PIPING DESIGN LAYOUT TRAINING
LESSON 6
UNDERGROUND
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8. UNDERGROUND
8.1
PREFACE
This lesson will cover the procedures required for underground studies. Two things to keep in mind;
first, use Fluor standards as a guide, and second, the guidelines mentioned in this lesson may be
different than jobs you may have worked on in the past. Some clients have their own engineering
standards.
8.1.1
Lesson Objectives
Lessons provide self-directed piping layout training to designers who have basic piping design skills.
Training material can be applied to manual or electronic applications. Lesson objectives are:
•
To know the types of underground systems.
•
To know how to make underground studies avoiding major mistakes and costly changes.
•
To familiarize you with Fluor standards. (Fluor standards are a guide. The standards used on
your contract may differ.)
8.1.2
Lesson Study Plan
Take the time to familiarize yourself with the lesson sections. The following information will be required
to support your self-study:
•
•
Your copy of the Reference Data Book (R.D.B.)
Fluor Technical Practices. The following Technical Practices support this lesson:
000.210.1150
000.210.1160
000.210.1200
000.210.1210
000.210.1211
000.250.2040
If you have layout questions concerning this lesson your immediate supervisor is available to assist
you. If you have general questions about the lesson contact Piping Staff Group.
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8.1.3
Study Aids
Videos on Piping Design Layout Practices supplement your training. It is suggested that you view these
videos prior to starting the layout training. You may check out a copy of the videos from the Knowledge
Centre (Library).
8.1.4
Proficiency Testing
You will be tested on your comprehension of this lesson. Proficiency testing will be scheduled three to
four times a year. Piping Staff will notify you of the upcoming testing schedule.
•
•
•
•
•
Questions are manual fill-in, True-False and short essay (bring a pencil).
The test should take approximately one hour.
You may use your layout training Reference Data Book and material from previous layout training
lessons during the test.
The test facilitator will review your test results with you at a later date.
Test results will be given to Piping Staff.
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8.2
TECHNICAL DUTIES OF LAYOUT PERSON
Develops the following specifications, in accordance with contract requirements and Technical
Practices 000.250.1938 and 000.250.1939.
•
Gravity sewers - design, layout and testing
•
Plant and unit firewater systems. Prepares fire protection system layouts and data and attends
meetings pertaining to it.
•
Advises general piping supervisor as to the need for any additional specifications relating to
underground piping by Civil.
•
Reviews piping material specifications and recommends additions, deletions or changes based on
design requirements. Initiates action for the development of purchase descriptions for any
underground items that are normally not covered in the piping material specifications.
•
Develops and/or directs the development of the underground piping standard details, consistent
with contract and material requirements.
•
Develops and/or directs the development of unit underground layouts and insures they reflect the
job philosophy. Assembles data and calculations relating to the sizing of the unit sewer systems.
•
Maintains underground workbooks: collections of vital data relating to the design of U/G systems.
•
Coordinates underground piping with other groups and establishes a two-way flow of information.
•
Represents general piping in meetings with vendor, clients, engineering and other internal groups.
8.2.1
Underground Systems Work Book
It is the responsibility of the underground layout person to develop and maintain an underground
systems work book that contains:
•
Schedules
•
Narrative underground specifications.
•
Applicable sections of codes having jurisdiction.
•
Piping material information and specifications.
•
Process data (P&ID's, flow conditions, quantities and temperature).
•
Job instructions and design memos relating to underground piping.
•
Calculations and sketches.
•
Notes on interface meetings.
•
Questions and answers.
The above contents are considered minimum and other topics may be added as necessary
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LESSON 6
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8.2.2
Prerequisites to Start Underground Piping Layout and Design
ITEM
1.
2.
3.
4.
5.
6.
7.
Meteorological Data, Rainfall, Frost Depth
Existing Obstructions
Sewer Systems, Segregation
Soil Conditions
Paving
Clients Design Requirements
Federal, State and Local Codes
Additional Information
8. Schedule
*9. Approved Plot Plan(s)
10.00 P&ID's
+11 Preliminary Foundation Design Sketches
12. Process Drainage Rates, Temperatures
and Intermittent or Continuous
13. Piping Materials Specifications
14. Fire System Capacity (in spec.)
15. Site Preparation Drawings
16. Decision on Location of Cooling Water
System (above or below ground)
SOURCE
Basic Jobsite Questionnaire
Client Via Project Manager
Process Engineer
Structural Engineer
Structural Engineer
Project Manager
Project Manager
Piping Supervisor
Piping Supervisor
Piping Supervisor
Structural Engineer
Process Engineer
Piping Materials Engineer
Process Engineer
Structural Engineer
Project
* May not be available at start of layout (use best available info).
