relevancy and significance depending upon culvert type and culvert material. A proper inspection of a culvert must start with the determination of culvert type and identification of culvert material. b. Observation should be made of the actual shape of the culvert as compared to original design geometry. If irregularities in cross-sectional shape are observed, the culvert must be inspected carefully to determine if it is structurally sound. It may be necessary to perform interim inspections to observe whether the culvert is continuing to deform. c. Deviations in alignment as compared to previous inspection records or as-built conditions should be assessed for risk to culvert performance. Changes in vertical or horizontal alignment may indicate unstable or poorly compacted support soils, or may also indicate the displacement of soils caused by water flowing along and/or under the pipe through the subgrade, also referred to as “piping”. 4.17.6.4 Physical Condition of Culvert There are a number of physical manifestations of possible distress in culverts. This section discusses some of these problems in general terms; however, the significance of such problems will vary depending upon the culvert type and material. Refer to Report No. FHWA-IP-86-2 Culvert Inspection Manual - Supplement to the Bridge Inspector’s Training Manual (Reference 11) and An Empirical Approach for Predicting Deflection in Large Metal Culverts (Reference 19) for more detail regarding further investigation of specific defects. 4.17.6.4.1 Corrosion Corrosion may be due to soils or effluent with an extreme pH or restivity and/or the presence of contaminants. Evidence of corrosion will vary depending upon the type of culvert material. Corrosion is typically manifested by rusting, perforations or metal loss in a metal culvert and by spalling of concrete and exposed reinforcing steel in a concrete culvert. The amount of corrosion that has developed in the culvert, particularly along the culvert flow line, should be noted. It must be determined as to whether a loss of section is impairing the culvert’s ability to carry the prescribed loads. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-94 AREMA Manual for Railway Engineering Culverts 4.17.6.4.2 Abrasion Abrasion may be a critical component of deterioration for all types of culverts. Abrasion may wear away any protective coatings and allow corrosion to begin and proceed at an accelerated rate. Abrasion is critical as it will reduce the cross sectional area of the wall and eventually impair the integrity and load bearing capacity of the culvert. Abrasion will occur particularly in pipes with steep gradients, and also in areas where high flow rates carrying sand and rocks can wear away the culvert invert. 4.17.6.4.3 Coating Loss Coatings are intended to extend the life or improve hydraulic performance of the culvert. Coating loss can occur by a chemical reaction or by abrasion and may be followed by increased corrosion of the culvert; loss of structural integrity; and/or reduction in hydraulic capacity. 4.17.6.4.4 Perforations Perforations of the culvert wall are also evidence of abrasion and/or corrosion and are indicative of loss of wall thickness. This could represent a severe condition. The culvert should be evaluated to ascertain the extent of metal loss and to determine if it is losing its structural integrity (and load bearing capacity). Severely perforated culvert wall sections may indicate the need for immediate repair or rehabilitation of the culvert. 4.17.6.4.5 Cracks Cracks may be indicative of more serious underlying problems. The significance of these cracks will vary depending upon the type of culvert material, along with crack location, size and orientation. Cracks should be noted; monitored for propagation; and if warranted, evaluated for their effect on structural capacity. 1 4.17.6.4.6 Seams Seams, if present, must be inspected as they are critical to the culvert’s structural and hydraulic performance. Problem seams may allow loss of backfill, lead to infiltration/exfiltration of flow, affect structure performance, and should be evaluated for possible repair. 3 4.17.6.4.7 Joints Joints should be inspected for proper alignment and possible cracking. Misaligned joints contribute to loss of soil, infiltration/exfiltration of flow and other maintenance problems. Joint deficiencies should be noted and evaluated. 4 4.17.6.4.8 Undermining (Scour/Piping) Undermining/scour can occur at the exposed ends or footings of the culvert, as well as along the length of the culvert. Scour may be obvious during the visual inspection at the ends of the culvert. However, scour along the footings of arch culverts and piping may be less obvious. The extent of scour and resulting undermining should be determined and evaluated from a loss of support perspective. Appropriate repair measures to prevent future scour and to restore support to the culvert is essential. 4.17.6.4.9 End Treatment End treatment usually consists of headwalls, wingwalls, cut-off walls, toe-walls, slope protection, energy dissipators or flared end sections. Visual inspection of these items involves looking for cracks, misalignment, shifting or settling of headwalls or wingwalls, signs of scour, undermining or hydraulic piping. Any evidence of problems may require immediate repair to assure that the track subgrade remains stable. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-95 Roadway and Ballast 4.17.6.5 Baseline Measurements At the onset of a regular culvert inspection program, it is recommended that baseline measurements be taken for all culverts along the right-of-way. This information, in conjunction with the culvert inventory previously mentioned, will become valuable in the event difficulties are encountered. It is recommended that, where practical, the following information be recorded: a. Span b. Rise c. Skew angle d. Elevations at invert and crown along the conduit at least every 25 ft. e. Top of rail and top of subgrade elevations at centerline of culvert and centerline of track, and at 50-ft. and 100-ft. stations either side of the culvert. f. Length of culvert g. Distance from centerline of track to each end of the culvert h. Configuration and dimensions of headwalls, toe walls, wingwalls or other end treatments i. Differences in alignment, shape, materials, etc. along the culvert length j. Channel characteristics upstream and downstream k. Drainage area characteristics 4.17.6.6 Culvert Inspection Form Figure 1-4-28 represents a sample culvert inspection form that can be used by most railroad companies to inventory and assess existing culverts on their railroads. 4.17.7 EVALUATION/RECOMMENDED ACTION (2001) 4.17.7.1 Action Plan It will be up to the culvert inspector to notify the particular railroad’s engineering department of the nature and extent of the defects found. Depending on the conditions observed in the inspection of the culvert, an action plan must be developed. That course of action can come in several forms as noted below. 4.17.7.1.1 Speed Restrictions/Class Reduction It will be up to the culvert inspector to notify the appropriate railroad official if the condition of the pipe appears to be such that there is potential for subgrade instability, track settlement, or any track alignment irregularities that may warrant the need to reduce train speed. If such restriction is necessary, it must be placed immediately and should not be removed until the proper corrective action to stabilize the culvert, subgrade, and track structure has been completed. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-96 AREMA Manual for Railway Engineering Culverts 4.17.7.1.2 Monitoring Program The defects found may be such that no track or subgrade instability has occurred, and structural integrity and hydraulic performance of the culvert will be satisfactory. However, conditions observed may indicate potential deterioration and require establishing a plan for periodic monitoring of the culvert and the overlying track and subgrade conditions for the short or long term. It is recommended that appropriate measurements be taken as part of this monitoring program and compared against the measurements taken as part of the baseline measurements. It is important to note any localized distortions and deformations and to determine if these areas need further attention. The need for corrective action will be determined by conditions observed in the monitoring program and will be dependent upon the rate of change as evidenced by the measurements taken. 4.17.7.1.3 Rehabilitation In many situations, rehabilitation or repair of the existing culvert may be a viable option. Various means are available, depending upon the type and extent of the problems discovered. See Section 4.14 Culvert Rehabilitation. 4.17.7.1.4 Replacement Replacement of the culvert is necessary if a decision is made that rehabilitation is not an economical, structurally feasible, or hydraulically acceptable option. When replacement is indicated, proper intermediate steps must be taken to insure the stability and safety of the track structure. 4.17.8 INSPECTION FOLLOW-UP (2001) There should be a follow up procedure in effect to determine that any monitoring programs that have been set up to observe ongoing culvert conditions have been followed, and possibly to reevaluate the need to continue monitoring and/or perform a subsequent, complete inspection. Follow up for rehabilitation should be made to determine that the repairs that were made were sufficient to restore the structural integrity of the culvert and to provide the proper stability and support for the track structure and subgrade. If the culvert has been replaced, the follow up inspection should be made to determine that the replacement culvert was properly installed and the surrounding and adjacent soils properly compacted so that the culvert is operating properly, and the track structure is being properly supported. 1 3 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-97 Roadway and Ballast Figure 1-4-28. Culvert Inspection Form © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-98 AREMA Manual for Railway Engineering Culverts 1 3 4 Figure 1-4-28 Culvert Inspection Form (Continued) © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-99 Roadway and Ballast SECTION 4.18 PERFORATED PIPE DRAINS 4.18.1 GENERAL (2006) This portion of the Manual shall give guidance to constructing perforated pipe underdrains (or subdrains) with a granular filter. This work shall consist of furnishing and installing perforated pipe and porous backfill. Pipe underdrains shall have the nominal diameter specified, shall be placed in a trench to the established line and grade, and shall be backfilled as specified herein. 4.18.2 APPLICATIONS (2006) There are numerous types of applications for perforated pipe underdrains (or subdrains) in conjunction with railroad facilities. Grade crossings, lateral drains in the right of way installed parallel to the track, intermodal facilities, railroad yards, loading docks, bridge abutments, rock ledges and other narrow right of way constraints involving tight clearances are examples of situations possibly requiring underdrains. However, perforated pipe underdrains should not be used as a replacement for conventional ditch construction unless thorough site investigative work is conducted to insure adequate subgrade and ballast drainage. Loading situations vary at such sites – ranging from maintenance vehicles, highway legal loads, etc., up to E 80 and greater rail loads. Consideration must also be given to construction live loads. Vehicles used at intermodal facilities typically represent significant wheel loads that would influence the design of subdrain pipe. Suitable design methodology and installation standards must address intended use, loading, height of cover and pipe product characteristics. 4.18.3 MATERIALS (2006) Taking into consideration such factors as vehicle loads, cover depths, and product design requirements, pipe shall be of the type and size listed in the project specifications. Generally acceptable pipe materials (except as noted below) may include, but are not limited to, the following: 4.18.3.1 CORRUGATED POLYETHYLENE PIPE Shall conform to AASHTO M252 or AASHTO M294. 4.18.3.2 PROFILE WALL PVC PIPE Shall conform to AASHTO M304, ASTM F794 or F949. 4.18.3.3 CORRUGATED STEEL PIPE Shall conform to AASHTO M36, M190 Type A, M240, M245 or M246; ASTM A760, A762 or A845. 4.18.3.4 CORRUGATED ALUMINUM ALLOY PIPE Shall conform to M196; ASTM B745. 4.18.3.5 PVC/ABS COMPOSITE PIPE Shall conform to AASHTO M264; ASTM D2680. 4.18.3.6 PVC SOLID WALL PIPE Shall conform to AASHTO M278; ASTM D3034; F679, F758. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-100 AREMA Manual for Railway Engineering Culverts 4.18.3.7 ABS SOLID WALL PIPE Shall conform to ASTM D2751. 4.18.3.8 PERFORATED REINFORCED CONCRETE PIPE Shall conform to AASHTO M175; ASTM C444 Note – Not all the pipe products listed above are suitable under the anticipated loads (such as railroad live loads and construction traffic) for this application. The designer should check the loading conditions for the specific application at hand. Additionally, lateral edgedrain type products, addressed separately in Chapter 1, Part 10 of the Manual, may also be suitable pipe underdrain materials. 4.18.4 RELATED FILTER MATERIALS (2006) 4.18.4.1 GRANULAR FILTER MATERIALS It is recommended that a granular filter material consist of a washed, well-graded, angular material that provides necessary pipe support while retaining free drainage characteristics. Generally the ballast used beneath the track structure is suitable for this purpose. Pipe perforation geometry (i.e., opening size and shape) should be considered when specifying minimum gradation of filter material. 4.18.4.2 FILTER FABRIC 1 Filter fabrics shall conform to the requirements stated in Chapter 1, Part 10 of this Manual. 4.18.5 HYDRAULIC DESIGN (2006) a. b. The hydraulic design of the subsurface drainage system begins with determining the flow. This is accomplished using a combination of analytical and empirical methods as required. Field investigations should include soil and geological studies, borings to find the elevation and extent of the water table, and measurements of the groundwater discharge. The investigation should be thorough and ideally conducted during the rainy season or during snowmelt if the region has snow cover. It may involve digging a trench to aid in estimating flow. After the design flow is established, the underdrain piping may be sized per the resultant unit inflow and available outlet locations. The following conditions apply to the design of the subsurface drainage system: (1) Outlets for the underdrain system should be provided for at intervals preferably not exceeding 1000 feet. Outlets may be run into a storm drainage system or natural waterway, depending upon local regulations. (2) Pipe underdrains should be placed on grades steeper than 0.5% if possible. Minimum grades of 0.2% are acceptable. (3) The depth of the underdrain will depend on the permeability of the soil, the elevation of the water table, and the amount of drawdown necessary to achieve stability. (4) The hydraulic design analysis should be made in accordance with ANSI/ASCE 12-92 “Standard Guidelines for the Design of Urban Subsurface Drainage,” as well as applicable portions of this Manual. (5) Due to concerns for clogging, a minimum of 12-inch diameter should be considered for all newly installed underdrains. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-101 3 4 Roadway and Ballast 4.18.6 STRUCTURAL DESIGN (2006) Due to the wide variety of applications for perforated pipe underdrain systems within and/or adjacent to railroad subgrades, careful consideration should be given to the pipe material and installation method chosen. Figure 1-429 shows a typical subdrain installed parallel to the track and below the subballast. Consideration should be given to the railroad live load influence zone to determine the installation requirements and pipe material selection for the intended application. In addition, the dead load of the soil or ballast material above the pipe must be taken into consideration. If the installation is beyond the limits of the influence zone, consideration should be given to any potential live load effects from vehicles and maintenance of way equipment that may operate above the completed underdrain system. Underdrains installed perpendicular to the track should be installed using the same criteria as contained elsewhere within this Manual. Figure 1-4-29. Typical Underdrain Detail 4.18.7 CONSTRUCTION REQUIREMENTS (2006) The recommended construction method for a typical subdrain installation shall be as follows: 4.18.7.1 EXCAVATION Trench excavation shall be of such dimensions as to provide ample room for construction. Trench widths shall be at least 12 inches wider than the outside diameter of the pipe (6-inches either side of the pipe). The bottom of the trench, in so far as is practical, shall be excavated to permit proper placement of the pipe. The excavation for the underdrain shall include the removal of any obstructions encountered. Unless otherwise required, the trench shall be excavated to a depth at least 3 inches below the outside bottom elevation of the planned underdrain. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-102 AREMA Manual for Railway Engineering Culverts 4.18.7.2 FILTER FABRIC PLACEMENT The underdrain trench shall be lined with filter fabric. The fabric shall be in intimate contact with the trench and the bottom of the trench as shown in Figure 1-4-29. 4.18.7.3 SUBGRADE AND FOUNDATION PROPERTIES Site preparation should be in accordance with the contract plans and specifications. Bedding for subsurface drainage systems should be as specified and completed to the design line and grade. The pipe shall be laid on bedding fill shaped to fit the pipe throughout its entire length. The intrusion of foreign material into any portion of the drainage system due to construction and weather events should be prevented until the system is adequately protected by backfill. When necessary, all excavations should be dewatered prior to and during installation and backfilling of the system. 4.18.7.4 LAYING PIPE a. The pipe shall be laid true to line and grade with close fitting joints. Joining systems should be “soil tight.” Joints may be split coupler bands, bell-bell couplers, bell and spigot, or other equally effective joining systems recommended by the pipe manufacturer. Selection of the allowable configuration of joint shall be as per the site demands (i.e., steep slopes for the outlet piping would demand a restraining joint system such as the split coupler band which engages the exterior corrugations of the pipe wall). b. Lateral connections shall be made with suitable branch fittings (i.e., tees, wyes, etc.). The upper ends of the pipe underdrains shall be closed with plugs or endcaps. All appurtenances to the underdrain piping should be as per the pipe manufacturer’s recommendation for the proposed loading condition. When the total connected length of the underdrain piping exceeds the limits of available maintenance equipment, clean out points should be incorporated for maintenance purposes and located at a maximum of 500 feet apart. c. Perforated pipe shall be so laid that the perforations are in the bottom half of the pipe (the invert). Where perforated pipe installations outlet into open ditches, a minimum of 8 feet of pipe from the outlet shall be non-perforated. Pipe discharge outlets shall be constructed concurrently with the underdrains. Design and construction details must consider proper protection of the exposed ends of the pipe. 1 3 4.18.7.5 BACKFILLING a. b. After the pipe has been placed, the granular filter material shall be placed for the full width of the trench around the pipe and shall extend to the bottom of the ballast. Granular backfill is to be placed in a balanced fashion in maximum loose lifts of 6-10 inches and compacted per the project’s requirements. Compaction equipment must be of the type and size so as not to damage the pipe. The area above the trench shall be filled with ballast and compacted to match the ballast profile. (See Figure 1-4-29.) The pipe underdrains require adequate minimum cover to protect the pipe from vehicle loads – both temporary construction loads and long-term design loads. Minimum cover heights required must take into account the type of pipe, vehicle load, and quality of the backfill. Suitable minimum cover limits should be established in the project specifications. 4.18.8 INSPECTION AND ACCEPTANCE (2006) 4.18.8.1 RECEIVING AND STORING OF MATERIALS All construction materials must be carefully and thoroughly inspected prior to and during placement. Shipments of select fill materials and drainage products should be accompanied by certified test reports as required. All drainage products or drainage system components should be measured to check size, shape, and fit. All materials must be inspected to ensure that they are free of foreign deposits, defects, and damage. Repairs may be performed on © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-4-103 4 Roadway and Ballast damaged goods following inspection and approval of the owner and/or project engineer and after consultation with the manufacturer. Such repairs must follow applicable specifications and accepted industry standards. Materials should be stored to avoid damage. Observance of any special handling methods required shall be verified and recorded. The inspector is responsible for monitoring the contractor’s observance of these requirements. 4.18.8.2 CONSTRUCTION INSPECTION All phases of the installation of the underdrain systems and any related products should be inspected to ensure that all materials are installed per the manufacturer’s standards and the project specifications. The installation should be monitored for proper line, grade and joint integrity. Select backfill material shall conform to project specifications and the proper placement and compaction of this fill material must be verified. 4.18.8.3 FINAL INSPECTION AND ACCEPTANCE Prior to acceptance, the underdrain system should be inspected. Final inspection may be by means of a closed circuit television or other acceptable verification method used to supplement the “as-built” drawings of the underdrain system and to assure that the system was constructed properly. 4.18.9 OPERATION AND MAINTENANCE (2006) The design engineer or other so qualified individual should prepare an operations and maintenance plan. Guidance in preparing such a plan can be found in ASCE 14-93 “Standard Guidelines for Operation and Maintenance of Urban Subsurface Drainage.” 4.18.10 SAFETY PROVISIONS (2006) Individual railroads may require specific precautions as deemed advisable to insure the safety of the trains, tracks and construction workers throughout the perforated pipe underdrain installation process, particularly when installed adjacent to live track. Regardless of the installation methods chosen, the track must be adequately supported during construction. All procedures involved in the installation must comply with applicable guidelines and regulations, including FRA and OSHA requirements. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-4-104 AREMA Manual for Railway Engineering 118 Part 5 Pipelines1 — 2008 — PREAMBLE The position of the Association is that the encasement of pipelines transporting liquids under pressure across, over, or under a railroad operating right-of-way, or that railroad right-of-way proposed for future operations, is in the best interest of the railroad, public, and parties contracting for the crossing. The encasement, when installed in accordance with the recommended practice of the Association, permits the pipeline operating company to install a facility of usual design, at or near, a usual depth of cover or a usual overhead clearance requirement. Installation of the encasement pipe prior to pipeline construction activities reduces the risk of delay caused by encountering unanticipated facilities, poor subsurface conditions, or difficult attachment at the crossing location. 1 The encasement affords the pipeline and railroad companies a measure of protection from damage to their operating facilities resulting from the actions of unauthorized parties, or the errant actions of authorized parties. Additionally, it shields the pipeline from potential physical damage as a result of derailment, thus reducing the risk of product loss in the surrounding soil and promoting the earliest possible safe return to operation of the pipeline facility. By conducting the flow of lost product to the outer limits of the railroad operating right-of-way, the risk of delay or curtailment of railroad operations during repair and cleanup activities is reduced. Allowing both the railroad and pipeline companies to resume safe operation of their facilities as quickly as possible following an event serves the interests of the public, the railroad, and the pipeline company. 3 The Association supports research for engineered encasements that allow cathodic protection and railroad service protection. TABLE OF CONTENTS Section/Article Description 5.1 Specifications for Pipelines Conveying Flammable Substances . . . . . . . . . . . . . . . . . . 5.1.1 Scope (1993) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.2 General Requirements (2002). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.3 Steel Carrier Pipe (2002). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.4 Plastic Carrier Pipe Conveying Non Liquid Flammable Substances (2002) . . . . . . . . . . . 1 Page 1-5-3 1-5-3 1-5-4 1-5-5 1-5-6 References, Vol. 34, 1933, p. 163, 830; Vol. 42, 1941, pp. 555, 831; Vol 43, 1942, pp. 481, 731; Vol. 54, 1953, pp. 1089, 1385; Vol. 55, 1954, pp. 692, 1054; Vol. 56, 1955, pp. 688, 1115; Vol. 57, 1956, pp. 645, 1077; Vol. 62, 1961, pp. 692, 938; Vol. 63, 1962, pp. 582, 750; Vol. 65, 1964, pp. 491, 835; Vol. 67, 1966, pp. 527, 739; Vol. 72, 1971, p. 109; Vol. 73, 1972, p. 150; Vol. 92, 1991, p. 39; Vol. 94, p. 42. Latest page consist: 1 to 19 incl. (1993). © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-1 Roadway and Ballast TABLE OF CONTENTS (CONT) Section/Article 5.1.5 5.1.6 5.1.7 5.1.8 Description Page Casing Pipe (2002) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Construction (2002) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Approval of Plans (2002) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Execution of Work (1993). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5-7 1-5-8 1-5-10 1-5-11 5.2 Specifications for Uncased Gas Pipelines within the Railway Right-of-Way. . . . . . . . 5.2.1 Scope (1993) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.2 General Requirements (2002) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.3 Carrier Pipe (2002) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.4 Construction (1993) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.5 Approval of Plans (2002) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.6 Execution of Work (1993). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.7 Commentary (1993) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5-11 1-5-11 1-5-12 1-5-13 1-5-21 1-5-22 1-5-22 1-5-22 5.3 Specifications for Pipelines Conveying Non-Flammable Substances . . . . . . . . . . . . . . 5.3.1 Scope (1993) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.2 General Requirements (2002) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.3 Carrier Pipe (2002) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.4 Steel Casing Pipe (2002). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.5 Construction (2002) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.6 Approval of Plans (1993) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.7 Execution of Work (1993). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5-23 1-5-23 1-5-23 1-5-24 1-5-25 1-5-27 1-5-28 1-5-29 5.4 Specifications for Overhead Pipelines Crossings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.2 General Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.3 General Design Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.4 Structural Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.5 Inspection and Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5-29 1-5-29 1-5-29 1-5-29 1-5-30 1-5-31 5.5 Specifications for Fiber Optic “Route” Construction on Railroad Right of Way . . . . 5.5.1 Scope (2001) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5.2 Planning (2001) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5.3 Design (2001) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5.4 Construction (2001) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5.5 Documentation (2001) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5.6 Maintenance (2001) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5.7 Definitions (2001) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5.8 Abbreviations (2001) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5.9 Appendix (2001) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5-31 1-5-31 1-5-32 1-5-32 1-5-37 1-5-40 1-5-41 1-5-42 1-5-45 1-5-46 LIST OF FIGURES Figure 1-5-1 1-5-2 1-5-3 Description Page Casing Pipe Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Uncased Gas Pipelines Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Casing Pipe Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5-5 1-5-12 1-5-23 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-2 AREMA Manual for Railway Engineering Pipelines LIST OF FIGURES (CONT) Figure 1-5-4 1-5-5 1-5-6 1-5-7 1-5-8 1-5-9 1-5-10 1-5-11 1-5-12 1-5-13 Description Page Methodology for Equating Fiber Optic Cable Locations to Railroad Track & Right-of-Way Maps1-5-47 Bridge Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5-48 Cable Depth Around Culverts and Ditches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5-49 Bore Pit Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5-50 Regen Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5-52 Conventional Fill Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5-53 Standard Turnout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5-55 General Shoring Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5-56 Fill Installation Directional Bore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5-57 Installation on Top of Cut . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5-58 LIST OF TABLES Table 1-5-1 1-5-2 1-5-3 1-5-4 1-5-5 1-5-6 Description Minimum Wall Thickness for Steel Casing Pipe for E80 Loading . . . . . . . . . . . . . . . . . . . . . . . Plan Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Minimum Nominal Wall Thickness (in.) for Uncased Carrier Pipe . . . . . . . . . . . . . . . . . . . . . . Plan Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Minimum Wall Thickness for Steel Casing Pipe for E80 Loading . . . . . . . . . . . . . . . . . . . . . . . Plan Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 1-5-7 1-5-11 1-5-14 1-5-22 1-5-26 1-5-28 SECTION 5.1 SPECIFICATIONS FOR PIPELINES CONVEYING FLAMMABLE SUBSTANCES 1 3 5.1.1 SCOPE (1993) These specifications cover minimum requirements for pipelines installed on or adjacent to railway rights-of-way to carry liquid flammable products or highly volatile substances under pressure. The term “engineer” used herein means the chief engineer of the railway company or the authorized representative. These specifications may be increased when risks from any of the following conditions are increased: a. Track speed. b. Traffic density. c. Traffic sensitivity. d. Terrain conditions, cuts/fills, etc. e. Curvature and grade. f. Bridges and other structures. g. Pipe size, capacity and material carried. h. Environmental risks/damages. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-3 4 Roadway and Ballast 5.1.2 GENERAL REQUIREMENTS (2002) a. Pipelines under railway tracks and across railway rights-of-way shall be encased in a larger pipe or conduit called the casing pipe as indicated in Figure 1-5-1. Except for plastic carrier pipe, casing pipe may be omitted in the following locations: (1) Under secondary or industry tracks as approved by the engineer. (2) On pipelines in streets where the stress in the pipe from internal pressure and external loads does not exceed 40 percent of the specified minimum yield strength (multiplied by longitudinal joint factor) of the steel pipe material, as approved by the engineer. (3) On gas pipelines as provided in Section 5.2. b. Pipelines shall be installed under tracks by boring or jacking, if practicable. c. Pipelines shall be located, where practicable, to cross tracks at approximately right angles thereto but preferably at not less than 45 degrees and shall not be placed within a culvert, under railway bridges nor closer than 45 ft. to any portion of any railway bridge, building or important structure, except in special cases and then by special design as approved by the engineer. d. Pipelines carrying flammable substances shall, where practicable, cross any railway where tracks are carried on an embankment. e. Emergency response procedures should be developed to handle a situation in which a pipeline leak or railroad derailment or incident may jeopardize the integrity of the pipeline. Local conditions should be considered when developing these procedures. f. Where laws or orders of public authority prescribe a higher degree of protection than specified herein, then the higher degree of protection so prescribed shall be deemed a part of these specifications. Note 1: See Article 5.1.3 Note 2: See Article 5.1.4 Note 3: See Article 5.1.6.2 Note 4: See Article 5.1.6.4 Note 5: See Article 5.1.6.5 Figure 1-5-1. Casing Pipe Installation g. Pipelines and casing pipe shall be suitably insulated from underground conduits carrying electric wires on railway rights-of-way. All pipelines, except those in streets, shall be prominently marked at the rights-of-way (on both sides of track for undercrossings) by signs substantially worded thus: “High pressure…main…in vicinity. Call…” © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-4 AREMA Manual for Railway Engineering Pipelines h. Additional signing may be required by the engineer where above signs are not readily visible from the track. 5.1.2.1 Pipeline Inspection and Maintenance a. Pipeline owners engaged in the transport of liquid flammable or highly volatile substances are subject to regulations of the Federal Government. These regulationsrequire certain inspection routines that, in the general case, are conducted from within the carrier pipe or by non-destructive methods not requiring it be exposed. b. It is the responsibility of the pipeline owner to conduct the necessary inspections without interference to the operations of the Railway Company. Should it become necessary to expose a pipe for an inspection, or for its replacement, the owner shall design a procedure that does not interfere with Railway operations, and shall make prior arrangements with the Railway as may be necessary to permit safe conduct of the work. c. Pipeline maintenance shall be limited to the installation of a new carrier pipe in an existing casing, renewal of carrier and casing pipe separators or the installation of a new crossing. In all cases, the work shall be conducted in the same manner as in the installation of a new crossing, which is subject to the requirements of these specifications. Casings abandoned or replaced by new location work shall be backfilled by methods and materials as directed by the Engineer. The location of abandoned facilities shall be recorded and records maintained by the pipeline owner. d. The owners of pipelines not subject to regulation requiring inspection are expected to inspect their facilities as a matter of due diligence in the conduct of its business. The Railway may, as a right but not a duty, require an inspection of the construction, to include receiving a written report of findings certified by a registered professional engineer. Maintenance of these facilities shall be conducted as above described. 1 5.1.3 STEEL CARRIER PIPE (2002) a. Pipelines carrying oil, liquefied petroleum gas and other flammable liquid products shall be of steel and conform to the requirements of the current ANSI B 31.4 Liquid Transportation Systems for Hydrocarbons, Liquid Petroleum Gas, Anhydrous Ammonia, and Alcohols, and other applicable ANSI codes, except that the maximum allowable stresses1 for design of steel pipe shall not exceed the following percentages of the specified minimum yield strength (multiplied by longitudinal joint factor) of the pipe as defined in the above codes. b. Requisites for steel carrier line pipe under railway tracks shall apply for a minimum distance of 50 ft. (measured at right angles) from centerline of outside tracks or 2 ft. beyond toe of slope or 25 ft. beyond the ends of casing (when casing is required), whichever is greater. c. The pipe shall be laid with sufficient slack so that it is not in tension. 4 5.1.3.1 Allowable Hoop Stress Due to Internal Pressure 5.1.3.1.1 With Casing Pipe The following percentages apply to hoop stress in steel pipe within a casing under railway tracks and across railway rights-of-way: 1 a. Seventy-two percent on oil pipelines. b. Fifty percent for pipelines carrying condensate, natural gasoline, natural gas liquids, liquefied petroleum gas, and other liquid petroleum products. c. Sixty percent for gas pipelines. If the maximum allowable stress in the carrier pipe on either side of the crossing is less than specified above, the carrier pipe at the crossing shall be designed at the same stress as the adjacent carrier pipe. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 3 1-5-5 Roadway and Ballast 5.1.3.1.2 Without Casing Pipe The following percentages apply to hoop stress in steel pipe without a casing under secondary or industry tracks: a. Sixty percent for oil pipelines. b. Forty percent for pipelines carrying condensate, natural gasoline, natural gas liquids, liquefied petroleum gas, and other liquid petroleum products. c. For gas pipelines see Section 5.2. 5.1.3.1.3 On Right-of-Way The following percentages apply to hoop stress in steel pipe laid longitudinally on railway rights-of-way: a. Sixty percent for oil pipelines. b. Forty percent for pipelines carrying condensate, natural gasoline, natural gas liquids, liquefied petroleum gas, and other liquid petroleum products. c. For gas pipelines see Section 5.2. 5.1.4 PLASTIC CARRIER PIPE CONVEYING NON LIQUID FLAMMABLE SUBSTANCES (2002) a. Plastic carrier pipelines shall be encased according to Article 5.1.5. b. Plastic carrier pipe material includes thermoplastic and thermoset plastic pipes. Thermoplastic types include Polyvinyl Chloride (PVC), Acrylonitrile Butadiene Styrene (ABS), Polyethylene (PE), Polybutylene (PB), Cellulose Acetate Butyrate (CAB) and Styrene Rubber (SR). Thermoset types include Reinforced Plastic Mortar (RPM), Reinforced Thermosetting Resin (FRP) and Fiberglass Reinforced Plastic (FRP). c. Plastic pipe material shall be resistant to the chemicals with which contact can be anticipated. Plastic carrier pipe shall not be utilized where there is potential for contact with petroleum contaminated soils or other non-polar organic compounds that may be present in surrounding soils. d. Plastic carrier pipe can be utilized to convey flammable gas products provided the pipe material is compatible with the type of product conveyed and the maximum allowable operating pressure is less than 100 psi. Carrier pipe materials, design and installation shall conform to Code of Federal Regulation 49 CFR Part 178 to 199, specifically Part 192 and American National Standards Institute (ANSI) B31.3 and B31.8 and ASTM D2513. Codes, specifications and regulations current at time of constructing the pipeline shall govern the installation of the facility within the railway rights-of-way. The proof testing of the strength of carrier pipe shall be in accordance with ANSI requirements. Plastic carrier pipelines will be encased according to Article 5.1.5. 5.1.5 CASING PIPE (2002) a. Casing pipe and joints shall be of steel and of leakproof construction, capable of withstanding railway loading. The inside diameter of the casing pipe shall be large enough to allow the carrier pipe to be removed subsequently without disturbing the casing pipe. All joints or couplings, supports, insulators or centering devices for the carrier pipe within a casing under railroad tracks shall be taken into account. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-6 AREMA Manual for Railway Engineering Pipelines b. When casing is installed without benefit of a protective coating or said casing is not cathodically protected, the wall thickness shall be increased to the nearest standard size which is a minimum of 0.063 in. greater than the thickness required except for diameters under 12-3/4 in. Table 1-5-1. Minimum Wall Thickness for Steel Casing Pipe for E80 Loading When coated or cathodically protected Nominal Thickness (inches) When not coated or cathodically protected Nominal Thickness (inches) 12-3/4 and under 0.188 0.188 14 0.188 0.250 16 0.219 0.281 18 0.250 0.312 20 and 22 0.281 0.344 24 0.312 0.375 26 0.344 0.406 28 0.375 0.438 30 0.406 0.469 32 0.438 0.500 34 and 36 0.469 0.531 38 0.500 0.562 40 0.531 0.594 42 0.562 0.625 44 and 46 0.594 0.656 48 0.625 0.688 50 0.656 0.719 52 0.688 0.750 54 0.719 0.781 56 and 58 0.750 0.812 60 0.781 0.844 62 0.812 0.875 64 0.844 0.906 66 and 68 0.875 0.938 70 0.906 0.969 72 0.938 1.000 Nominal Diameter (inches) 1 3 4 5.1.5.1 Steel Casing Pipe Steel pipe shall have a specified minimum yield strength, SMYS, of at least 35,000 psi. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-7 Roadway and Ballast 5.1.5.2 Flexible Casing Pipe For flexible casing pipe, a maximum vertical deflection of a casing pipe of 3 percent of its diameter plus 1/2 in. clearance shall be provided so that no loads from the roadbed, track, traffic or casing pipe itself are transmitted to the carrier pipe. When insulators are used on the carrier pipe, the inside diameter of flexible casing pipe shall be at least 2 in. greater than the outside diameter of the carrier pipe for pipe less than 8 in. in diameter; at least 3-1/4 in. greater for pipe 8 in. to 16 in., inclusive, in diameter and at least 4-1/2 in. greater for pipe 18 in. in diameter and over. Flexible pipe must be able to be electronically located. 5.1.5.3 Length of Casing Pipe Casing pipe under railway tracks and across railway rights-of-way shall extend to the greater of the following distances, measured at right angles to centerline of track. If additional tracks are constructed in the future or if the railway determines that the roadbed should be widened, the casing shall be extended or other special design incorporated: a. 2 ft. beyond toe of slope. b. 3 ft. beyond ditch. c. A minimum distance of 25 ft. each side from centerline of outside track when casing is sealed at both ends. d. A minimum distance of 45 ft. each side from centerline of outside track when casing is open at both ends. e. Plastic carrier pipe conveying flammable substances shall be encased the entire limits of the right-of-way. If special conditions exist which prevent encasement within the entire limits of the right-of-way, the minimum encased lengths must be approved by the engineer. 5.1.6 CONSTRUCTION (2002) a. Casing pipe shall be so constructed as to prevent leakage of any substance from the casing throughout its length, except at ends of casing where ends are left open, or through vent pipes when ends of casing are sealed. Casing shall be so installed as to prevent the formation of a waterway under the railway, and with an even bearing throughout its length, and shall slope to one end (except for longitudinal occupancy). b. Where casing and/or carrier pipe is cathodically protected, the engineer shall be notified and a suitable test made to ensure that other railway structures and facilities are adequately protected from the cathodic current in accordance with the recommendation of current Reports of Correlating Committee on Cathodic Protection, published by the National Association of Corrosion Engineers. 5.1.6.1 Method of Installation a. Installations by open-trench methods shall comply with Part 4, Culverts, Section 4.12, Assembly and Installation of Pipe Culverts, of this Chapter. b. Bored or jacked installations shall have a bored hole diameter essentially the same as the outside diameter of the pipe plus the thickness of the protective coating. If voids should develop or if the bored hole diameter is greater than the outside diameter of the pipe (including coating) by more than approximately 1 in., remedial measures as approved by the engineer shall be taken. Boring operations shall not be stopped if such stoppage would be detrimental to the railway. c. Tunneling operations shall be conducted as approved by the engineer. If voids are caused by the tunneling operations, they shall be filled by pressure grouting or by other approved methods which will provide proper support. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-8 AREMA Manual for Railway Engineering Pipelines 5.1.6.2 Depth of Installation 5.1.6.2.1 Casing Pipe Casing pipe under railway tracks and across railway rights-of-way shall be not less than 5-1/2 ft. from base of railway rail to top of casing at its closest point, except that under secondary or industry tracks this distance may be 4-1/2 ft. On other portions of rights-of-way where casing is not directly beneath any track, the depth from ground surface or from bottom of ditches to top of casing shall not be less than 3 ft. 5.1.6.2.2 Carrier Pipe Steel carrier pipe installed under secondary or industry tracks without benefit of casing shall be not less than 10 ft. from base of railway rail to top of pipe at its closest point nor less than 6 ft. from ground surface or from bottom of ditches. Plastic carrier pipe must be encased under secondary or industry tracks within the limits of the right-ofway. 