+ Discuss approximate size with Structural Engineer.
8.3
UNDERGROUND PIPING MATERIALS
Purpose
The purpose of this guide material is to provide the designer with information relating to some of the
more commonly used underground pipe and fittings.
Scope
The list that follows is for information only and gives the A.S.T.M. or A.W.W.A. specification reference,
size range, and normal use for each type. For additional information the designer should refer to the
specifications or manufacturer's catalogs that are listed. The designer needs to work with the material
engineer for material selection on the project.
Selection of Pipe
Selection of pipe for underground service depends upon pressure, temperature, commodity, durability,
cost, availability, and client requirements.
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8.3.1
Vitrified Clay Pipe
Vitrified clay pipe (standard and extra strength, A.S.T.M. C-700) is used for gravity piping
handling surface drainage and process drainage when this piping is not under concrete paving
or buildings. It is also used for sanitary sewage to within 5 feet of an outside wall of a building
where there is no paving and for acid sewers with acid proof cement joints.
It is available in extra strength in the following sizes: 4"-6"-8"-10"-12"-15"-18"-21"-24"-27"-30"33"- 36". Joint lengths vary per manufacturer, but are approx. in 2' or 3' lengths in sizes up to
12" and 3' to 5' lengths in sizes 15" through 36". (Catalogs: Cantex, Interpace)
8.3.2 Cast Iron Soil Pipe
Cast iron soil pipe (A.S.T.M. A-74) is used for gravity piping handling surface drainage, process
drainage or sanitary sewage under concrete paving or buildings. It is available in 2"-3"-4"-5"-6"8"-10" -12"-15" sizes. Joint lengths available in 5' & 10' lengths. (Catalogues: Tyler, CalAlabama, Rich Manufacturing).
8.3.3
Cast Iron Water or Pressure Pipe
Cast iron water pipe (A.W.W.A. C-106, 108 & 110) is used for pressure or sewer systems where
long runs with few branches are required. Pipe & A.W.W.A. fittings are available in sizes 2"
through 48". Joint lengths vary from 12' to 18' depending upon the manufacturer. (Catalogs:
U.S. Pipe, Mead Pipe.)
8.3.4
Asbestos Cement Pipe (Transite Pipe) (Reference only no longer used)
Asbestos cement pipe (A.W.W.A. C-400) in conjunction with cast iron fittings was used for
pressurized water service. It had the advantage of lower installed cost than most other piping
materials, but would not be used in congested areas where it is susceptible to damage.
Available sizes were 4"-6"-8"-10"-12"-14"-16"-18"-20"-24"-30"-36" in pressure classes 100, 150
and 200. (Catalogs: Johns-Mansville, Certain-teed.)
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FIGURE 8-1
FIGURE 8-2
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8.4
DESIGN CONSIDERATIONS
8.4.1
Settlement
The following list identifies problems created by differential settlement together with
recommended solutions. The degree of the problem should be determined by discussions with
the Structural Engineer and a review of the soil report.
Sewer lines connected to manholes -- differential settling of the manhole and the sewer sometimes
breaks the sewer pipe. A pipe joint just outside the manhole lessens this danger. If the soil conditions
are unstable or a high water table could leach sand bedding out from under the pipe a second joint
within three feet of the first should be provided. In these situations cast iron pipe should be used in
place of vitrified clay pipe. The joints must be flexible such as a compression joint, mechanical joint, or
even a lead joint is considered flexible.
Differential settlement involving cooling water branch lines between large cooling water headers, which
could settle and exchangers on piled foundation which may not, could over stress the piping. This
problem can be remedied by locating the headers so that the branch lines are at least 10 feet long and
providing flexible connectors (Dresser, Smith-Blair, etc.) at either end of the branch for steel pipe, or by
using mechanical joints for cast iron pipe.
For other types of settlement problems these methods just described should provide a remedy.
Unstable bedding -- when the bottom of the trench is not sufficiently stable or firm, to prevent vertical or
lateral displacement of the pipe after installation a non-yielding foundation must be designed.
8.4.2
Crushed rock
The simplest supplementary foundation is to excavate native soil below grade of bedding material and
replace with a layer of broken stone, crushed rock, or other coarse aggregate that may produce the
desired stability under conditions where the instability is only slight.