5.1.6.3 Inspection and Testing ANSI Codes current at time of constructing the pipeline, shall govern the inspection and testing of the facility within the railway rights-of-way except as follows: a. One-hundred percent of all steel pipe field welds shall be inspected by radiographic examination, and such field welds shall be inspected for 100 percent of the circumference. b. The proof testing of the strength of carrier pipe shall be in accordance with ANSI requirements. 1 5.1.6.4 Seals a. Where ends of casing are below ground they shall be suitably sealed. b. Where ends of casing are at or above ground surface and above high-water level they may be left open, provided drainage is afforded in such manner that leakage will be conducted away from railway tracks or structure. Where proper drainage is not provided, the ends of casing shall be sealed. 3 5.1.6.5 Vents Casing pipe, when sealed, shall be properly vented. Vent pipes shall be of sufficient diameter, but in no case less than 2 in. in diameter, shall be attached near end of casing and project through ground surface at right-of-way lines or not less than 45 ft. (measured at right angles) from centerline of nearest track. Vent pipe, or pipes, shall extend not less than 4 ft. above ground surface. Top of vent pipe shall be fitted with down-turned elbow properly screened, or a relief valve. Vents in locations subject to high water shall be extended above the maximum elevation of high water and shall be supported and protected in a manner that meets the approval of the engineer. Vent pipes shall be no closer than 4 ft. (vertically) from aerial electric wires. 5.1.6.6 Shut-Off Valves Accessible emergency shut-off valves shall be installed within effective distances each side of the railway as mutually agreed to by the engineer and the pipeline company. These valves should be marked with signs for identification. Where pipelines are provided with automatic control stations at locations and within distances approved by the engineer, no additional valves shall be required. 5.1.6.7 Longitudinal Pipelines Longitudinal pipelines should be located as far as possible from any track. They must not be within 25 ft. of any track and must have a minimum of 6 ft. ground cover over the pipeline up to 50 ft., measured from the track centerline. Where pipeline is laid more than 50 ft. from centerline of track, minimum cover shall be at least 5 ft. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-9 4 Roadway and Ballast Pipelines must be marked by a sign approved by the engineer every 500 ft. and at every road crossing, streambed, other utility crossing, and at locations of major change in direction of the line. Longitudinal carrier pipeline shall be steel. Plastic carrier pipe may be utilized for longitudinal installation with approval by the engineer, but shall be encased within the limits of the right-of-way. Casing may be omitted with approval of the engineer, provided that minimum burial depth is increased to comply with the most conservative requirements of either: the engineer’s instructions, current ANSI specifications, current OSHA regulations, or local regulatory agency specifications. 5.1.7 APPROVAL OF PLANS (2002) a. Plans for proposed installation shall be submitted to and meet the approval of the engineer before construction is begun. b. Plans shall be drawn to scale showing the relation of the proposed pipeline to railway tracks, angle of crossing, location of valves, railway survey station, right-of-way lines and general layout of tracks and railway facilities. Plans should also show a cross section (or sections) from field survey, showing pipe in relation to actual profile of ground and tracks. If open-cutting or tunneling is necessary, details of sheeting and method of supporting tracks or driving tunnel shall be shown. c. In addition to the above, plans should contain the following data: © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-10 AREMA Manual for Railway Engineering Pipelines Table 1-5-2. Plan Data Carrier Pipe Casing Pipe Contents to be handled Outside Diameter Pipe Material Specification and grade Wall thickness Actual Working pressure Type of joint Coating Method of installation Vents: Number: Size: Seals: Both ends: Height above ground: One end: Type: Bury: Base of rail to top of casing: Bury: (Not beneath tracks) ft. in. ft. Bury: (Roadway ditches) ft. 1 in. in. Type, size and spacing of insulators or supports: Distance C.L. track to face of jacking/receiving pits ft. in. Bury: Base of rail to bottom jacking/receiving pits ft. in. Cathodic protection: Yes No 3 5.1.8 EXECUTION OF WORK (1993) 4 The execution of work on railway rights-of-way, including the supporting of tracks, shall be subject to the inspection and direction of the engineer. SECTION 5.2 SPECIFICATIONS FOR UNCASED GAS PIPELINES WITHIN THE RAILWAY RIGHT-OF-WAY 5.2.1 SCOPE (1993) These specifications cover minimum specifications for pipelines installed on or adjacent to railway rights-of-way to carry flammable and nonflammable gas products which, from their nature or pressure, might cause damage if escaping on or in the vicinity of railway property. The term “engineer” as used herein means the chief engineer of © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-11 Roadway and Ballast the railway company or the authorized representative. These specifications may be increased when risks from any of the following conditions are increased: a. Track Speed. b. Traffic density. c. Traffic sensitivity. d. Terrain conditions, cuts/fills, etc. e. Curvature and grade. f. Bridges and other structures. g. Pipe size, capacity and material carried. h. Environmental risks/damages. 5.2.2 GENERAL REQUIREMENTS (2002) a. Pipelines shall be installed under tracks by boring or jacking, if practicable. b. Pipelines shall be located, where practicable, to cross tracks at approximately 90 degrees but not less than 45 degrees, and shall not be placed within a culvert, under railway bridges, nor closer than 45 ft. to any portion of any railway bridge, building or other important structure, except in special cases and then by special design as approved by the engineer. c. Pipelines carrying flammable gas products shall, where practicable, cross any railway where tracks are carried on an embankment. d. Emergency response procedures should be developed to handle a situation in which a pipeline leak or railroad derailment or incident may jeopardize the integrity of the pipeline. Local conditions should be considered when developing these procedures. e. Uncased gas pipelines under railroad track and on right-of-way shall be installed as indicated in Figure 1-52. Note 1: See Article 5.2.3.2 Note 2: See Article 5.2.4.2 Figure 1-5-2. Uncased Gas Pipelines Installation f. Where laws or orders of public authority prescribe a higher degree of protection than specified herein, then the higher degree of protection so prescribed shall be deemed a part of these specifications. g. Pipelines and casing pipe shall be suitably insulated from underground conduits carrying electric wires on railway rights-of-way. All pipelines, except those in streets, shall be prominently marked at the rights-of-way (on both sides of track for undercrossings) by signs substantially worded thus: “High pressure…main…in vicinity. Call…” © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-12 AREMA Manual for Railway Engineering Pipelines h. Additional signing may be required by the engineer where above signs are not readily visible from the track. 5.2.2.1 Pipeline Inspection and Maintenance a. Pipeline owners engaged in the transport of flammable and non-flammable gas products are subject to regulations of the Federal Government. These regulations require certain inspection routines that, in the general case, are conducted from within the carrier pipe or by non-destructive methods not requiring it be exposed. b. It is the responsibility of the pipeline owner to conduct the necessary inspections without interference to the operations of the Railway Company. Should it become necessary to expose a pipe for an inspection, or for its replacement, the owner shall design a procedure that does not interfere with Railway operations, and shall make prior arrangements with the Railway as may be necessary to permit safe conduct of the work. c. Pipeline maintenance shall be limited to the installation of a new carrier pipe at a new crossing location, which is subject to the requirements of these specifications. Carrier pipes abandoned by new location work shall be backfilled by methods and materials as directed by the Engineer. The location of abandoned facilities shall be recorded and records maintained by the pipeline owner. d. The owners of pipelines not subject to regulation requiring inspection are expected to inspect their facilities as a matter of due diligence in the conduct of its business. The Railway may, as a right but not a duty, require an inspection of the construction, to include receiving a written report of findings certified by a registered professional engineer. Maintenance of these facilities shall be conducted as above described. 5.2.3 CARRIER PIPE (2002) 1 a. Pipelines carrying flammable and nonflammable gas products shall be of steel and shall conform to the requirements of the current ANSI B 31.8 Gas Transmission and Distribution Piping Systems, and other applicable ANSI codes. b. Carrier line pipe construction shall be approved by the engineer. Joints for carrier line pipe must be of an approved welded type. Steel pipe must have a specified minimum yield strength, SMYS, of at least 35,000 psi. The nominal wall thickness for the steel carrier pipe, specified minimum yield strength, SMYS, maximum allowable operating pressure, MAOP, and outside pipe diameter, D, are given in Table 1-5-3. c. 3 These Table 1-5-3 wall thicknesses are based on four design criteria. These design criteria consider: (1) The maximum allowable hoop stress due to internal pressure as specified in regulatory codes; (2) The maximum combined multiaxial stress due to external and internal loads; 4 (3) Fatigue in girth welds due to external live loads; (4) Fatigue in longitudinal seam welds due to external live loads. d. The greatest wall thickness resulting from each of the design conditions are shown in Table 1-5-3. e. Design parameter assumptions used to calculate the Table 1-5-3 wall thicknesses are as follows: • Depth of carrier from base of rail is 10 ft. • Double Track condition is assumed. • Modulus of Soil Reaction E´ = 500 psi. • Soil Resilient Modulus Er = 10,000 psi. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-13 Roadway and Ballast • Girth weld is located at centerline of track. • Overbore of 2" over pipe diameter during installation. • Class location design factor F = 0.6 used in design criterion paragraph c(1) given above. • Factor of Safety FS = 1.5 used in design criteria b, c, and d given above. f. See “Design of Uncased Pipeline at Railroad Crossings” as referenced in Article 5.2.7 for additional details on the design parameters used to determine the wall thickness. g. If actual crossing conditions fall outside these parameters, tending to require a thicker walled pipe, a detailed analysis must be performed using the design methodology referenced in Article 5.2.7. Design calculations must be provided for railroad review when conditions outside those above are present. Table 1-5-3. Minimum Nominal Wall Thickness (in.) for Uncased Carrier Pipe D (in.) SMYS (psi) 35000 42000 52000 SMYS (psi) 60000 70000 35000 MAOP < 100 psi 42000 52000 60000 70000 MAOP < 200 psi < 18.0 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 20.0 0.219 0.219 0.219 0.219 0.219 0.219 0.219 0.219 0.219 0.219 22.0 0.226 0.226 0.226 0.226 0.226 0.226 0.226 0.226 0.226 0.226 24.0 0.250 0.250 0.250 0.250 0.250 0.250 0.250 0.250 0.250 0.250 26.0 0.281 0.281 0.281 0.281 0.281 0.281 0.281 0.281 0.281 0.281 28.0 0.281 0.281 0.281 0.281 0.281 0.312 0.281 0.281 0.281 0.281 30.0 0.312 0.312 0.312 0.312 0.312 0.344 0.312 0.312 0.312 0.312 32.0 0.344 0.344 0.344 0.344 0.344 0.344 0.344 0.344 0.344 0.344 34.0 0.344 0.344 0.344 0.344 0.344 0.406 0.344 0.344 0.344 0.344 36.0 0.375 0.375 0.375 0.375 0.375 0.406 0.375 0.375 0.375 0.375 38.0 0.406 0.406 0.406 0.406 0.406 0.438 0.406 0.406 0.406 0.406 40.0 0.406 0.406 0.406 0.406 0.406 0.469 0.406 0.406 0.406 0.406 42.0 0.438 0.438 0.438 0.438 0.438 0.500 0.438 0.438 0.438 0.438 MAOP < 300 psi < 12.75 MAOP < 400 psi 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 14.0 0.188 0.188 0.188 0.188 0.188 0.203 0.188 0.188 0.188 0.188 16.0 0.188 0.188 0.188 0.188 0.188 0.281 0.188 0.188 0.188 0.188 18.0 0.219 0.188 0.188 0.188 0.188 0.281 0.219 0.188 0.188 0.188 20.0 0.250 0.219 0.219 0.219 0.219 0.312 0.250 0.219 0.219 0.219 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-14 AREMA Manual for Railway Engineering Pipelines Table 1-5-3. Minimum Nominal Wall Thickness (in.) for Uncased Carrier Pipe (Continued) D (in.) SMYS (psi) 35000 42000 52000 SMYS (psi) 60000 70000 35000 MAOP < 300 psi - Continued 42000 52000 60000 70000 MAOP < 400 psi - Continued 22.0 0.281 0.226 0.226 0.226 0.226 0.344 0.281 0.226 0.226 0.226 24.0 0.312 0.250 0.250 0.250 0.250 0.375 0.281 0.250 0.250 0.250 26.0 0.344 0.281 0.281 0.281 0.281 0.406 0.312 0.281 0.281 0.281 28.0 0.375 0.312 0.281 0.281 0.281 0.438 0.344 0.281 0.281 0.281 30.0 0.406 0.312 0.312 0.312 0.312 0.469 0.375 0.312 0.312 0.312 32.0 0.438 0.344 0.344 0.344 0.344 0.500 0.406 0.344 0.344 0.344 34.0 0.469 0.375 0.344 0.344 0.344 0.531 0.438 0.344 0.344 0.344 36.0 0.500 0.406 0.375 0.375 0.375 0.562 0.469 0.375 0.375 0.375 38.0 0.531 0.438 0.406 0.406 0.406 0.625 0.500 0.406 0.406 0.406 40.0 0.562 0.469 0.406 0.406 0.406 0.656 0.531 0.406 0.406 0.406 42.0 0.594 0.500 0.438 0.438 0.438 0.688 0.562 0.438 0.438 0.438 MAOP < 500 psi < 8.625 MAOP < 600 psi 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 10.75 0.188 0.188 0.188 0.188 0.188 0.203 0.188 0.188 0.188 0.188 12.75 0.219 0.188 0.188 0.188 0.188 0.250 0.203 0.188 0.188 0.188 14.0 0.250 0.188 0.188 0.188 0.188 0.281 0.210 0.188 0.188 0.188 16.0 0.281 0.219 0.188 0.188 0.188 0.312 0.250 0.188 0.188 0.188 18.0 0.312 0.250 0.188 0.188 0.188 0.344 0.281 0.219 0.188 0.188 20.0 0.344 0.281 0.219 0.219 0.219 0.375 0.312 0.250 0.219 0.219 22.0 0.375 0.312 0.250 0.226 0.226 0.438 0.344 0.281 0.226 0.226 24.0 0.406 0.344 0.281 0.250 0.250 0.469 0.375 0.312 0.250 0.250 26.0 0.469 0.375 0.281 0.281 0.281 0.500 0.406 0.344 0.281 0.281 28.0 0.500 0.406 0.312 0.281 0.281 0.562 0.469 0.375 0.312 0.312 30.0 0.531 0.438 0.344 0.312 0.312 0.594 0.500 0.406 0.344 0.312 32.0 0.562 0.469 0.375 0.344 0.344 0.625 0.531 0.406 0.375 0.344 34.0 0.625 0.500 0.406 0.344 0.344 0.688 0.562 0.438 0.375 0.344 36.0 0.656 0.531 0.438 0.375 0.375 0.719 0.594 0.469 0.406 0.375 38.0 0.688 0.562 0.469 0.406 0.406 0.750 0.625 0.500 0.438 0.406 40.0 0.719 0.594 0.500 0.406 0.406 0.781 0.688 0.531 0.469 0.438 42.0 0.750 0.656 0.500 0.438 0.438 0.844 0.719 0.562 0.500 0.469 MAOP < 700 psi MAOP < 800 psi < 6.625 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 8.625 0.188 0.188 0.188 0.188 0.188 0.203 0.188 0.188 0.188 0.188 0.219 0.188 0.188 0.188 0.188 0.250 0.203 0.188 0.188 0.188 10.75 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-15 1 3 4 Roadway and Ballast Table 1-5-3. Minimum Nominal Wall Thickness (in.) for Uncased Carrier Pipe (Continued) D (in.) SMYS (psi) 35000 42000 52000 SMYS (psi) 60000 70000 35000 MAOP < 700 psi - Continued 42000 52000 60000 70000 MAOP < 800 psi - Continued 12.75 0.281 0.219 0.188 0.188 0.188 0.312 0.250 0.188 0.188 0.188 14.0 0.312 0.250 0.188 0.188 0.188 0.344 0.281 0.219 0.188 0.188 16.0 0.344 0.281 0.219 0.188 0.188 0.375 0.312 0.250 0.219 0.188 18.0 0.375 0.312 0.250 0.219 0.219 0.438 0.344 0.281 0.226 0.219 20.0 0.438 0.344 0.281 0.226 0.226 0.469 0.406 0.312 0.250 0.250 22.0 0.469 0.406 0.312 0.281 0.226 0.500 0.438 0.344 0.281 0.250 24.0 0.500 0.438 0.344 0.281 0.250 0.562 0.469 0.375 0.312 0.281 26.0 0.562 0.469 0.375 0.312 0.281 0.625 0.500 0.406 0.344 0.312 28.0 0.594 0.500 0.406 0.344 0.281 0.656 0.562 0.438 0.375 0.312 30.0 0.656 0.531 0.438 0.375 0.312 0.719 0.594 0.469 0.406 0.344 32.0 0.688 0.562 0.469 0.406 0.344 0.750 0.625 0.500 0.438 0.375 34.0 0.750 0.625 0.500 0.438 0.375 0.812 0.688 0.531 0.469 0.406 36.0 0.781 0.656 0.531 0.469 0.375 0.844 0.719 0.562 0.500 0.438 38.0 0.844 0.688 0.562 0.500 0.406 0.906 0.750 0.625 0.531 0.438 40.0 0.875 0.750 0.594 0.500 0.438 0.938 0.812 0.656 0.562 0.469 42.0 0.938 0.781 0.625 0.531 0.469 1.000 0.844 0.688 0.594 0.500 MAOP < 900 psi MAOP < 1000 psi < 6.625 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 8.625 0.219 0.188 0.188 0.188 0.188 0.250 0.188 0.188 0.188 0.188 10.75 0.279 0.219 0.188 0.188 0.188 0.307 0.250 0.188 0.188 0.188 12.75 0.312 0.281 0.219 0.188 0.188 0.344 0.281 0.250 0.188 0.188 14.0 0.344 0.312 0.250 0.203 0.188 0.375 0.312 0.250 0.219 0.188 16.0 0.406 0.344 0.281 0.219 0.188 0.438 0.375 0.312 0.250 0.219 18.0 0.469 0.375 0.312 0.250 0.219 0.500 0.406 0.344 0.281 0.250 20.0 0.500 0.438 0.344 0.281 0.250 0.562 0.469 0.375 0.312 0.281 22.0 0.562 0.469 0.375 0.312 0.281 0.625 0.500 0.406 0.344 0.281 24.0 0.625 0.500 0.406 0.344 0.312 0.688 0.562 0.438 0.375 0.312 26.0 0.656 0.562 0.438 0.375 0.312 0.750 0.594 0.469 0.406 0.344 28.0 0.719 0.594 0.469 0.406 0.344 0.750 0.656 0.531 0.438 0.375 30.0 0.750 0.625 0.500 0.438 0.375 0.812 0.688 0.562 0.469 0.406 32.0 0.812 0.688 0.562 0.469 0.406 0.875 0.719 0.594 0.531 0.438 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-16 AREMA Manual for Railway Engineering Pipelines Table 1-5-3. Minimum Nominal Wall Thickness (in.) for Uncased Carrier Pipe (Continued) D (in.) SMYS (psi) 35000 42000 52000 SMYS (psi) 60000 70000 35000 MAOP < 900 psi - Continued 42000 52000 60000 70000 MAOP < 1000 psi - Continued 34.0 0.875 0.719 0.594 0.500 0.438 0.938 0.781 0.625 0.562 0.469 36.0 0.906 0.781 0.625 0.531 0.469 1.000 0.812 0.688 0.594 0.500 38.0 0.969 0.812 0.656 0.562 0.500 1.062 0.875 0.719 0.625 0.531 40.0 1.031 0.875 0.688 0.625 0.531 1.125 0.906 0.750 0.656 0.562 42.0 1.062 0.906 0.750 0.656 0.562 1.188 0.969 0.781 0.688 0.594 MAOP < 1100 psi MAOP < 1200 psi < 5.563 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 6.625 0.188 0.188 0.188 0.188 0.188 0.203 0.188 0.188 0.188 0.188 8.625 0.250 0.203 0.188 0.188 0.188 0.277 0.219 0.188 0.188 0.188 10.75 0.307 0.250 0.203 0.188 0.188 0.344 0.277 0.219 0.188 0.188 12.75 0.375 0.312 0.250 0.219 0.188 0.406 0.330 0.281 0.226 0.188 14.0 0.406 0.344 0.281 0.226 0.219 0.438 0.375 0.312 0.250 0.219 16.0 0.469 0.406 0.312 0.281 0.219 0.500 0.406 0.344 0.281 0.250 18.0 0.531 0.438 0.344 0.312 0.250 0.562 0.469 0.375 0.344 0.281 20.0 0.594 0.500 0.406 0.344 0.281 0.625 0.531 0.438 0.375 0.312 22.0 0.625 0.531 0.438 0.375 0.312 0.688 0.562 0.469 0.406 0.344 24.0 0.688 0.594 0.469 0.406 0.344 0.750 0.625 0.500 0.438 0.375 26.0 0.750 0.625 0.500 0.438 0.375 0.812 0.688 0.562 0.469 0.406 28.0 0.812 0.688 0.562 0.469 0.406 0.875 0.719 0.594 0.500 0.438 30.0 0.875 0.750 0.594 0.531 0.438 0.938 0.812 0.625 0.562 0.469 32.0 0.938 0.781 0.625 0.562 0.469 1.000 0.875 0.688 0.594 0.500 34.0 1.000 0.844 0.688 0.594 0.500 1.062 0.875 0.719 0.625 0.531 36.0 1.062 0.875 0.719 0.625 0.531 1.125 0.938 0.750 0.656 0.562 38.0 1.125 0.938 0.750 0.656 0.562 1.188 1.000 0.812 0.719 0.594 40.0 1.156 0.969 0.812 0.688 0.594 1.250 1.031 0.844 0.750 0.625 42.0 1.250 1.031 0.844 0.750 0.625 1.312 1.094 0.906 0.781 0.656 MAOP < 1300 psi MAOP < 1400 psi < 5.563 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 6.625 0.219 0.188 0.188 0.188 0.188 0.250 0.188 0.188 0.188 0.188 8.625 0.277 0.250 0.188 0.188 0.188 0.312 0.250 0.219 0.188 0.188 0.344 0.307 0.250 0.203 0.188 0.365 0.307 0.250 0.219 0.219 10.75 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-17 1 3 4 Roadway and Ballast Table 1-5-3. Minimum Nominal Wall Thickness (in.) for Uncased Carrier Pipe (Continued) D (in.) SMYS (psi) 35000 42000 52000 SMYS (psi) 60000 70000 35000 MAOP < 1300 psi - Continued 42000 52000 60000 70000 MAOP < 1400 psi - Continued 12.75 0.438 0.344 0.281 0.256 0.219 0.438 0.375 0.312 0.256 0.250 14.0 0.469 0.375 0.312 0.279 0.226 0.500 0.406 0.344 0.281 0.281 16.0 0.531 0.438 0.375 0.312 0.281 0.562 0.469 0.375 0.344 0.312 18.0 0.594 0.500 0.406 0.344 0.312 0.625 0.531 0.438 0.375 0.344 20.0 0.656 0.562 0.438 0.375 0.344 0.688 0.594 0.469 0.406 0.375 22.0 0.719 0.594 0.500 0.438 0.406 0.750 0.656 0.531 0.469 0.375 24.0 0.812 0.656 0.531 0.469 0.406 0.844 0.688 0.562 0.500 0.438 26.0 0.844 0.719 0.594 0.500 0.438 0.906 0.750 0.625 0.531 0.469 28.0 0.906 0.781 0.625 0.531 0.469 0.969 0.812 0.656 0.594 0.500 30.0 0.969 0.812 0.688 0.594 0.500 1.031 0.875 0.719 0.625 0.531 32.0 1.031 0.875 0.719 0.625 0.531 1.094 0.938 0.750 0.656 0.562 34.0 1.125 0.938 0.750 0.656 0.562 1.156 1.000 0.812 0.719 0.594 36.0 1.188 1.000 0.812 0.719 0.625 1.250 1.062 0.875 0.750 0.656 38.0 1.250 1.062 0.844 0.750 0.656 1.312 1.094 0.906 0.781 0.688 40.0 1.312 1.094 0.906 0.781 0.688 1.375 1.156 0.938 0.844 0.719 42.0 1.375 1.156 0.938 0.844 0.719 1.469 1.219 1.000 0.875 0.750 MAOP < 1500 psi < 4.5 MAOP < 1600 psi 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 5.563 0.219 0.188 0.188 0.188 0.188 0.219 0.188 0.188 0.188 0.188 6.625 0.250 0.203 0.188 0.188 0.188 0.280 0.219 0.188 0.188 0.188 8.625 0.312 0.277 0.219 0.188 0.188 0.344 0.277 0.250 0.219 0.188 10.75 0.406 0.344 0.279 0.226 0.219 0.438 0.344 0.279 0.250 0.219 12.75 0.469 0.406 0.312 0.281 0.250 0.500 0.406 0.344 0.312 0.250 14.0 0.500 0.438 0.344 0.312 0.250 0.562 0.469 0.375 0.312 0.281 16.0 0.594 0.500 0.406 0.344 0.312 0.625 0.531 0.438 0.375 0.312 18.0 0.656 0.562 0.469 0.406 0.344 0.688 0.594 0.469 0.406 0.344 20.0 0.719 0.625 0.494 0.438 0.375 0.781 0.656 0.531 0.469 0.406 22.0 0.812 0.688 0.562 0.469 0.406 0.844 0.719 0.594 0.500 0.438 24.0 0.875 0.750 0.594 0.531 0.438 0.938 0.781 0.625 0.562 0.469 26.0 0.938 0.812 0.656 0.562 0.500 1.000 0.844 0.688 0.594 0.500 28.0 1.031 0.875 0.688 0.625 0.531 1.062 0.906 0.750 0.656 0.562 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-18 AREMA Manual for Railway Engineering Pipelines Table 1-5-3. Minimum Nominal Wall Thickness (in.) for Uncased Carrier Pipe (Continued) D (in.) SMYS (psi) 35000 42000 52000 SMYS (psi) 60000 70000 35000 MAOP < 1500 psi - Continued 42000 52000 60000 70000 MAOP < 1600 psi - Continued 30.0 1.094 0.938 0.750 0.656 0.562 1.156 0.969 0.781 0.688 0.594 32.0 1.156 0.969 0.812 0.688 0.594 1.219 1.031 0.844 0.719 0.625 34.0 1.250 1.031 0.844 0.750 0.625 1.312 1.094 0.906 0.781 0.656 36.0 1.312 1.094 0.906 0.781 0.688 1.375 1.156 0.938 0.812 0.719 38.0 1.375 1.156 0.938 0.844 0.719 1.469 1.219 1.000 0.875 0.750 40.0 1.438 1.219 1.000 0.875 0.750 1.531 1.281 1.062 0.906 0.781 42.0 1.531 1.281 1.062 0.938 0.781 — 1.344 1.094 0.969 0.844 MAOP < 1700 psi MAOP < 1800 psi < 4.0 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 4.5 0.188 0.188 0.188 0.188 0.188 0.203 0.188 0.188 0.188 0.188 5.563 0.258 0.188 0.188 0.188 0.188 0.258 0.219 0.188 0.188 0.188 6.625 0.280 0.250 0.188 0.188 0.188 0.312 0.250 0.219 0.188 0.188 8.625 0.375 0.312 0.250 0.219 0.188 0.375 0.312 0.250 0.219 0.188 10.75 0.438 0.365 0.312 0.256 0.219 0.469 0.406 0.312 0.279 0.250 12.75 0.531 0.438 0.375 0.312 0.281 0.562 0.469 0.375 0.344 0.281 14.0 0.594 0.500 0.406 0.344 0.312 0.625 0.500 0.406 0.375 0.312 16.0 0.656 0.562 0.438 0.406 0.344 0.688 0.594 0.469 0.406 0.344 18.0 0.750 0.625 0.500 0.438 0.375 0.781 0.656 0.531 0.469 0.406 20.0 0.812 0.688 0.562 0.500 0.406 0.875 0.719 0.594 0.500 0.438 22.0 0.906 0.750 0.625 0.531 0.469 0.969 0.781 0.656 0.562 0.500 24.0 1.000 0.812 0.656 0.594 0.500 1.031 0.875 0.719 0.625 0.531 26.0 1.062 0.906 0.719 0.625 0.531 1.125 0.938 0.750 0.656 0.562 28.0 1.156 0.969 0.781 0.688 0.594 1.219 1.000 0.812 0.719 0.625 30.0 1.219 1.031 0.844 0.719 0.625 1.312 1.094 0.875 0.750 0.656 32.0 1.312 1.094 0.875 0.781 0.656 1.375 1.156 0.938 0.812 0.688 34.0 1.375 1.156 0.938 0.812 0.688 1.500 1.219 1.000 0.875 0.750 36.0 1.469 1.219 1.000 0.875 0.750 1.562 1.312 1.062 0.906 0.781 38.0 1.562 1.312 1.062 0.906 0.781 — 1.375 1.125 0.969 0.844 40.0 — 1.375 1.094 0.969 0.844 — 1.438 1.156 1.000 0.875 42.0 — 1.438 1.156 1.000 0.875 — 1.500 1.219 1.062 0.906 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-19 1 3 4 Roadway and Ballast Table 1-5-3. Minimum Nominal Wall Thickness (in.) for Uncased Carrier Pipe (Continued) D (in.) SMYS (psi) 35000 42000 52000 SMYS (psi) 60000 70000 35000 MAOP < 1900 psi 42000 52000 60000 70000 MAOP < 2000 psi < 3.5 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 0.188 4.0 0.188 0.188 0.188 0.188 0.188 0.219 0.188 0.188 0.188 0.188 4.5 0.219 0.188 0.188 0.188 0.188 0.219 0.188 0.188 0.188 0.188 5.563 0.258 0.219 0.188 0.188 0.188 0.281 0.250 0.188 0.188 0.188 6.625 0.312 0.250 0.219 0.188 0.188 0.344 0.280 0.219 0.188 0.188 8.625 0.406 0.344 0.281 0.277 0.219 0.438 0.344 0.281 0.250 0.219 10.75 0.500 0.406 0.344 0.312 0.250 0.531 0.438 0.375 0.312 0.256 12.75 0.594 0.500 0.406 0.344 0.312 0.625 0.531 0.438 0.375 0.312 14.0 0.656 0.531 0.438 0.375 0.344 0.688 0.562 0.469 0.406 0.344 16.0 0.750 0.625 0.500 0.438 0.375 0.781 0.656 0.531 0.469 0.406 18.0 0.812 0.688 0.562 0.500 0.438 0.875 0.719 0.594 0.500 0.438 20.0 0.906 0.781 0.625 0.531 0.469 0.969 0.812 0.656 0.562 0.500 22.0 1.000 0.844 0.688 0.594 0.500 1.062 0.875 0.719 0.625 0.531 24.0 1.094 0.906 0.750 0.656 0.562 1.156 0.969 0.781 0.688 0.594 26.0 1.188 1.000 0.812 0.688 0.594 1.250 1.062 0.844 0.750 0.625 28.0 1.312 1.062 0.875 0.750 0.656 1.344 1.125 0.906 0.781 0.688 30.0 1.375 1.156 0.938 0.812 0.688 1.438 1.219 0.969 0.844 0.719 32.0 1.469 1.219 1.000 0.844 0.750 1.531 1.281 1.031 0.906 0.781 34.0 1.562 1.312 1.062 0.906 0.781 — 1.375 1.094 0.969 0.812 36.0 — 1.375 1.125 0.969 0.844 — 1.438 1.156 1.000 0.875 38.0 — 1.438 1.188 1.031 0.875 — 1.531 1.219 1.062 0.906 40.0 — 1.531 1.219 1.062 0.906 — — 1.312 1.125 0.969 42.0 — — 1.281 1.125 0.969 — — 1.375 1.188 1.000 5.2.3.1 Allowable Hoop Stress Due to Internal Pressure The maximum allowable hoop stress due to internal pressure shall be sixty percent of SMYS or per ANSI Code if lower allowable percentage of hoop stress applies. 5.2.3.2 Length of Special Carrier Pipe Carrier pipe, with nominal wall thickness greater than or equal to those shown in Table 1-5-3, shall extend from right-of-way line to right-of-way line, or 25 ft. from centerline track, whichever distance is greater, unless special conditions exist which prevent this from occurring or as approved by the engineer. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-20 AREMA Manual for Railway Engineering Pipelines 5.2.3.3 Cathodic Protection a. Carrier pipes must be coated and cathodically protected to industry standards and test sites for monitoring pipeline provided within 50 ft. of crossing. b. Where carrier pipe is cathodically protected, the engineer shall be notified and a suitable test made to ensure that other railway structures and facilities are adequately protected from the cathodic current in accordance with the recommendation of current Reports of Correlating Committee on Cathodic Protection, published by the National Association of Corrosion Engineers. 5.2.4 CONSTRUCTION (1993) 5.2.4.1 Special Protection When the engineer determines there is a possibility of having foreign materials in the subgrade, unusual potential for third party damage exists, or for other reasons, special protection of the carrier pipe will be required. Special protection may require concrete jacketed steel pipe be used, or protection slabs be placed above the pipe, the depth of burial increased, or other means. Soil borings may also be required to determine soil characteristics and to identify if foreign material is present in the bore. 5.2.4.2 Depth of Burial a. b. Carrier line pipe under railway tracks shall not be less than 10 ft. from the base of railway rail to the top of the pipe at its closest point. At all other locations on the rights-of-way the minimum ground cover must be 6 ft. Where it is not possible to secure the above depths, casings as specified in Section 5.1, Specifications for Pipelines Conveying Flammable Substances, or other means of protection, will be required. 1 The Inspection and Testing, and Shutoff Valves specifications are the same as in Section 5.1, Specifications for Pipelines Conveying Flammable Substances, Article 5.1.6.3 and Article 5.1.6.6 respectively. 5.2.4.3 Longitudinal Pipelines Longitudinal pipelines should be located as far as possible from any track. They must not be within 25 ft. from the centerline of any track and must have a minimum of 6 ft. ground cover over the pipeline up to 50 ft. from centerline of track. Where pipeline is laid more than 50 ft. from centerline of track, minimum cover shall be at least 5 ft. Pipelines must be marked by a sign approved by the engineer every 500 ft. and at every road crossing, streambed, other utility crossing, and at locations of major change in direction of the line. The nominal wall thickness of the pipeline is to be in accordance with Table 1-5-3. 5.2.4.4 Method of Installation Installations shall be bored or jacked, and shall have a bored hole diameter essentially the same as the outside diameter of the pipe plus the thickness of the protective coating. If voids should develop or if the bored hole diameter is greater than the outside diameter of the pipe (including coating) by more than approximately 1 in., remedial measures as approved by the engineer shall be taken. Boring operations shall not be stopped if such stoppage would be detrimental to the railway. 5.2.5 APPROVAL OF PLANS (2002) a. Plans for proposed installation shall be submitted to and meet the approval of the engineer before construction is begun. b. Plans shall be drawn to scale showing the relation of the proposed pipeline to railway tracks, angle of crossing, location of valves, railway survey station, right-of-way lines and general layout of tracks and railway facilities. Plans should also show a cross section (or sections) from field survey, showing pipe in © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-21 3 4 Roadway and Ballast relation to actual profile of ground and tracks. If open-cutting or tunneling is necessary, details of sheeting and method of supporting tracks or driving tunnel shall be shown. c. In addition to the above, plans should contain the following data found in Table 1-5-4. Table 1-5-4. Plan Data Description Carrier Pipe Contents to be handled Outside Diameter Pipe Material Specification and grade Wall thickness Actual Working pressure Type of joint Coating Method of installation Bury: Base of rail to top of carrier ft. Bury: (Not beneath tracks) Bury: (Roadway ditches) ft. Bury: Base of rail to bottom jacking/receiving pits Yes in. ft. Distance C.L. track to face of jacking/receiving pits Cathodic protection? in. ft. ft. in. in. No 5.2.6 EXECUTION OF WORK (1993) The execution of work on railway rights-of-way, including the supporting of tracks, shall be subject to the inspection and direction of the engineer. 5.2.7 COMMENTARY (1993) A commentary on the “Design of Uncased Pipelines at Railroad Crossings” and the “Guidelines for Pipelines Crossing Railroads” outline the design methodology as developed by Cornell University under the sponsorship of the Gas Research Institute. This information is published in AREA Bulletin No. 738 Vol. 93, 1992. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-22 AREMA Manual for Railway Engineering Pipelines SECTION 5.3 SPECIFICATIONS FOR PIPELINES CONVEYING NON-FLAMMABLE SUBSTANCES 5.3.1 SCOPE (1993) Pipelines included under these specifications are those installed to carry steam, water or any nonflammable substance except nonflammable gas products as covered in Section 5.2 which, from its nature or pressure, might cause damage if escaping on or in the vicinity of railway property. The term “engineer” as used herein means chief engineer of the railway company, or the authorized representative. 5.3.2 GENERAL REQUIREMENTS (2002) a. Pipelines under railway tracks and across railway rights-of-way shall be encased in a larger pipe or conduit called the casing pipe as indicated in Figure 1-5-3. Casing pipe may be omitted under the following conditions: (1) Under secondary or industry tracks as approved by the engineer. (2) On pipelines in streets where joints are of leakproof construction and the pipe material will safely withstand the combination of internal pressure and external loads. (3) For non-pressure sewer crossings where the pipe strength is capable of withstanding railway loading. 1 b. Pipelines shall be installed under tracks by boring or jacking, if practicable. c. Pipelines shall be located, where practicable, to cross tracks at approximately right angles thereto but preferably at not less than 45 degrees and shall not be placed within culverts nor under railway bridges where there is likelihood of restricting the area required for the purposes for which the bridges or culverts were built, or of endangering the foundations. d. Pipelines laid longitudinally on railway rights-of-way shall be located as far as practical from any tracks or other important structures . If located within 25 ft. of the centerline of any track or where there is danger of damage from leakage to any bridge, building or other important structure, the carrier pipe shall be encased or of special design as approved by the engineer. 3 4 Note 1: See Article 5.3.4.3 Note 2: See Article 5.3.5.2 Figure 1-5-3. Casing Pipe Installation e. Where laws or orders of public authority prescribe a higher degree of protection than specified herein, then the higher degree of protection so prescribed shall supersede the applicable portions. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-23 Roadway and Ballast f. Pipelines and casing pipe shall be suitably insulated from underground conduits carrying electric wires on railway rights-of-way. Pipeline must be able to be electronically located. 5.3.2.1 Pipeline Inspection and Maintenance a. Pipeline owners engaged in the transport of non-flammable substances are subject to regulations of the Federal Government. These regulations require certain inspection routines that, in the general case, are conducted from within the carrier pipe or by non-destructive methods not requiring it be exposed. b. It is the responsibility of the pipeline owner to conduct the necessary inspections without interference to the operations of the Railway Company. Should it become necessary to expose a pipe for an inspection, or for its replacement, the owner shall design a procedure that does not interfere with Railway operations, and shall make prior arrangements with the Railway as may be necessary to permit safe conduct of the work. c. Pipeline maintenance shall be limited to the installation of a new carrier pipe in an existing casing, renewal of carrier and casing pipe separators or the installation of a new crossing. In all cases, the work shall be conducted in the same manner as in the installation of a new crossing, which is subject to the requirements of these specifications. Casings abandoned or replaced by new location work shall be backfilled by methods and materials as directed by the Engineer. The location of abandoned facilities shall be recorded and records maintained by the pipeline owner. d. The owners of pipelines not subject to regulation requiring inspection are expected to inspect their facilities as a matter of due diligence in the conduct of its business. The Railway may, as a right but not a duty, require an inspection of the construction, to include receiving a written report of findings certified by a registered professional engineer. Maintenance of these facilities shall be conducted as above described. 5.3.3 CARRIER PIPE (2002) a. Carrier line pipe and joints shall be of acceptable material and construction as approved by the engineer. Joints for carrier line pipe operating under pressure shall be leakproof mechanical or welded type. b. The pipe shall be laid with sufficient slack so that it is not in tension. c. Plastic carrier pipe materials includes thermoplastic and thermoset plastic pipes. Thermoplastic types include Polyvinyl Chloride (PVC), Acrylonitrile Butadiene Styrene (ABS), Polyethylene (PE), Polybutylene (PB), Cellulose Acetate Butyrate (CAB) and Styrene Rubber (SR). Thermoset types include Reinforced Plastic Mortar (RPM), Reinforced Thermosetting Resin (FRP) and Fiberglass Reinforced Plastic (FRP). (1) Plastic pipe material shall be resistant to the chemicals with which contact can be anticipated. Plastic carrier pipe shall not be utilized where there is potential for contact with petroleum contaminated soils or other non-polar organic compounds that may be present in surrounding soils. (2) Plastic carrier pipes operating under pressure shall be encased according to Article 5.3.4. Casing may be omitted with approval by the engineer, provided that minimum burial depth is increased to comply with the most conservative requirements of either: the engineer's instructions, current ANSI specifications, current OSHA regulations, or local regulatory agency specifications. (3) Plastic carrier pipes without casing shall be designed to withstand internal operating pressures according to ANSI B31.3 specifications. External loads due to soil pressures and railroad live loads from Table 4.9.1 of Chapter 1 shall be used to determine deflection. Deflection resulting from external loading shall be calculated assuming there is no internal pressure. Deflection shall be limited to no more than 5% of the diameter. (4) Design shall consider differential settlement of attachments, longitudinal bending, shear loadings due to uneven settlement of pipe bedding, temperature induced stresses, ground movement due to seasonal variations in moisture content (i.e. expansive clays), seismic ground movement and potential for ground cover surface erosion. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-24 AREMA Manual for Railway Engineering Pipelines (5) The plastic pipe material must be compatible with the type of product conveyed and the temperature range anticipated for the transported materials and surrounding environment. The maximum allowable operating pressure is 100 psi. Plastic carrier pipe design and installation shall conform to the ANSI B31.3 specifications and/or the following specifications: d. Specification No. Carrier pipe properties: ANSI/AWWA C900-89 Polyvinyl Chloride (PVC) pressure pipe, 4 in. through 12 in. for water distribution. ANSI/AWWA C901-96 Polyethylene (PE) pressure pipe and tubing, 1/2 in. through 3 in. for water service. ANSI/AWWA C902-88 Polybutylene (PB) pressure pipe and tubing, 1/2 in. through 3 in. for water. ANSI/AWWA C905-88 Polyvinyl Chloride (PVC) water transmission pipe, nominal diameters 14 in. through 36 in. ANSI/AWWA C906-90 Polyethylene (PE) pressure pipe and fittings, 4 in. through 63 in. for water distribution. ANSI/AWWA C907-90 Polyvinyl Chloride (PVC) pressure fittings for water, 4 in. through 8 in. ANSI/AWWA C950-95 Fiberglass pressure pipe. Codes, specifications and regulations current at time of constructing the pipeline shall govern the installation of the facility within the railway rights-of-way. The proof testing of the strength of carrier pipe shall be in accordance with ANSI requirements. 1 5.3.4 STEEL CASING PIPE (2002) a. b. Casing pipe and joints shall be leakproof construction, capable of withstanding railroad loading. The inside diameter of the casing pipe shall be at least 2 in. greater than the largest outside diameter of the carrier pipe, joints or couplings, for carrier pipe less than 6 in. in diameter; and at least 4 in. greater for carrier pipe 6 in. and over in diameter. It shall, in all cases, be great enough to allow the carrier pipe to be removed subsequently without disturbing the casing pipe or roadbed. 3 When casing is installed without benefit of a protective coating or said casing is not cathodically protected, the wall thickness shown above shall be increased to the nearest standard size which is a minimum of 0.063 in. greater than the thickness required except for diameters under 12-3/4 in. (Table 1-5-5). 4 5.3.4.1 Steel Casing Pipe Strength Steel casing pipe shall have a specified minimum yield strength, SMYS, of at least 35,000 psi. 5.3.4.2 Concrete and Corrugated Metal Pipe For pressures under 100 psi in the carrier pipe, the casing pipe may be reinforced concrete pipe conforming to AREMA specifications in Chapter 8, Concrete Structures and Foundations, Part 10, Reinforced Concrete Culvert Pipe, coated corrugated metal pipe or steel tunnel liner plate conforming to the AREMA specifications for such pipe, Part 4, Culverts, this Chapter. 5.3.4.3 Length of Pipe Casing pipe under tracks and across railway rights-of-way shall extend to the greater of the following distances, measured at right angles to centerline of track. If additional tracks are constructed in the future or the railway determines that the roadbed should be widened, the casing shall be extended or other special design incorporated. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-25 Roadway and Ballast • 2 ft. beyond toe of slope. • 3 ft. beyond ditch. • A minimum distance of 25 ft. from center of outside track when end of casing is below ground. Table 1-5-5. Minimum Wall Thickness for Steel Casing Pipe for E80 Loading Nominal Diameter (inches) When coated or When not coated or cathodically protected cathodically protected Nominal Thickness (inches) Nominal Thickness (inches) 12-3/4 and under 0.188 0.188 14 0.188 0.250 16 0.219 0.281 18 0.250 0.312 20 and 22 0.281 0.344 24 0.312 0.375 26 0.344 0.406 28 0.375 0.438 30 0.406 0.469 32 0.438 0.500 34 and 36 0.469 0.531 38 0.500 0.562 40 0.531 0.594 42 0.562 0.625 44 and 46 0.594 0.656 48 0.625 0.688 50 0.656 0.719 52 0.688 0.750 54 0.719 0.781 56 and 58 0.750 0.812 60 0.781 0.844 62 0.812 0.875 64 0.844 0.906 66 and 68 0.875 0.938 70 0.906 0.969 72 0.938 1.000 5.3.5 CONSTRUCTION (2002) Casing pipe shall be so constructed as to prevent leakage of any substance from the casing throughout its length except at ends. Casing shall be so installed as to prevent the formation of a waterway under the railway, with an even bearing throughout its length, and shall slope to one end (except for longitudinal occupancy). © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-26 AREMA Manual for Railway Engineering Pipelines Where casing and/or carrier pipe is cathodically protected, the engineer shall be notified and suitable test made to ensure that other railway structures and facilities are adequately protected from the cathodic current in accordance with the recommendations of current Reports of Correlating Committee on Cathodic Protection, published by the National Association of Corrosion Engineers. 5.3.5.1 Method of Installation a. Installations by open-trench methods shall comply with Part 4, Culverts, Section 4.12, Assembly and Installation of Pipe Culverts. Plastic pipelines shall be installed according to ASTM D 2774 and D 2321. b. Bored or jacked installations shall have a bored hole diameter essentially the same as the outside diameter of the pipe plus the thickness of the protective coating. If voids should develop or if the bored hole diameter is greater than the outside diameter of the pipe (including coating) by more than approximately 1 in., remedial measures as approved by the chief engineer of the railway company shall be taken. Boring operations shall not be stopped if such stoppage would be detrimental to the railway. c. Tunneling operations shall be conducted as approved by the engineer. If voids are caused by the tunneling operations, they shall be filled by pressure grouting or by other approved methods which will provide proper support. 5.3.5.2 Depth of Installation 5.3.5.2.1 Casing Pipe Casing pipe under railway tracks and across railway rights-of-way shall be not less than 5-1/2 ft. from base of railway rail to top of casing at its closest point, except that under secondary or industry tracks this distance may be 4-1/2 ft. On other portions of rights-of-way where casing is not directly beneath any track, the depth from ground surface or from bottom of ditches to top of casing shall not be less than 3 ft. 1 5.3.5.2.2 Carrier Pipe Carrier pipe installed under secondary or industry tracks without benefit of casing shall be not less than 4-1/2 ft. from base of railway rail to top of pipe at its closest point nor less than 3 ft. from ground surface or from bottom of ditches. Plastic carrier pipe must be encased under secondary or industry tracks according to Article 5.3.4. 3 5.3.5.3 Shut-Off Valves Accessible emergency shut-off valves shall be installed within effective distances each side of the railway as mutually agreed to by the engineer and the pipeline company. These valves should be marked with signs for identification. Where pipelines are provided with automatic control stations at locations and within distances approved by the engineer, no additional valves shall be required. 5.3.5.4 Longitudinal Pipelines Pipeline laid longitudinally on railway rights-of-way 50 ft. or less from centerline of track, shall be buried not less than 4 feet from ground surface to top of pipe. Where pipeline is laid more than 50 ft. from centerline of track, minimum cover shall be at least 3 feet. Plastic carrier pipe may be utilized for longitudinal installations with approval by the engineer, but shall be encased within the right of way. Casing may be omitted with approval of the engineer, provided that minimum bury depth is increased to comply with the most conservative requirements of either: the engineer’s instructions, current ANSI specifications, current OSHA regulations, or local regulatory agency regulations. Pipelines must be marked by a sign approved by the engineer every 500 ft. and at every road crossing, streambed, other utility crossing, and at locations of major change in direction of the line. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-27 4 Roadway and Ballast 5.3.6 APPROVAL OF PLANS (1993) Plans for proposed installation shall be submitted to and meet the approval of the engineer before construction is begun. Plans shall be drawn to scale showing the relation of the proposed pipeline to railway tracks, angle of crossing, location of valves, railway survey station, right-of-way lines and general layout of tracks and railway facilities. Plans should also show a cross section (or sections) from field survey, showing pipe in relation to actual profile of ground and tracks. If open-cutting or tunneling is necessary, details of sheeting and method of supporting tracks or driving tunnel shall be shown. a. In addition to the above, plans should contain the following data: Table 1-5-6. Plan Data Carrier Pipe Casing Pipe Contents to be handled Outside Diameter Pipe Material Specification and grade Wall thickness Actual Working pressure Type of joint Coating Method of installation Seals: Both ends: One end: Type: Bury: Base of rail to top of casing Bury: (Not beneath tracks) ft. in. ft. Bury: (Roadway ditches) ft. in. in. Type, size and spacing of insulators or supports Distance C.L. track to face of jacking/receiving pits Bury: Base of rail to bottom jacking/receiving pits Cathodic protection? Yes No ft. ft. in. in. 5.3.7 EXECUTION OF WORK (1993) The execution of the work on railway rights-of-way, including the supporting of tracks, shall be subject to the inspection and direction of the engineer. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-28 AREMA Manual for Railway Engineering Pipelines SECTION 5.4 SPECIFICATIONS FOR OVERHEAD PIPELINES CROSSINGS 5.4.1 SCOPE This section shall govern the design of pipelines which cross the tracks or right-of-way of a Railway Company on overhead structures. It shall include pipelines attached to existing or new vehicle or pedestrian bridges, and existing or new bridges designed for the exclusive use of pipeline facilities. It shall apply to pipelines designed for all levels of operating pressures, to include vacuums, and to all commodities, flammable and non-flammable, usually transported through pipelines. 5.4.2 GENERAL CONDITIONS 5.4.2.1 Location Investigation Where possible, pipelines shall be installed underground. There may be circumstances that warrant consideration of an overhead pipeline crossing; however, an overhead crossing of the tracks or right-of-way of a Railway by a pipeline facility will be investigated for permitting only in the case where the applicant can demonstrate it has exercised due diligence in locating a subgrade crossing. 5.4.2.2 Use of Existing Structures In no case shall a bridge or overhead structure owned or maintained by a Railway be used for the attachment of a pipeline facility. Applications proposing to make an attachment to an overhead structure owned and maintained by a party other than a Railway shall submit evidence that the owner of the structure has reviewed the plan and has issued, or proposes to issue, a permit or license for the facility. 1 5.4.3 GENERAL DESIGN REQUIREMENTS 5.4.3.1 Leak Protection The design shall provide for protection of the property and track structure of a Railway in the event of a pipeline leak or failure by use of a casing pipe or other means acceptable to the Railway. The design shall direct leaking liquid and dense gaseous products off the Railway right of way, but in no case, less than 25 feet beyond the back of parallel roadway ditches. 3 5.4.3.2 Emergency Shut-Off Valves Accessible emergency shut-off valves shall be installed within an effective distance on each side of the Railway right of way. The Engineer may, at his option, accept existing automatic control stations as suitable emergency shut-off valves. 5.4.3.3 Other Emergency telephone numbers shall be clearly posted on both ends of an overhead pipeline crossing, and pipelines and pipeline bridge structures must have effective apparatus to prevent unauthorized access. Additional pipeline attachments to an existing overhead pipeline crossing shall be approved by the Railway. Overhead pipelines could be subjected to high temperatures from the exhaust stacks of stationary running locomotives positioned directly under the carrier pipe. Pipeline contents and the pipeline materials may be adversely affected. The design shall incorporate suitable insulation or other heat deflection measures to prevent damages and insure pipeline integrity under high temperature conditions. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-29 4 Roadway and Ballast 5.4.4 STRUCTURAL ELEMENTS The structural elements of an overhead pipeline facility shall be the casing pipe, the carrier pipes, attaching hangers or bearings and the supporting bridge. 5.4.4.1 Pipeline Design 5.4.4.1.1 Casing Pipes Casing pipes shall be assumed to provide no structural support to the carrier pipe. The dead load of the casing pipe shall be included in the calculation of the dead load of the carrier pipe, and the load effects of wind and ice on the carrier pipe shall be calculated with respect to the diameter of the casing pipe. 5.4.4.1.2 Carrier Pipes Carrier pipes shall be designed in accordance with the most restrictive applicable federal or local regulation for the operating pressure and commodity of the facility. In addition to the loads exerted on the pipe by the conditions of its operation, the structural loads resulting from suspension or bearing conditions shall be considered. 5.4.4.2 Supporting Bridge Design 5.4.4.2.1 General Design Considerations Bridge spans, bents or piers and foundations shall be designed in accordance with generally accepted engineering practice, accounting for all dead, live, impact, seismic and secondary force loads. Pipe hanger and bearing attachment device design shall consider thermal expansion and seismic displacements. Drawings, plans, calculations and other documents representing the details of an application shall be prepared, signed and sealed by a professional engineer registered to practice in the state of the installation. 5.4.4.2.2 New Overhead Pipeline Bridges Overhead pipeline bridges shall be designed in accordance with the following criteria: Clearances shall be: VERTICAL—Not less than 25 feet above highest top of rail of the tracks to be spanned, except that cable supported spans shall have a vertical clearances of not less than 50 feet. HORIZONTAL—Not less than 25 feet from the centerline of the nearest existing main, siding, spur, or industry track, except in cases where the Engineer directs that additional clearance for future tracks must be provided. If conditions warrant, the engineer may require Pier Protection in accordance with Chapter 8, Concrete Structures and Foundations, Part 2, Reinforced Concrete Design. New beam span, girder and truss type structures and the details of the proposed attachment shall be designed in general accordance with Chapter 15 of this Manual of Recommended Practice. New cable suspended type structures shall be reviewed only upon special application to the Railway. Such application shall identify the design specifications to be used, to include the loads, allowable stresses and design considerations to be applied. Unless otherwise directed by the Engineer, cable supported spans shall include a minimum floor system with lateral bracing. 5.4.4.2.3 Attachments to Existing Overhead Bridges Where the pipeline is to be attached to an existing overhead structure not specifically designed for pipelines, the following shall apply: © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-30 AREMA Manual for Railway Engineering Pipelines Existing structures proposed as support for a pipeline shall be investigated for the additional loads of the operating pipeline facility. Additionally, the report of the professional engineer shall contain a conclusion with respect to the effects of the additional loads on the existing structure. Pipelines shall be installed inside the main structural members of the supporting bridge. In cases where this is not practical, the pipeline may be attached to the outside surface of the structure, but in no case shall the bottom of the pipeline be less than one foot above the elevation of the lowest main structural member of the supporting bridge. Pipe hanger and bearing attachment device design, and their connections to the supporting structure and the pipeline, shall be based on unit stresses equal to one-half (1/2) those otherwise permitted. Attachment device design shall consider thermal expansion, live loads deflection of the existing bridge, and seismic displacements. Pipeline and attachment designs shall consider the force and effect of the elements of the weather. Attachments shall be protected against corrosion in situations where chemical ice removal is utilized, or other corrosive condition is known or suspected. 5.4.5 INSPECTION AND MAINTENANCE Overhead pipelines, attachment devices, and supporting structures should be inspected and maintained on a routine basis. Also, emergency response procedures should be developed to handle a situation in which an accident or incident might jeopardize the integrity of pipeline facility. SECTION 5.5 SPECIFICATIONS FOR FIBER OPTIC “ROUTE” CONSTRUCTION ON RAILROAD RIGHT OF WAY 1 5.5.1 SCOPE (2001) These general requirements and specifications are provided only as a guideline for the successful completion of fiber optic installation. This shall include parallel and crossings on railroad right-of-way by railroads or outside communication companies that enter into agreements with railroads. All railroads shall reserve the right to change these recommendations as needed, and are not to be taken as authority to construct without prior review and approval by each of the participating railroads. Any items not covered specifically herein are to be in accordance with American Railway Engineering and Maintenance-of-Way Association (AREMA) standards and recommended practices, subject to the approval of the participating railroad’s Engineering Department. All railroads shall reserve the right to change these recommendations as needed without prior notice. A glossary of terms used in this document follows in Article 5.5.7. Dimensions are given in English with metric units in parentheses. 5.5.2 PLANNING (2001) 5.5.2.1 Coordinate the engineering criteria, from the preliminary route inspection through the actual route design, with railroad representative. 5.5.2.2 When planning a fiber system project. a. Identify and note on maps any potential impact to the railroad track structure or right-of-way. b. Note vegetation, property uses and topography not indicated on maps. c. Note cuts and fills. d. Identify potential track crossings, particularly under-track bores. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-31 3 4 Roadway and Ballast 5.5.2.3 Fiber Optic installations are governed by unique rules and regulations. It is the responsibility of the Fiber Optic Company that these be adhered to during planning, including preliminary investigations and route surveys on the railroad’s right-of-way. 5.5.2.4 Special permission is required for the use of all vehicles, including ATV’s, on the railroad’s right-ofway. Obtain permission to occupy the property or right-of-way of landowners other than the railroad. 5.5.2.5 It is the fiber optic company’s responsibility to obtain any permits, if required. 5.5.3 DESIGN (2001) 5.5.3.1 Conventional Build General Requirements (See Paragraph 5.5.3.6 for Railplow) 5.5.3.1.1 Detail all fiber facilities including lines, repeater sites, junctions, and structures. 5.5.3.1.2 Design the fiber system, if practical, to run near the outer limits of the Railroad’s right-of-way. Keep the fiber system running line as straight as possible while maintaining a consistent distance from track centerline. 5.5.3.1.3 Design the fiber system to run on the field side of all railroad structures, including bridges, signal facilities, buildings and platforms. 5.5.3.1.4 If the fiber system has to be placed under an existing signal or communication structure, place the system a minimum of 10 feet (3.05 meters) under natural ground. This extra depth may also be required in “signal sensitive areas” such as interlocking or control plants. 5.5.3.1.5 If the fiber system has to be located under existing signal or communication wires, a minimum 2 feet (.61 meters) of separation is required. 5.5.3.1.6 Fiber optic cable must not be installed within 5 feet (1.52 meters) of underground power or signal lines, unless suitably insulated. 5.5.3.1.7 If the fiber system is designed within 30 feet (9.14 meters) of a track centerline or structure of any type, excavations within this area may require shoring designed to include train or structure surcharges. In such cases, submit shoring plans with calculations, stamped by a licensed civil engineer, to the railroad for approval prior to construction. See 5.5.3.2 Trenches and Excavations. Refer to Figure 1-5-11. 5.5.3.1.8 Do not design fiber system components that create stumbling hazards on the railroad’s right-ofway. 5.5.3.1.9 Design the fiber system to be installed a minimum of 42 inches (1.07 meters) below natural ground, except as noted herein. See Figure 1-5-6. 5.5.3.1.10 In the event local ground conditions prohibit the placement of the fiber system at a depth of at least 42 inches (1.07 meters), the fiber system must be encased, and specific approval by the railroad is required. 5.5.3.1.11 Compact all backfill in excavations and trenches to 95% maximum density as defined in ASTM Standard D698. Use clean, suitable backfill material. 5.5.3.1.12 Design the fiber system to be buried a minimum of 60 inches (1.52 meters) below the bottom of all culverts on the railroad’s right-of-way, or around the end of the culvert (field side) and 60 inches (1.52 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-32 AREMA Manual for Railway Engineering Pipelines meters) below the bottom of the flow line. Only after specific evaluation by the railroad will any system be allowed to be placed over the top of any culvert. See Figure 1-5-6. 5.5.3.1.13 Locate and identify buried utilities and other potential obstructions. 5.5.3.1.14 Do not attach the fiber system to railroad bridges to cross waterways, highways, etc., unless no other feasible alternative exists. Fully explore the burying alternative before submitting requests to attach the fiber system to a bridge, and provide appropriate documentation, detailing the reasons why an attachment is necessary. a. Submit bridge attachment designs, for approval prior to construction. Include details at and around the bridge backwalls. b. Design bridge attachments that will not interfere with nor delay future repair, replacement, inspection and other construction to take place on or near the bridge (superstructure and substructure). c. Include in the design extra cable in a protected facility near the bridge so the bridge can be raised if necessary, and prevent delay to railroad operations. d. Design the fiber system so it does not obstruct the bridge bearings. See Figure 1-5-5. e. If practical, design the fiber system to be installed on the downstream side of the bridge. f. Fiber system must not be attached to a timber bridge, nor to the handrails of bridges. 5.5.3.1.15 Design handholes, splice boxes and manholes for appropriate loading conditions. In general, locations within 30 feet (9.14 meters) of track centerline should be designed for a Cooper E80 surcharge, while all other installations should withstand AASHTO H-20 highway loading requirements, in addition to soil-pressures. If a future main track is anticipated, the installation must be designed to handle surcharge loadings. 5.5.3.1.16 Show the location of fiber system marker signs on the design drawings, and submit a detail of the sign, including it’s color, for approval. This also applies to aerial marker signs. 1 3 5.5.3.2 Trenches and Excavations 5.5.3.2.1 Use shoring conforming to the most restrictive of railroad, state, OSHA, or AREMA standards in all excavations where required. Refer to OSHA standard in 29 CFR XVII Paragraph 1926.650. Submit shoring plans involving the railroad’s track or structures for approval prior to construction. See Figure 15-11. 5.5.3.2.2 All excavations and trenches will be attended or protected. Fence, fill or guard each site prior to leaving. Monitor shored trenches and excavations continuously during work for signs of instability and failure. 5.5.3.3 Bridges and Above Ground Installations 5.5.3.3.1 Fall protection is required for work performed on all bridges and above ground installations. Work on all bridges and structures on the railroad’s right-of-way is governed by the most restrictive of OSHA (29 CFR Parts 1910 and 1926), FRA Bridge Worker Safety Regulations (49 CFR Part 214), or state regulations. 5.5.3.3.2 Contractors performing work on bridges and above ground facilities on or over railroad property must submit written documentation certifying their employees have received proper training in fall protection prior to engaging in work on railroad property. The contractor must further satisfy the railroad © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-33 4 Roadway and Ballast representative that proper equipment and compliance with these standards will be adhered to on the job site. 5.5.3.4 Trenchless Installation of Fiber Systems 5.5.3.4.1 Submit plans for all bores that impact railroad’s right-of-way for approval. This includes both under-track bores and parallel-to-track bores. Detail the following on the plans: a. Boring methods and equipment; b. Depth(s) of the fiber system; c. Locations of bore pits relative to track centerline; d. Casing specifications. e. Excavation supports at bore pits 5.5.3.4.2 An extensive geotechnical analysis may be required to verify that railroad tracks will not be affected by the proposed bore. It is the responsibility of the fiber optic company or its contractor to provide such an analysis at the railroad’s request. 5.5.3.4.3 All bores are subject to railroad, federal, state and/or local requirements. 5.5.3.4.4 Ultimate approval of the boring process rests with the railroad. The railroad has the authority to delay the operation or establish additional requirements based on site characteristics. 5.5.3.4.5 Under-track bores are subject to the following requirements: a. Keep track bores under mainline tracks to a minimum. b. Locate the fiber system a minimum of 66 inches (1.68 meters) below the base of rail or natural ground, whichever is greatest. c. Encase in galvanized steel pipe or black iron pipe [Specified Minimum Yield Strength of 30,000 psi (241,318 kPa) or above] all fiber system lines under tracks in a single casing. For depths greater than 15 feet (4.57 meters) below the natural ground, Schedule 80 PVC pipe may be used in lieu of steel pipe or black iron pipe. Extend the casing a minimum of 30 feet (9.14 meters) from centerline of nearest track, measured perpendicular to the track, or longer, to stay out of cuts and/or fills. Multiple duct installations must use a single Schedule 80 or better casing for the bore. The crossing angle shall not be less than 45 degrees. d. If practical, design track bores to be greater than 150 feet (45.72 meters) from the nearest bridge, culvert, track switch (see Figure 1-5-10), building or other major structure. e. Design bore pits to be a minimum of 30 feet (9.14 meters) from centerline of nearest track when measured at right angles to the track. See Figure 1-5-7. Do not locate bore pits in the slope of a cut or fill section of the roadbed. Keep the bore pit size to a minimum. Location of crossings shall be in an area that does not require extensive shoring. See 5.5.3.2 Trenches and Excavations. Refer to Figure 1-5-11. f. Keep bore pits and other excavations to the minimum size necessary. 5.5.3.4.6 Generally accepted dry bore installation methods for under-track or parallel-to-track bores include: a. Jacking the casing through the subgrade. b. Dry auger boring. c. Dry mini-directional boring. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-34 AREMA Manual for Railway Engineering Pipelines Other methods will be considered on a case-by-case basis. Wet bores are not allowed for installing fiber systems on the railroad’s right-of-way. Wet bores in this context refer to the use of liquids to displace soil. 5.5.3.4.7 All boring methods are subject to the following conditions: a. The machine operator follows all railroad standards and OSHA regulations, including the use of grounding mats and other safety measures. b. The machine operator has control over the direction of the boring tool. c. Pull back methods use mandrels up to two inches (50.8 millimeters) larger than the diameter of the casing, up to a casing diameter of 8 inches (203.2 millimeters). d. Shallow bores, misdirected bores, or other unsuccessful bores are abandoned and filled at the discretion of the railroad. e. If a bore is unsuccessful, future attempts are made only with the approval of the railroad. f. Auger heads are not allowed more than six inches (152.4 millimeters) ahead of the casing being inserted. g. Any parallel-to-track bore that is made in either a cut back or fill section will be located a minimum of 60 inches (1.52 meters) below the toe of the ballast section or natural ground, whichever is lower. See Figure 1-5-12 & Figure 1-5-13. 5.5.3.4.8 Trenchless directional bores will be considered for under-track and parallel-to-track bores on a case-by-case basis, subject to these additional constraints. a. Under-track bores must be installed a minimum depth of 12 feet (3.66 meters) below the base of rail or 15 feet (4.57 meters) below the natural ground line, whichever is greater. b. An approved slurry must be kept to a minimum and only used for head lubrication and/or spoils return. Calculate anticipated slurry use and monitor slurry use during the bore operation to determine slurry loss into the surrounding soil. A bentonite slurry should be used to seal the hole with a minimum of 95% return. Should excessive slurry loss occur, operations must cease immediately. c. Maximum size of the finished hole is 10 inches (254 millimeters). d. Submit complete specifications for the machine to be used, including: 1 3 (1) Operating and maximum pressures of liquid at the drilling head; 4 (2) Water volume; (3) Source of water; (4) Power supply; (5) Type of reamer or cutting tool, number and size of holes/nozzles on the head, and method of head control; (6) Volume of anticipated spoils removal. e. Bore stems and cutting heads may have to be left in the ground if they can not be retrieved through the bore hole. Open excavation to retrieve the parts may not be possible. 5.5.3.4.9 Special conditions such as rock drilling that require the use of high-pressure air or water are subject to all of the conditions of this section and will be evaluated as they occur. Blasting is not allowed. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-35 Roadway and Ballast 5.5.3.4.10 Installation of fiber cable on pole lines within the railroad right-of-way will be considered on an individual basis. 5.5.3.4.11 Any overhead crossing of the track by the fiber system must at least adhere to AREMA Clearances. Fiber optic cables on polelines must be routinely inspected and maintained. 5.5.3.5 Repeater Stations (Regens) 5.5.3.5.1 Submit the regen design with the running line plan. Indicate all details of the site, such as building size, building access, concrete pad depth, soil removal and method conforming to environmental requirements, power supply, distance from track centerline, fences, all appurtenances, and distances from all road crossings. 5.5.3.5.2 Include with the power supply detail the following: voltages, distances relative to the mainline and other structures, overhead clearances and below ground dimensions. 5.5.3.5.3 Locate regens a safe distance from the nearest grade crossing. The governing minimum distance is the most stringent of either: (1) Local, state, or AASHTO clear sight distance requirements for grade crossings, or (2) 500 feet (152 meters). See Figure 1-5-8. These requirements could vary due to train and vehicle speeds at the crossings. 5.5.3.5.4 Do not locate regens under signal, communication, or power lines. 5.5.3.5.5 Locate regens a minimum of 50 feet (15.24 meters) from centerline of the nearest track to the nearest element of the regen facility, and avoid placement adjacent to track curves. See Figure 1-5-8. 5.5.3.5.6 Do not place regens where vision will be obstructed or interfere with railroad operations. Train signals must be clearly visible. 5.5.3.5.7 Regens may have to be located on private property to meet the requirements of this section. 5.5.3.6 Railplow Design 5.5.3.6.1 Routes that will utilize an on-track plow shall be designed approximately 11 feet (3.35 meters) from the centerline of track or beyond the toe of ballast line. 5.5.3.6.2 The running line shall not be permitted between centerline of tracks. Hand holes and pull boxes shall be no closer then 15 feet (4.57 meters) to the centerline of track. 5.5.3.6.3 Signal facilities should be avoided by trenching behind the facility. 5.5.3.6.4 The depth of the installation shall be 42 inches (1.07 meters) or greater. Other considerations may apply depending on the specific code. 5.5.3.6.5 The distance to centerline of track for bores and other excavations will be a minimum of 20 feet (6.10 meters) to accommodate railplow design and construction. Excavations in these areas must not violate train and structure surcharges. 5.5.3.6.6 Locate regens a minimum of 30 feet (9.14 meters) from centerline of the nearest track to the nearest element of the regen facility, and avoid placement adjacent to track curves. See Figure 1-5-8. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-36 AREMA Manual for Railway Engineering Pipelines 5.5.4 CONSTRUCTION (2001) 5.5.4.1 Complete arrangements must be made for safety training and protection of construction operations prior to any construction activity. 5.5.4.2 Obtain approval from the railroad for any deviation to the construction drawings and indicate such changes on the construction drawings. 5.5.4.3 Avoid the slope of cut or fill sections when designing the running line. Design the fiber system to run over the top of a cut section whenever possible. See Figure 1-5-9 & Figure 1-5-13. Note: Railplow construction may require cable to be in the bottom of the cut section. 5.5.4.4 If the fiber system has to be located in the ditch, place the system a minimum of 60 inches (1.52 meters) beyond the toe of the slope and a minimum of 60 inches (1.52 meters) below the bottom of the flow line. The fiber optic company may want to consider placing the fiber system at extra depth to allow for ditch cleaning. 5.5.4.5 Stabilize any waterways that have been plowed or cut. Use rip-rap or other approved erosion control methods. 5.5.4.6 Use OSHA and railroad approved shoring procedures on all trenches and excavations. See 5.5.3.2 Trenches and Excavations. 5.5.4.7 Backfill, cover or fence all excavations when unattended. 1 5.5.4.8 No equipment is allowed on any track ballast section. 5.5.4.9 Do not foul the track ballast with dirt or other foreign materials. 5.5.4.10 Do not store or place equipment, supplies, materials, tools, or other items within 25 feet (7.62 meters) of the nearest track centerline, or within 500 feet (152.4 meters) of road crossing. 3 5.5.4.11 Start cleanup and restoration of the railroad’s right-of-way immediately after the fiber system installation in each construction area and continue on a daily basis as the project progresses until complete. Ensure that any stumbling hazards are removed immediately. 5.5.4.12 Take care not to foul the ballast, block ditches, or culverts, or otherwise impede drainage. If chipping is approved, remove any brush or items that can not be chipped to 1 inch (2.54 centimeters). 5.5.4.13 Bridge attachments are generally not permitted. The fiber optic company must provide written justification prior to applying for permission to attach to the railroad bridge. Detailed drawings prepared by a registered structural engineer must be prepared for review and approval by the railroad. Install only railroad approved bridge attachments incorporating the following: a. The Fiber Optic Company is to install extra cable in a protective facility near the bridge so the bridge can be raised if necessary and without delay to railroad operations. b. Install the fiber system so as not to obstruct the bridge bearings. See Figure 1-5-5. The conduit should not be placed on top of the deck unless clearances can be obtained to stay outside the track structure for normal maintenance. Place the conduit on the outside of the superstructure by supporting it from the concrete deck, curb and/or walkway. Tie maintenance must not be impeded. c. Exercise care in trenching between the toe of the roadbed slope and bridge backwalls, typically by handdigging or dry boring. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-37 4 Roadway and Ballast d. Torch cutting or welding of bridge members is not allowed. Drill holes, if approved, are required for bracket attachment and specify high strength bolts (ASTM A325) for any brackets. Provide an expansion joint in detail. e. If brackets must be removed from the bridge, do not torch cut bolts. After removing the bracket, insert a bolt in the open hole and paint with galvanized paint. If the bridge is concrete, cut the bolt flush with the concrete surface. f. Touch-up any scratched galvanized bridge surfaces, including bracket attachments, with galvanized paint, including those areas of bridge steel that are to be covered by the brackets. The painted area should extend at least 2 inches (5.08 centimeters) beyond the contact surface. 5.5.4.14 Fall protection conforming to all Federal Railroad Administration and OSHA regulations is required for work performed on all bridges and above ground installations. 5.5.4.15 Install marker posts, handholes, splice boxes and manholes at least 30 feet (9.14 meters) from the centerline of mainline tracks or 15 feet (4.572 meters) from the centerline of other tracks. Install them so as not to create a stumbling hazard or to interfere with railroad operations. The signs should be placed at intervals that will permit viewing from any direction, as approved by railroad. 5.5.4.16 Railroad personnel will locate, remove, and replace all guy wires on railroad pole lines, if permitted. 5.5.4.17 Coordinate work on railroad poles with the railroad. 5.5.4.18 Follow applicable national electric codes for all pole work. 5.5.4.19 Obtain approval for all wire drops and splice locations from the railroad prior to construction. 5.5.4.20 Ensure all power lines on the poles have been de-energized. Check the poles for structural integrity before climbing. Use climbing equipment conforming to OSHA regulations. In addition, comply with federal, state, and local laws and regulations. 5.5.4.21 Do not throw trash into any excavations. 5.5.4.22 Contain all construction-generated waste material and remove it to an approved disposal site. This includes, but is not limited to, excavated foundations, old dump sites, debris, concrete or masonry obstructions, organic matter, rocks and boulders. 5.5.4.23 Remove all abandoned fiber optic cable systems from the right-of-way. Coordinate the method of cable removal with the railroad. 5.5.4.24 Regrade and clean construction sites to the condition they were before the project began. Reseed disturbed areas with indigenous grass species. Perform clean-up and restoration as the project progresses. 5.5.4.25 Repair or replace any disturbed fencing to equal or better condition. Immediately repair and/or monitor fences used to contain livestock. Ensure that livestock are not released onto the railroad’s rightof-way. 5.5.4.26 Do not operate heavy equipment on railroad’s paved roads located on the right-of-way without prior approval of the railroad. Use a protective covering over paved roads when crossing them with heavy equipment. Repair roads damaged or cut through. Coordinate such moves with the railroad. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-38 AREMA Manual for Railway Engineering Pipelines 5.5.4.27 When installing cable on top of cuts, do not operate equipment or install cable within 5 feet (1.52 meters) of the top of the slope, or the interceptor ditch. (See Figure 1-5-13.) 5.5.4.28 Comply with all applicable federal, state and local environmental laws and regulations. 5.5.4.29 Where Public Utilities Commission requirements meet or exceed the requirements of the Railroad, those requirements will apply. This would include but not be limited to, safety, clearances and walkways. 5.5.4.30 Maintain all existing facilities used to protect the public and/or railroad employees. Install additional facilities when needed to protect the public and/or railroad employees. 5.5.5 DOCUMENTATION (2001) 5.5.5.1 Construction drawings must have proper railroad engineering stationing ties, to result in acceptable As Built drawings. If construction plans are approved without the proper ties, it is the fiber optic company’s responsibility to provide them prior to As Built drawing approval. See Figure 1-5-4. Methodology for Equating Fiber Optic Cable Locations to Railroad Track & Right-of-Way Maps. 5.5.5.2 Include the following information on all construction plans and final As Built drawings: a. Alignment of the cable with railroad engineering stationing at each running line change or PI (point of intersection) including handholes, sign and markers. b. The depth of cable. c. Bridges (the railroad engineering stationing shown is measured from the inside backwall of a bridge). See Figure 1-5-5. Show the bridge milepost designation. d. Bridge attachments and their details. e. Culverts. f. Signals, signal houses and other signal facilities. g. All grade crossings, overhead viaducts and underpasses, including name of the street (public or private) and railroad mile marker designation. 1 3 h. All utility crossings (both underground and overhead), and all parallel utilities. i. Rivers, fences, and polelines. j. Railroad right-of-way limits. k. Railroad station names and mile markers. l. All mainline track, sidings, spur tracks and turnouts. 4 5.5.5.3 Include a separate detailed drawing for each regen station. Show all details of the site referenced to the mainline track, such as: a. Table of contents or list of drawings. b. Building size and distance building is from all road crossings. c. Distance the regen building is from centerline of all adjacent tracks. d. Power supply required for the regen building, including locations relative to the mainline, voltages, above and below ground dimensions. e. Building access. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-39 Roadway and Ballast f. Any other facility pertinent to the project. g. Location of fencing around the regen site, complete with dimensions. 5.5.5.4 Include the following additional information on construction drawings submitted to the Railroad: a. General notes along with the symbols and their meanings. b. A sheet showing all the special details. c. Small scale maps showing the overall cable route. d. Schematic showing regen sites. e. Sheet showing various methods of erosion control. f. Sheet showing details for backhoe trenching below a ditch, trench below a stream, direct burial for a ditch or creek crossing (plan and profile view). g. Sheet showing detail for placement of conduit in rock, including provisions for protecting Railroad ballast where it may be fouled by rock sawing operations. h. Include all boring and casing details. This includes, but is not limited to, dimensions, bore pit locations, and casing specifications. 5.5.5.5 Show all measurements of each of the above from and at right angles to the centerline of the nearest mainline track. Show on the drawing the distance to the next facility as measured along the centerline of the main track. 5.5.5.6 Note: Mile markers found in the field are representative of actual mileposts found on railroad rightof-way maps. These are intended to provide general locations of facilities for location by railroad personnel. These mile markers are not accurately located on railroad maps and should not be used to establish railroad stationing. Show them on your drawings for reference only. 5.5.5.7 Submit As Builts no later than 90 days after the completion of the installation of the fiber system on the Railroad’s right-of-way. 5.5.6 MAINTENANCE (2001) 5.5.6.1 Emergency Maintenance In the event emergency work is required, the following procedures apply: a. Call the railroad for emergency approval. The railroad will determine inspector/flagger needs based on site conditions. b. Perform emergency work only when appropriate flagging/inspection personnel are on site. c. Following the completion of emergency repairs to restore the fiber system to service, permanent restoration of the fiber system falls under the conditions of the following section. 5.5.6.2 Regular Maintenance 5.5.6.2.1 Notify the railroad prior to entering the railroad’s right-of-way to repair or maintain the fiber system. 5.5.6.2.2 The methods and procedures of all maintenance and repair work are subject to the consent and approval of the railroad. Submit to the railroad for approval plans for any work not previously detailed in © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-40 AREMA Manual for Railway Engineering Pipelines the approved Construction Plans. Include (as applicable) drawings showing the plan, elevation, details, Railroad engineering stationing and methods of the proposed construction, installation, maintenance, repair, replacement or other work. 5.5.6.2.3 Fiber optic company crew locations and the number of crews may be restricted depending on railroad flagger availability, job site access and adequate radio communications. 5.5.6.2.4 Ensure that all representatives and employees of the fiber optic company and its contractor have been safety trained. 5.5.6.2.5 Follow the construction guidelines in Article 5.5.4 Construction (2001) for any repair or maintenance work involving alteration of the fiber system. 5.5.6.2.6 Never allow work to disrupt rail operations, including but not limited to, train operations, facilities maintenance and communications. 5.5.6.2.7 Do not store or place equipment, supplies, materials, tools, or other items within 25 feet (7.62 meters) of the nearest track centerline unless the railroad approves such placement. 5.5.6.2.8 Begin clean-up and restoration immediately upon completion of maintenance operations. Restore the railroad’s right-of-way to the same condition as prior to the maintenance being performed. 5.5.6.2.9 Remove abandoned fiber optic cable, see Article 5.5.4 Construction (2001). If cable is not removed, maintain records of the location of abandoned cable. 1 5.5.7 DEFINITIONS (2001) Aerial Marker Sign: A large sign, typically in the shape of a “V” that can be observed from the air, used for aerial location and inspection of the fiber system. As Built: A drawing, depicting the actual location of the fiber cable in relation to the Railroad, having proper documentation for approval by the Railroad. 3 Ballast: The rock that supports the track and ties. This rock is groomed to keep the track in place, drain water away from the track and distribute the weight of trains to surrounding soil. Do Not Disturb! Branchline: A secondary route to the Railroad that, for safety reasons, should be treated as a primary line. Bridge Attachment: A Railroad approved method of affixing the fiber system to one of the Railroad’s bridges. Bridge Backwall: The topmost portion of an abutment above the elevation of the bridge bearing, functioning primarily as a retaining wall for the roadbed. Bridge Bearing: The contact area and/or physical connection between bridge girders and bridge abutments or piers (Figure 1-5-5). Casing: A secondary, independent, rigid covering used to protect the fiber system and the roadbed when installed under the Railroad’s tracks. Car: Any vehicle that can move on the track structure and is not self-propelled. Centerline of Track: An imaginary line, that runs down the center of the two rails of a track. Conduit: An independent tube or duct system used to house one or more fiber optic cables. Contractor: Any fiber optic company authorized worker, other than a railroad employee, who is working on railroad property as a fiber optic company representative or agent. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-41 4 Roadway and Ballast Cut: A section of earth that has been excavated to allow construction of the Railroad’s track where an embankment remains on one or both sides of the track. Directional Bore: A method that controls the direction of boring and eliminates conventional bore pits allowing for a longer bore length than conventional methods. Dispatcher: A Railroad employee responsible for authorizing all track use, including train movements and maintenance. Drawings: A graphic representation of proposed fiber routes, detailed construction plans, or As Builts. Dry Bore: A method that utilizes conventional bore pits without using a liquid to displace soil. Encased: A term used to indicate that the fiber system has a secondary, independent, rigid, protective covering. Engine: The vehicle used to pull cars. Typically this refers to the locomotive, but can be any self-propelled vehicle. Excavation: Any removal of earth to allow installation of the fiber system. Fall Protection: A requirement by the FRA, that ensures training and protection for work performed on any structure that is at a height of 12 feet (3.66 meters) or more above water or ground, and/or while working at a height of 12 feet (3.66 meters) or more. Fiber Optic Company: The company that enters into the agreement with the Railroad and has the ultimate responsibility for the fiber system. This includes any contractor, employee, or consultant hired by that company. Fill: A section of earth built up to support the Railroad’s track structure. Flagger: A railroad employee, who provides for the safe use of the Railroad’s right-of-way. Foul the Ballast: Anything that contaminates the ballast section of the roadbed and inhibits the ballast from supporting the track, draining water, or suppressing weed growth. Foul the Track: Any obstruction that renders the track system unsafe for train passage. Grout: A cementitious or epoxy substance used to repair concrete, fill holes in concrete, or to anchor bolts, rods, etc., in concrete. Grout must be approved by the Railroad prior to use. Handhole: A buried facility that can contain a splice or extra cable. Hy Rail: A vehicle, typically driven on highways, that has a specially manufactured attachment, that allow the vehicle to travel on railroad tracks. Industry Track: A secondary track designed to allow access to industries along the main track. Innerduct: Flexible independent tubes inside a conduit. Job Site: Any area where work is performed, where materials and equipment are stored, or which employees access during the fiber project. Locate: The determination in the field of the depth and horizontal position of fiber optic systems or other underground utilities. Mainline: The primary track used by trains. Some of the routes have double, triple and quadruple mainline tracks. Marker signs: Signs placed by the fiber optic company indicate a fiber system is in the area, provide a toll free number for information regarding the system, and provide the fiber optic company’s name. Milemarkers: Field indicators of approximate distance from a specific point on the Railroad system used for approximate locations of Railroad facilities. They are not to be used to establish railroad stationing. Milepost: A theoretical breakdown of rail lines into mile-long segments. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-42 AREMA Manual for Railway Engineering Pipelines On Track Safety: A set of safety rules, developed and promulgated by the FRA, that must be complied with to work on or near railroad property. Specific training and obedience to these rules is a requirement of the FRA. Where individual railroad rules are more stringent, those rules shall apply. Significant fines and the loss of your permission to work on railroad right-of-way, can result from the violation of these rules. Point of Intersection: A point on a map or drawing indicating the location of a curve in the fiber system. The point is the vertex of an angle formed by the intersection of two sequential, non-parallel segments of the fiber system. Protected Facility: A handhole, manhole or box that can withstand external pressures and protect the fiber system. Pull Box: A facility generally used to pull cable through a conduit system. Railplow: Rail mounted plowing equipment pulled or powered by locomotive power. Regen: An acronym for a regeneration facility. Typically a building along the fiber system route housing equipment. Regen facility: The Regen building and all of its appurtenances such as fences, signs, posts, or other physical features. Right-of-way: Land that the Railroad owns or owns an interest in that contains facilities for train operations and which is utilized in the performance of the fiber project. Roadbed: The graded area beneath and on either side of the track. Running Line: Proposed or existing location of the fiber system. Safety Training: A session conducted by a qualified railroad representative, or it’s agent at which railroad rules and regulations are presented and discussed. 1 Shoring: Methods and materials used to prevent the collapse of the earthen walls of excavations. Siding: A secondary track used for the passing of trains on single-track routes. 3 Signal: A Railroad facility used to inform Railroad personnel of track conditions. Splice: A point in the fiber optic system running line where cables are fused together to create a continuous system. Spur Track: A secondary track designed to allow access to industries along the main track. Switch: A moveable track device that allows trains to transfer from one track to another, encompassing the distance from the point of switch to the point of frog. (See Figure 1-5-10). Tracks: The rails, ties and ballast and roadbed that compose the traveling surface used by trains. Track Structure: The rails, ties, ballast and roadbed that compose the traveling surface used by trains. Trains: One or more engines coupled together, with or without cars that use the Railroad’s tracks. Train Movement: Any motion of engines and/or cars over the Railroad’s tracks. Trench: A narrow section of earth removed to allow installation of the fiber system. Valuation Map: A Railroad map depicting the Railroad’s facilities and engineering stationing. Wet Bores: Are bores that use liquid to displace soil. Yard: A collection of secondary tracks used to store equipment (cars, engines, maintenance machines, etc.), assemble or disassemble trains, and/or conduct other Railroad operations. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-43 4 Roadway and Ballast 5.5.8 ABBREVIATIONS (2001) AASHTO: American Association of State Highway and Transportation Officials ANSI: American National Standards Institute AREMA: American Railway Engineering and Maintenance-of-Way Association ASTM: American Society for Testing and Material BIP: Black Iron Pipe Br.: Bridge CE: Chief Engineer CIP: Corrugated Iron Pipe CL/Trk: Center Line of Track CMP: Corrugated Metal Pipe Conc.: Concrete C/L: centerline FIBOCO: An acronym for the fiber optic company FRA: Federal Railroad Administration F/L: Flow Line GSP: Galvanized Steel Pipe HDPE: High Density Polyethylene Plastic HH: Handhole Lt.: Left MH: Manhole MM: Mile Marker MP: MilePost OSHA: Occupational Health & Safety Administration PI: Point of Intersection PVC: Polyvinyl Chloride Plastic Rt.: Right R/L: Running Line R/W: Right-of-way R-O-W: Right-of-way Xing: Crossing 5.5.9 APPENDIX (2001) List of Exhibits: © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-44 AREMA Manual for Railway Engineering Pipelines A: METHODOLOGY FOR EQUATING FIBER OPTIC CABLE LOCATIONS TO RAILROAD TRACK AND RIGHT-OF-WAY MAPS B: BRIDGE DEFINITION C: CABLE DEPTH AROUND CULVERTS AND DITCHES D: BORE PIT LOCATION E: REGEN LOCATION F: CONVENTIONAL FILL INSTALLATION G: STANDARD TURNOUT (TRACK SWITCH) H: GENERAL SHORING REQUIREMENTS I: DIRECTIONAL BORE FILL INSTALLATION J: INSTALLATION ON TOP OF CUT 1 3 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-45 Roadway and Ballast 1-5-46 AREMA Manual for Railway Engineering © 2010, American Railway Engineering and Maintenance-of-Way Association Figure 1-5-4. Methodology for Equating Fiber Optic Cable Locations to Railroad Track & Right-of-Way Maps Pipelines 1 3 4 Figure 1-5-5. Bridge Definition © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-47 Roadway and Ballast Figure 1-5-6. Cable Depth Around Culverts and Ditches © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-48 AREMA Manual for Railway Engineering Pipelines 1 3 4 Figure 1-5-7. Bore Pit Location © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-5-49 Roadway and Ballast Figure 1-5-8. Regen Location © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-50 AREMA Manual for Railway Engineering © 2009, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering Pipelines 1-5-51 Figure 1-5-9. Conventional Fill Installation Roadway and Ballast Figure 1-5-10. Standard Turnout © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-52 AREMA Manual for Railway Engineering © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering Pipelines 1-5-53 Figure 1-5-11. General Shoring Requirements Roadway and Ballast 1-5-54 AREMA Manual for Railway Engineering © 2010, American Railway Engineering and Maintenance-of-Way Association Figure 1-5-12. Fill Installation Directional Bore © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering Pipelines 1-5-55 Figure 1-5-13. Installation on Top of Cut Roadway and Ballast THIS PAGE INTENTIONALLY LEFT BLANK. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-5-56 AREMA Manual for Railway Engineering 1 Part 6 Fences1 — 1994 — TABLE OF CONTENTS Section/Article Description Page 6.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6-3 6.2 Specifications for Wood Fence Posts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.1 Material (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.2 Physical Requirements (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.3 Design (1987) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.4 Manufacture (1987) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.5 Inspection (1991) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.6 Delivery (1991). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.7 Preservative Treatment (1991) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6-4 1-6-4 1-6-4 1-6-5 1-6-5 1-6-6 1-6-6 1-6-6 6.3 Specifications for Concrete Fence Posts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.1 Materials (1991). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.2 Proportioning and Mixing (1991) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.3 Manufacturer (1991) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6-6 1-6-6 1-6-7 1-6-7 6.4 Specification for Metal Fence Posts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.1 Classes (1987) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.2 Material (1987) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.3 Workmanship (1987) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.4 Finish (1987) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.5 Special Fabrication for Line Posts (1987) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.6 Special Fabrication for End, Corner, and Gate Posts (1987) . . . . . . . . . . . . . . . . . . . . . . . 6.4.7 Weights and Shapes (1987) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.8 Inspection (1987) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6-10 1-6-10 1-6-10 1-6-10 1-6-10 1-6-11 1-6-11 1-6-11 1-6-13 6.5 Specifications for Right-of-way Fences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.1 General (1987) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.2 Material (1991) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.3 Erection (1991) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6-13 1-6-13 1-6-17 1-6-18 1 References, Vol. 43, 1942, pp. 510, 731; Vol. 54, 1953, pp. 1091, 1385; Vol. 63, 1962, pp. 590, 752; Vol. 67, 1966, pp. 537, 740; Vol. 88, 1987, pp. 34; Vol. 92, 1991, p. 40; Vol. 94, 1994, p. 31. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-6-1 1 3 Roadway and Ballast TABLE OF CONTENTS (CONT) Section/Article Description Page 6.6 Stock Guards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6.1 General (1991) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6-20 1-6-20 6.7 Methods of Controlling Drifting Snow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.7.1 Justification and Scope (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.7.2 References (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.7.3 Definitions and Terminology (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.7.4 Specifications for Roadbed Geometry (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.7.5 Specifications for Clearing and Mowing Vegetation (1994) . . . . . . . . . . . . . . . . . . . . . . . . 6.7.6 Specifications for Placement of Bungalows and Other Structures (1994) . . . . . . . . . . . . 6.7.7 Temporary Control Measures (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6-21 1-6-21 1-6-21 1-6-21 1-6-22 1-6-23 1-6-23 1-6-23 6.8 Specifications for Snow Fences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.8.1 Effectiveness and Applications (1994). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.8.2 Structural Fences (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.8.3 Tree and Shrub Plantings (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6-24 1-6-24 1-6-24 1-6-39 LIST OF FIGURES Figure 1-6-1 1-6-2 1-6-3 1-6-4 1-6-5 1-6-6 1-6-7 1-6-8 1-6-9 1-6-10 1-6-11 1-6-12 1-6-13 1-6-14 1-6-15 1-6-16 1-6-17 1-6-18 1-6-19 1-6-20 1-6-21 1-6-22 Description Page Plan of Concrete Fence Posts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical Cross Sections of Steel Fence Posts Commonly Available. . . . . . . . . . . . . . . . . . . . . . . Class A Fence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Class B Fence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Class C Fence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Class D Fence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Guidelines for Minimum Height of Roadbed above Grade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Recommended Cut Section to Prevent Snowdrift Encroachment . . . . . . . . . . . . . . . . . . . . . . . Snow Storage Capacity Versus Effective Fence Height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Definition of Terms in the Calculation of Snow Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shape of Equilibrium Drifts Formed by 50% Porous Snow Fences Having Effective Height H. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Illustration of Three-dimensional Rounding of Drifts at Fence Ends . . . . . . . . . . . . . . . . . . . . Placement of Fences when Wind Angle is less than 65 degrees . . . . . . . . . . . . . . . . . . . . . . . Stepping-down Height at Fence Ends Allows Fences to be Placed Closer to Track and Improves Effectiveness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Herringbone Arrangement is Effective in Reducing Drifting Snow When Wind is Aligned Parallel to Track . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Extending Snow Fences Beyond Protected Area Compensates for “End Effect” and Variations in Prevailing Wind Direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Effect of Bottom Gap on Storage Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . How Snow Storage Capacity Varies With Snow Fence Porosity . . . . . . . . . . . . . . . . . . . . . . . . How Length of Downwind Drift Varies With Snow Fence Porosity . . . . . . . . . . . . . . . . . . . . . Generic Plan for the “Wyoming” Snow Fence with Vertical Height H . . . . . . . . . . . . . . . . . . . U-clip Used to Attach “Wyoming” Fence to Re-bar Anchor . . . . . . . . . . . . . . . . . . . . . . . . . . . . Panel Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6-8 1-6-11 1-6-13 1-6-14 1-6-15 1-6-16 1-6-22 1-6-23 1-6-25 1-6-25 1-6-26 1-6-26 1-6-27 1-6-28 1-6-28 1-6-29 1-6-30 1-6-31 1-6-31 1-6-33 1-6-33 1-6-35 © 2010, American Railway Engineering and Maintenance-of-Way Association 1-6-2 AREMA Manual for Railway Engineering Fences LIST OF FIGURES (CONT) Section/Article 1-6-23 1-6-24 1-6-25 1-6-26 Description Plastic Fencing Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods for Accommodating Slope Changes Using Synthetic Materials . . . . . . . . . . . . . . . . . . Recommended Planting Arrangement for Locations Having Moderate Snow Transport. . . . . Snowbreak Forest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 1-6-38 1-6-38 1-6-39 1-6-40 LIST OF TABLES Table 1-6-1 1-6-2 1-6-3 1-6-4 1-6-5 1-6-6 1-6-7 1-6-8 1-6-9 1-6-10 1-6-11 Description Design and Dimensions of Fence Posts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Compressive Strength Variances. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Curing Duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Metal Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nominal Weights of Line Posts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nominal Weights of End, Gate and Corner Assemblies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wire Tensile Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Range of Fence Heights Required in U.S.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . “Wyoming-Type” Snow Fence Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wood Pole Sizes and Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Embedment Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 1-6-5 1-6-7 1-6-9 1-6-10 1-6-12 1-6-12 1-6-17 1-6-25 1-6-34 1-6-36 1-6-36 1 SECTION 6.1 GENERAL This Part of the Chapter is prepared for the purpose of presenting specifications for various types of fencing and components. 3 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-6-3 Roadway and Ballast SECTION 6.2 SPECIFICATIONS FOR WOOD FENCE POSTS 6.2.1 MATERIAL (1994) 6.2.1.1 Kinds of Wood The manufacturer may furnish posts made from any of the following woods listed unless otherwise specified by the purchaser. With the exception of Redwood, all kinds of wood should receive preservative treatment. Black Locust Black Walnut Ash Hackberry Cypress Heart Yellow Pine Beech Maple Catalpa Larch Birch Red Oak Cedar Red Mulberry Black Gum Sap Yellow Pine Chestnut Redwood Cherry Sap Fir Douglas Fir White Oak Elm Sycamore Hickory 6.2.2 PHYSICAL REQUIREMENTS (1994) 6.2.2.1 Defect1 Posts shall be free from the following defects: decay, excessive crook, wane on rectangular posts, holes in top of post, numerous holes, large knots, large shakes and splits. 6.2.2.2 Defects Allowable1 a. In round cedar posts, pipe or stump rot up to 0.75 inch in diameter in butt end. b. Peck in cypress up to limitation of holes. c. Crook that does not exceed 3 inches measured perpendicular between the longitudinal axis and a straight line from the center of one end to the center of the other end. d. Wane on rectangular posts not exceeding one-fourth of the dimension of the faces. e. Holes other than in top of post not exceeding 1 inch in diameter and 3 inches deep. f. Numerous holes that are not damaging in effect. g. Knots in round posts whose average diameter is less than one-third the diameter of post. h. Knots in rectangular posts whose average diameter is less than 0.25 the width of surface in which the knot appears. i. 1 Numerous knots that are not damaging in effect. For definition of terms please see “Definition of Terms Used in Describing Standard Grades for Lumber,” Chapter 7, Timber Structures, Part 1, Material Specifications for Lumber, Timber, Engineered Wood Products, Timber Piles, Fasteners, Timber Bridge Ties and Recommendations for Fire-Retardant Coating for Creosoted Wood. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-6-4 AREMA Manual for Railway Engineering Fences j. Large shakes in rectangular posts whose maximum dimension between parallel lines does not exceed 0.25 of the minimum thickness of post. k. In round posts shakes not damaging in effect. l. Splits not damaging in effect. 6.2.3 DESIGN (1987) 6.2.3.1 General Posts shall be of the size and dimensions specified in the order. 6.2.3.2 Dimensions All posts shall be in accordance with the designs and dimensions shown in Table 1-6-1. Table 1-6-1. Design and Dimensions of Fence Posts Dimensions Intermediate or Line Posts Design At Small End End, Corner, Anchor and Gate Posts Length At Small End Length 4 inch diameter 7 feet 8 inch diameter 8 feet 5 inch diameter 8 feet – – Rectangular 4" × 4" 7 feet 8" × 8" 8 feet 5" × 5" 8 feet – – 19 inch perimeter 7 feet – – 21 inch perimeter 8 feet – – 19 inch perimeter 7 feet – – 21 inch perimeter 8 feet – – Round Halved Quartered 1 3 4 6.2.4 MANUFACTURE (1987) 6.2.4.1 General Requirements All posts shall be straight, well manufactured, of natural taper, free from projections and cut square at ends unless small end is roofed. Inner skin must be removed and roofing or gaining of treated posts shall be done before treatment. 6.2.4.2 Tolerances a. Posts shall not be more than 1 inch shorter nor 3 inches longer than the length specified. b. Posts shall not be more than 1/4 inch smaller nor more than 1 inch larger than the diameters, widths and perimeters specified. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-6-5 Roadway and Ballast 6.2.5 INSPECTION (1991) 6.2.5.1 General All materials and all processes of manufacture shall be subject to inspection and approval at all times. Free access shall be provided during regular working hours for all authorized inspectors to all parts of the manufacturing facility in which the posts or materials are made, stored or prepared. 6.2.5.2 Manner Inspectors will make a reasonably close inspection of each post, which shall be judged independently, without regard for decisions on others in the same lot. Posts too soiled for ready examination will be rejected. Posts shall be turned over as inspected. 6.2.6 DELIVERY (1991) 6.2.6.1 Separated as Specified Posts shall be separated according to the kind of wood, shape and size or as may be required in the order for them. 6.2.7 PRESERVATIVE TREATMENT (1991) 6.2.7.1 Specifications Posts shall be treated in accordance with the AREMA specifications see Chapter 30, Ties, Part 1, General Considerations. SECTION 6.3 SPECIFICATIONS FOR CONCRETE FENCE POSTS 6.3.1 MATERIALS (1991) Cement, aggregate, water and metal reinforcement shall conform in quality to the AREMA specifications see, Chapter 8, Concrete Structures and Foundations, Part 1, Materials, Tests and Construction Requirements, with the following exceptions: • The maximum size of aggregate shall be not more than three-quarters the clear embedment distance. • Reinforcement shall be in the form of round or square bars or cold drawn steel wire. Crimped, stranded or flat reinforcement shall not be used. • Where choices can be made between sizes of reinforcement, it is preferable to use the larger number of smaller bars. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-6-6 AREMA Manual for Railway Engineering Fences 6.3.2 PROPORTIONING AND MIXING (1991) Proportioning and mixing concrete shall be in accordance with the AREMA specifications see, Chapter 8, Concrete Structures and Foundations, Part 1, Materials, Tests and Construction Requirements, with the exception that the compressive strength of concrete shall vary with the amount of clear imbedment of reinforcement, as shown in Table 1-6-2. Table 1-6-2. Compressive Strength Variances Clear Imbedment Inches Class of Concrete Compression Strength Psi at 28 Days Gallons of Water per Sack of Cement 3/4 3500 5.00 1/2 4000 4.50 3/8 4500 4.00 6.3.3 MANUFACTURER (1991) 6.3.3.1 General 1 The concrete fence post shall be manufactured in accordance with the dimensions shown in Figure 1-6-1. 6.3.3.2 Molds Molds shall be substantial, true to plan and preferably of metal. They shall be thoroughly cleaned before concrete is placed. 3 6.3.3.3 Placing Reinforcing The reinforcing shall be securely held in position during the placing and setting of concrete. Spacers that would cause distinct lines of cleavage shall not be used. 6.3.3.4 Compacting Concrete shall be thoroughly compacted into the molds and around the reinforcing. This is best accomplished by high frequency vibration of the molds. 6.3.3.5 Finish Imperfections such as exposure of reinforcing, sand streaking due to loss or lack of cement paste, honeycomb clusters or pockets of coarse aggregate without proper mixture of the finer components of concrete, cracks or other evidence of improper mixing or faulty construction shall cause the rejection of the post. Patching will not be permitted. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-6-7 4 Roadway and Ballast Figure 1-6-1. Plan of Concrete Fence Posts © 2010, American Railway Engineering and Maintenance-of-Way Association 1-6-8 AREMA Manual for Railway Engineering Fences 6.3.3.6 Curing a. Curing shall start immediately after placement of concrete and shall extend for the following periods of time depending upon the temperature being maintained uniformly during the curing period shown in Table 1-63. Table 1-6-3. Curing Duration Approximate Temperature Degree F b. Curing Period in Days 50 14 70 10 90 7 120 2 Temperatures exceeding 140 degrees F must not be used. No evaporation or other loss of moisture from the concrete shall be permitted during curing period, or while cooling off after heat curing. 6.3.3.7 Inspection All materials and all processes of manufacture shall be subject to inspection and approval at all times. Free access shall be provided for all authorized inspectors to all parts of the plant in which the posts or the materials are made, stored or prepared. 1 6.3.3.8 Tests a. b. Posts should be carefully made so as to secure a uniform strength in substantially all posts, and this strength should usually be such that the post will withstand a force of not less than 180 lb at right angles to the axis of the post, the post acting as a cantilever beam supported at the ground line and the force being applied 5 feet above the ground line. 3 During the curing or cooling off period, posts submerged in water for 2 hr and wiped off, shall not show an increase in weight. 6.3.3.9 Patents 4 The manufacturer shall pay all royalties for the use of patented designs or devices or forms of construction and protect the railway company from all claims of infringement or liability for use of such patents. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-6-9 Roadway and Ballast SECTION 6.4 SPECIFICATION FOR METAL FENCE POSTS 6.4.1 CLASSES (1987) Metal fence posts shall be divided into two classes: a. Posts which support the straightaway body of the fence shall be designated as line posts. b. Such other special posts as are needed at the end or corner of the fence and at gates, shall be designated as end, corner, and gate posts. 6.4.2 MATERIAL (1987) Posts shall be fabricated from hot rolled steel sections meeting either of the requirements shown in Table 1-6-4. Table 1-6-4. Metal Quality Tensile Properties Grade Hot rolled carbon steel-minimum carbon content 0.35% Hot rolled rail steel (Note 1) Yield Str. Psi Ult. Str. Psi 40,000 min 70,000 min 50,000 80,000 min Note 1: As defined in the U.S. Bureau of Standards Commercial Standard CS150-48, rail steel products shall be rolled from standard Tee-Section steel Rails. No other material such as those known by terms “rerolled”, “rail steel equivalent”, and “rail steel quality” shall be substituted. 6.4.3 WORKMANSHIP (1987) All posts shall be smoothly rolled or formed and shall be straight throughout their length. Each finished post shall be free from burrs or other deformation caused by fabrication. They shall also be free from slivers, depressions, seams, crop ends and evidence of being burnt. (The above does not refer to rough places caused by zinc coating when galvanized.) Excessive bow, camber, twist, or other injurious defects shall be considered cause for rejection of such posts. 6.4.4 FINISH (1987) a. Painted posts shall be cleaned of all loose scale prior to finishing and one or more coats of high grade, weather-resistant, special steel paint or enamel shall be applied and baked. b. Galvanized posts shall be galvanized by the hot dip process and shall possess a uniform coating of Prime Western spelter or better grade, with not less than 2 oz per square foot of surface. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-6-10 AREMA Manual for Railway Engineering Fences 6.4.5 SPECIAL FABRICATION FOR LINE POSTS (1987) a. Line posts shall be fabricated to the section agreed upon by the purchaser. b. Line posts shall be tee, U, Y, channel, or other suitable section and shall have corrugations, knobs, notches, holes, or studs so placed and constructed as to engage at least 12 fence line wires in proper position in a height of 5 feet above the surface of the ground. Posts may be punched with holes in such position and of such size as will not impair the strength of the post. c. If the posts are not so designed as to make anchorage for alignment unnecessary an anchorage device shall be rigidly fabricated to bottom portion of posts. Anchor plates on line posts shall weigh 0.67 lb or more each and shall be tapered to facilitate driving. Anchor plates shall be clamped, welded, or riveted to the posts in a substantial manner to prevent displacement of anchor plates when posts are driven. d. All posts shall permit the refastening of the wire at least five times without damage to the connection appliance, if an integral part of the post. e. All posts shall be capable of being driven in ordinary earth without injury to the post. f. All posts shall have sufficient length so that when installed with the required height above ground, 1/3 of the total length shall be underground, providing that the post shall extend into the ground not less than 21/2 feet. 6.4.6 SPECIAL FABRICATION FOR END, CORNER, AND GATE POSTS (1987) End, corner, and gate post assemblies shall be angle sections consisting of 2-1/2" × 2-1/2" × 1/4" uprights and the required number of braces, either 2" × 2" × 1/4" or an alternate of approximately equal weight, such as a 2-1/2" × 2-1/2" of appropriate thickness. For joining the uprights and braces shall be supplied with the necessary holes and bolts of standard commercial quality or other satisfactory substitute, such as castings. All posts shall have sufficient length to permit installing 3 feet into the ground. 3 6.4.7 WEIGHTS AND SHAPES (1987) a. Sketches shown are suggestive of typical cross sections commonly supplied. Sizes shown in Figure 1-6-2 are approximately half scale, however, both overall and thickness dimensions will vary with individual post designs. All sections will conform to standard nominal weight of 1.33 lb per foot. b. Sections shown do not illustrate features for attaching fence wire and preventing vertical displacement, such as rolled in lugs, notches, studs, corrugations, or punched oval, round or slotted holes. Figure 1-6-2. Typical Cross Sections of Steel Fence Posts Commonly Available © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1 1-6-11 4 Roadway and Ballast 6.4.7.1 Nominal Weight a. Line posts shall have a nominal weight of 1.33 lb per foot, exclusive of anchor plate. b. Angle type end, corner and gate posts shall have a nominal weight of 4.10 lb per ft for upright members and bracing members shall have a nominal weight of 3.19 lb per ft. c. Permissible variation in weight shall be a maximum of 3-1/2% over or under nominal weight shown in Table 1-6-5 and Table 1-6-6. Weights are to be taken on the total lot of posts in each order. d. Permissible variation in length shall be a maximum of 1 inch, under and 2 inches over the designated length of the post. Table 1-6-5. Nominal Weights of Line Posts Post Lengths Feet Weight (Note 1) Pounds 5 7.32 5-1/2 7.99 6 8.65 6-1/2 9.32 7 9.98 7-1/2 10.65 8 11.31 Note 1: Includes anchor plates and paint. Table 1-6-6. Nominal Weights of End, Gate and Corner Assemblies Post Assembly Length Feet Weight (Note 1) Pounds End or gate (1 brace) 7 51 Corner (2 braces) 7 73 End or gate (1 brace) 8 58 Corner (2 braces) 8 84 End or gate (1 brace) 9 66 Corner (2 braces) 9 94 Note 1: Includes weight of paint and bolts. 6.4.7.2 Formed Wire Fasteners Each line post shall be furnished with not less than 5 suitable galvanized wire fasteners or clamps of not less than 0.120 inch in diameter for attaching the fence wires to the post. Ordinary wire staples will not be considered suitable fasteners. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-6-12 AREMA Manual for Railway Engineering Fences 6.4.8 INSPECTION (1987) Inspection and approval of the posts shall be made by the engineer or other authorized representative of the purchaser. Such inspection shall be made at the plant of the manufacturer, who will allow the inspector access to all operations involved and shall facilitate as much as possible the work of inspection and provide necessary facilities for inspection. Posts selected by the inspector at random, shall be inspected, and if they meet the requirements, the lot shall be accepted. SECTION 6.5 SPECIFICATIONS FOR RIGHT-OF-WAY FENCES 6.5.1 GENERAL (1987) 6.5.1.1 Classes The height and construction of right-of-way fences shall conform to statutory requirements. Standard right-of-way fences shall be divided into four classes. 6.5.1.2 Class A Fence (See Figure 1-6-3) a. Class A fence shall consist of 9 longitudinal smooth galvanized steel wires; the longitudinal and stay wires shall be No. 9 gage. b. The spacing of the longitudinal wires (commencing at the bottom) shall be 4, 4-1/2, 5, 5-1/2, 6, 7, 8 and 9 inches. The bottom wire shall be 5 inches above the ground and the stay wires shall be spaced 12 inches apart. c. When used as a hog-tight fence, a strand of barbed wire shall be added 2-1/2 inches below the woven wire. 1 3 4 Figure 1-6-3. Class A Fence © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-6-13 Roadway and Ballast 6.5.1.3 Class B Fence (Figure 1-6-4) a. Class B fence shall consist of 7 longitudinal smooth galvanized steel wires; the longitudinal and stay wires shall be No. 9 gage. b. The spacing of the longitudinal wires, commencing at the bottom shall be 6-1/2, 7, 7-1/2, 8, 8-1/2 and 9 inches. The bottom wire shall be 7 inches above the ground and stay wires shall be spaced 12 inches apart. Figure 1-6-4. Class B Fence © 2010, American Railway Engineering and Maintenance-of-Way Association 1-6-14 AREMA Manual for Railway Engineering Fences 6.5.1.4 Class C Fence (Figure 1-6-5) Class C Fence shall consist of woven wire fencing 25-1/2 inches high with 3 strands of barbed wire above. The woven wire fencing shall consist of 7 longitudinal, smooth galvanized steel wires. The longitudinal and stay wires shall be No. 9 gage and the stay wires shall be 12 inches apart. The spacing of the longitudinal wires, commencing at the bottom, shall be 3, 3-1/2, 4, 4-1/2, 5 and 5-1/2 inches, and the bottom wire shall be 2 inches above the ground. The spacing of the barbed wires above the woven wire shall be 4-1/2, 10 and 12 inches. 1 3 Figure 1-6-5. Class C Fence 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-6-15 Roadway and Ballast 6.5.1.5 Class D Fence (Figure 1-6-6) a. Class D Fence shall consist of 5 strands of galvanized steel ribbon, smooth round or barbed wire fencing. b. The spacing of the wires, commencing at the bottom, shall be 10, 10, 12 and 12 inches. The bottom wire shall be 10 inches above the ground. c. The longitudinal wires of all woven wire fencing under Classes A, B and C shall be provided with tension curves to take up expansion and contraction. Figure 1-6-6. Class D Fence © 2010, American Railway Engineering and Maintenance-of-Way Association 1-6-16 AREMA Manual for Railway Engineering Fences 6.5.2 MATERIAL (1991) 6.5.2.1 Intermediate or Line Posts See Section 6.2, Specifications for Wood Fence Posts, Section 6.3, Specifications for Concrete Fence Posts, Section 6.4, Specification for Metal Fence Posts. 6.5.2.2 End, Corner, Anchor and Gate Posts See Section 6.2, Specifications for Wood Fence Posts, Section 6.3, Specifications for Concrete Fence Posts, Section 6.4, Specification for Metal Fence Posts. 6.5.2.3 Braces Braces for end, corner, anchor and gate posts shall be made of intermediate or line posts, or 4" × 4" sawed lumber of a quality equal to the specifications for wood fence posts. Where concrete posts are used, 4" × 4" concrete braces are recommended. 6.5.2.4 Wire Barbed wire and woven wire fencing shall be constructed of a good commercial quality galvanized steel wire. If copper-bearing base metal is used, the copper content shall not be less than 0.2%. Wire for fencing must stand, without sign of fracture, winding tight around wire of the same size; and it shall have a minimum ultimate tensile strength as shown in Table 1-6-7. 1 Table 1-6-7. Wire Tensile Strength Type Tensile Strength (Min) Line Wire No. 7 Gage 2200 lb Line Wire No. 9 Gage 1500 lb Line Wire No. 12-1/2 Gage 700 lb Stay Wire No. 9 Gage 1100 lb 3 4 6.5.2.5 Locks The locks or fastenings at the intersection of the longitudinal and stay wires shall be of such design as will prevent them from slipping either longitudinally or vertically. 6.5.2.6 Fastenings Staples used for fastening the longitudinal wires to wood posts shall be made of No. 9 galvanized steel wire. They shall be 1 inch long for hardwood and 1-1/2 inches long for softwood. Fastenings for concrete and steel posts to be as indicated under specifications for these posts. 6.5.2.7 Galvanizing a. The galvanizing of wire shall consist of a uniform coating of zinc, the weight of which shall be not less than 1.20 oz per sq ft of surface treated. For woven wire, ASTM A116, and for barbed wire, ASTM A121 is to be complied with. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-6-17 Roadway and Ballast b. The weight of coating shall be determined by a stripping test; using the hydrochloric acid-antimony chloride method. Since the density of steel (0.283 lb per cubic inch.) is known, it is only required to determine the diameter of the stripped wire and the ratio of the weight of zinc to the weight of the stripped wire. The sample of galvanized wire may be of any length over 12 inches, but preferably about 24 inches. It shall be cleaned with gasoline or benzine and dried thoroughly, then weighed carefully to 0.01 g. The sample shall then be stripped of the zinc coating by immersing in hydrochloric acid (concentrated HCl with sp gr 1.19) to which has been added antimony chloride solution (made by dissolving 20 g of antimony trioxide Sb O, or 32 g of antimony trichloride SbCl in 1000 cc of hydrochloric acid HCl of sp gr 1.19) in the proportion of 1 cc of the antimony chloride solution to each 100 cc of hydrochloric acid. As soon as the violent chemical action on the wire ceases the wire shall be removed from the acid, washed in water and wiped dry. Its diameter shall then be measured to 0.001 inch by taking the mean of two measurements at right angles to each other. The stripped sample is then weighed to 0.01 g. The original weight (W1) minus the stripped weight (W2) divided by the stripped weight (W2) gives the ratio (r) of the zinc to iron for the sample under test. The weight of coating in ounces per square foot of stripped wire surface is determined by multiplying the constant 163 by the diameter (d) in inches of the stripped wire by the above ratio. This calculation may be expressed by the following formula: Ounces of zinc per square foot of stripped wire surface = 163 dr where: d = diameter in inches of the stripped wire W1 – W2 r = ----------------------W2 6.5.2.8 Manufacture a. In barbed wire the twist shall be uniform throughout and so twisted that the strain shall come equally on all strands. b. The horizontal wires of all woven wire fencing may be provided with tension curves to compensate for expansion and contraction. c. The fencing shall be so fabricated as not to remove any of the galvanizing or impair the tensile strength of the wire. 6.5.3 ERECTION (1991) 6.5.3.1 End, Corner, Anchor and Gate Posts End corner, anchor and gate posts shall be set vertical, at least 3'–4" in the ground, thoroughly tamped, braced and anchored. In long runs of fence, anchor posts shall be spaced not more than 1/4 mile apart. 6.5.3.2 Intermediate or Line Posts Intermediate or line posts shall be set at least 2'–4" in the ground and not more than 16'–6" apart, center to center. The first line post from any corner, anchor or gate post shall be set 10 feet, center to center, from the same. 6.5.3.3 Post Holes a. Holes of full depth shall be provided for all end, corner, anchor, and gate posts, even if blasting must be resorted to. Posts may be installed in drilled holes of the same dimension as the post and the post made firm in place, or they may be installed in larger drilled or dug holes and backfilled and compacted. For intermediate or line post, where rock is encountered, not more than two adjacent wood posts shall be set on © 2010, American Railway Engineering and Maintenance-of-Way Association 1-6-18 AREMA Manual for Railway Engineering Fences sills 6" × 6" × 4' long, braced on both sides by 2'–6" inch braces, 3 feet long. Holes shall be provided for all other posts. Posts shall be set with large end down and in perfect line on the side on which the wire is to be strung. After the fence is erected, the tops of the wood posts shall be sawed off with a 1/4 pitch, the high side being next to the wire and 2 inches above it. b. Backfill of post holes shall be compacted by mechanical means to at least 90% of the ASTM D1557 maximum density at moisture content of within 4% of optimum. An acceptable alternate method of backflll would be the use of a sand-cement slurry consisting of 2 sacks of cement per cubic yard of clean, washed concrete sand and sufficient water to produce a thick slurry. This slurry would be placed in the post holes. 6.5.3.4 Anchoring Wood end, corner, anchor and gate posts shall be anchored by gaining and spiking two cleats to the side of the posts, at right angles to the line of the fence, one at the end bottom, the other just below the surface of the ground. The cleat near the ground surface shall be put on the side next the fence and the bottom cleat shall be put on the opposite side. Intermediate wood posts set in depressions of the ground shall be anchored by gaining two cleats into the side near the bottom of the post, same to be properly spiked. 6.5.3.5 Cleats, Sills, Etc. All cleats shall be 2" × 6" × 2' long. All sills, braces and cleats shall be made of sawed lumber of a quality equal in durability to that of the posts. 6.5.3.6 Bracing End, corner, anchor and gate posts shall be braced by using an intermediate or line post or a 4" × 4" brace gained into the end, corner, anchor or gate post, about 12 inches from the top and into the next intermediate or line post about 12 inches from the ground and be securely fastened. A cable made of a double strand of No. 9 galvanized soft wire looped around the end, corner, anchor or gate post near the ground line, and around the next intermediate or line post about 12 inches from the top, shall be put on and twisted until the top of next intermediate or line post is drawn back about 2 inches. 6.5.3.7 Stretching 1 3 Longitudinal wires shall be stretched uniformly tight and parallel; stays shall be straight, vertical and uniformly spaced. Wires shall be placed on the side of the post away from the track, except that on curves of 1 degree or more the wires shall be placed on the side of the post away from the center of the curve. 4 6.5.3.8 Stapling Staples shall be set diagonally with the grain of the wood and driven home tight. The top wires shall be double stapled. 6.5.3.9 Splicing Approved bolt clamp splice or a wire splice made as follows may be used: The ends of the wires shall be carried 3 inches past the splicing tools and wrapped around both wires backward from the tool for at least five turns, after the tool is removed, the space occupied by it shall be closed by pulling the ends together. 6.5.3.10 Gates a. A hinged metal gate is recommended. © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-6-19 Roadway and Ballast b. The width of farm gates should be not less than 12 feet depending upon the size of agricultural machinery in use in the vicinity, or as required by the laws of the states through which the railway operates. The minimum height of farm gates should be 4'–6" from the surface of the roadway. c. Farm gates should be hinged so as to open away from the track, and, if hinged, swing shut by gravity, and the end of the gate opposite the hinged end should lap by the post a sufficient distance to prevent it from being opened by side pressure. SECTION 6.6 STOCK GUARDS 6.6.1 GENERAL (1991) a. A stock guard should be so constructed as to avoid projecting surfaces liable to be caught by loose or dragging portions of equipment. b. It should be effective against all livestock, have no parts which would catch or hold animals or unnecessarily endanger employees who pass over it in the discharge of their duties. c. It should be reasonable in first cost, durable and easily applied and removed, so as to permit repairs to track at minimum expense. d. It should not rattle during passage of trains. © 2010, American Railway Engineering and Maintenance-of-Way Association 1-6-20 AREMA Manual for Railway Engineering Fences SECTION 6.7 METHODS OF CONTROLLING DRIFTING SNOW 6.7.1 JUSTIFICATION AND SCOPE (1994) a. Although snow fences have been used to protect railways in the U.S. since the 1870’s, the need for passive snow control was diminished by the development of rotary snow plows and more powerful locomotives, and by the increasing frequency of train traffic that helped to keep drifts from blocking tracks. In recent years, however, the need for drift control on railroads has been renewed by technological advances. Remotely controlled switches must be free of snow and ice, and thermal scanners are subject to dysfunction when snow or ice accumulates in the optical path. In addition, the increasing costs of derailments adds incentive for drift protection. b. The methods for preventing or mitigating drifting snow problems discussed here are 1) elevating the road bed above grade, 2) widening cuts to allow the wind to keep tracks blown clear and to provide space for snow to accumulate without encroaching on the tracks, 3) clearing and mowing vegetation along the roadway, 4) placement of bungalows and other structures to prevent the drifts formed by these structures from affecting operations, 5) plowing snow ridges or berms, 6) erecting snow fences, and 7) planting trees and shrubs. 6.7.2 REFERENCES (1994) The guidelines presented here are adapted from the following references, which may be consulted for more detailed information. The References are located at the end of this chapter. 1 • Design Guidelines for the Control of Blowing and Drifting Snow (Reference 14). • Snow Fence Guide (Reference 48). • Drifting Snow (Reference 16). 6.7.3 DEFINITIONS AND TERMINOLOGY (1994) 3 Definitions and terminology are listed here and defined in the Glossary located at the end of this chapter. Bottom Gap Setback Distance, D Effective Fence Height, H Snowfall Water-Equivalent End-Effect Snow Storage Capacity Equilibrium Drift Snow Transport Fetch Snow-Trapping Efficiency Porosity Ratio, P Wind Angle, 4 © 2010, American Railway Engineering and Maintenance-of-Way Association AREMA Manual for Railway Engineering 1-6-21 Roadway and Ballast 6.7.4 SPECIFICATIONS FOR ROADBED GEOMETRY (1994) 6.7.4.1 Elevating Roadbed a. Elevating the roadbed above-grade reduces the accumulation of snow on the track, but does not eliminate snow problems at thermal scanners or other sensitive locations. As a general rule, snow fences are required to protect locations where track is at or above the surrounding terrain. b. Minimum embankment height (He, feet) above grade is given by: H = 0.4S + 2 where: He = measurement from top of ballast S = mean annual snowfall, in feet (Figure 1-6-7). 6.7.4.2 Cut Sections a. Widening cuts allows wind to keep the tracks swept clean of snow. Deeper cuts should also be designed to accumulate snow to reduce the quantity of blowing snow crossing the tracks. In cut sections, the roadbed (bottom of ballast) should be at least 2 feet higher than the bottom of ditch. b. As shown in Figure 1-6-8, minimum horizontal distance, Wtop, from shoulder of roadbed to top of cut is: Wtop = 95 + 5.8H (sin ) where: H = depth of cut measured from roadbed shoulder elevation = the wind angle (Figure 1-6-8) c. Backslopes should be 5:1 or steeper. These guidelines apply to through-cuts and to both windward and leeward sidehill cuts. Although this geometry will prevent drift encroachment on the track, snow fences may still be required to protect sensitive locations such as switches, thermal scanners, and dragging-equipment detectors. Figure 1-6-7. Guidelines for Minimum Height of Roadbed above Grade 6.7.5 SPECIFICATIONS FOR CLEARING AND MOWING VEGETATION (1994) Mowing and brushing operations as normally carried out for fire prevention and other purposes can also reduce snow deposition on the track. Particular attention should be paid to removing or cutting back brush and trees © 2010, American Railway Engineering and Maintenance-of-Way Association 1-6-22 AREMA Manual for Railway Engineering Fences Figure 1-6-8. Recommended Cut Section to Prevent Snowdrift Encroachment within the right-of-way that would otherwise cause drifts to form at critical locations. An option to removing trees is to prune the lower branches to a height of 7 feet. 6.7.6 SPECIFICATIONS FOR PLACEMENT OF BUNGALOWS AND OTHER STRUCTURES (1994) Buildings and other structures on the upwind side of the track can cause drifts that interfere with the operation of switches, thermal scanners, and other equipment. Where prevailing wind directions are well-defined, these problems can be avoided by siting these structures on the downwind side of the track. Where buildings must be placed on the upwind side, they should be located so that the drifts formed around the ends of the building do not encroach on a sensitive area. The drift wings that form around the ends of a rectangular building having width W across the wind, extend laterally to 1.5W on both sides of the building centerline. 1 6.7.7 TEMPORARY CONTROL MEASURES (1994) A common emergency practice in severe winters is to create snow ridges or berms outside of the right-of-way using graders or dozers. Unfortunately, such barriers do not have much storage capacity. A single row of 4-foot snow fence would catch as much snow as fourteen, 2-foot-tall snow ridges spaced 10 feet apart. Snow fences are therefore more effective and less expensive than snow berms. 3 4 © 2010, American Railway Engine