8.4.3
Encasement
Under conditions where an extremely unstable area is to be crossed, and that area represents a very
short length of line, it is possible to reinforce the pipe by full concrete encasement and adequate
reinforcing steel to produce a rigid beam.
8.4.4
Piling
In some instances, lines must be constructed for considerable distances in areas generally subject to
subsidence, and consideration should be given to constructing them on a timber platform or reinforced
concrete cradle supported by piping. Supports should be adequate to sustain the weight of the full
sewer and backfill.
The details and requirements for the above should be worked out in conjunction with the Structural
Engineer based on the recommendations of the soil report.
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8.4.5
Angle of Repose
Underground lines installed below adjacent foundations should not undermine the 45o angle of repose
of the foundation (See Figure # 8-3). Where there is no obvious solution consult with the Structural
Engineer to see if the actual conditions permit a steeper angle. It may also be possible to brace the
trench if equipment has been set, and to protect the pipe against loads by encasement.
FIGURE # 8-3
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8.4.6
Breakage
Precautions must be taken to prevent breakage of pipe due to construction and maintenance
equipment traffic.
Depth of cover for protection against surface loads is covered in another section.
Guard posts are provided to protect the above ground features of the firewater system.
Cleanouts in vitrified clay systems are subject to breakage, particularly in offsite areas. Where
cleanouts are thus exposed, protective structures similar to those for the firewater system, as well as
concrete cradles, must be detailed. Notes on offsite drawings should state, "INSTALLATION OF
CLEANOUTS SHOULD NOT BE COMPLETED UNTIL PROTECTION SHOWN ON DETAIL
DRAWING CAN BE PROVIDED".
Use Cast Iron adjacent to manhole to avoid breakage caused by differential settlement of loss of
bedding in high water table (See Figure #8-4).
FIGURE # 8-4
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8.4.7
Stub-Ups
Stub-ups are used to connect underground lines carrying water, steam, air process liquids and the like
with above ground facilities. Flanged and welded underground lines should terminate 18 inches above
high point finish surface with a flame cut end. The above ground spool should indicate bevel end or
face of flange at 12" above H.P.F.S. (See Figure #8-5). This will permit field fit-up.
Cathodic protection may be required depending on the soil conditions.
FIGURE # 8-5
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8.5
SYSTEM SAFETY CONSIDERATIONS
8.5.1 Purpose of Seals
Seals play a vital role in maintaining safe operation of a process plant sewer system. Under
normal conditions, sewers are only partially filled because flow rates are designed for storm or
firewater quantities. The large vapor spaces in process plant sewers will frequently contain
flammable vapors. Liquid seals form vapor barriers and prevent flame fronts or explosions from
running the full length of the sewer system. Without a sealed sewer system, a fire in one area
could ignite vapors in a catch basin, which could flash through the sewer to initiate a fire at
some other location.
Seals also prevent the release of vapors or gases to the atmosphere at grade level where they
could create a hazard or contribute fuel to a fire.
8.5.2
Location of Seals
Catch Basins
Catch basins discharging to any sewers that have the possibility of containing flammable or
hydrocarbon vapors are isolated from the lateral by one of the following:
(a) Providing an outlet seal at the line where it leaves the catch basin (See Figure # 8-6a).
(b) Routing the outlet line to a manhole or adjacent catch basin and providing an inlet seal at
the point of entry (Figure # 8-6b).
Manholes
Laterals leaving a unit are isolated from main or trunk sewers by providing manholes at junction points
and routing the lateral into the manhole at a sealed inlet (Figure # 8-6b).
The plant main sewer may be sectionalized by providing sealed inlets at those manholes that would
enable isolation of major process area groups, storage areas, treatment areas, marine terminals, etc.
Baffle type manholes serve this purpose on larger sewer runs (Figure # 8-6c).
Drains and Funnels
Groups of drain funnels in fairly close proximity, say up to 30' apart, are connected to a single branch
line which is isolated from the rest of the system by running it to a catch basin or manhole and providing
an inlet seal at the point of entry.
Generally funnels serving pumps are isolated from the other funnels on the branch by providing a
running trap between the pump funnels (Figure # 8-6d).
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Where a sewer system must handle toxic or extremely hazardous material, each funnel is provided with
a "P" trap type seal (See Fig # 8-6e), and the branch line is connected to the lateral at an inlet sealed
manhole.
Where a funnel is located close, say within 10' of the catch basin it is connected to, an inlet seal is not
required, since a fire can travel above ground as easily as through the sewer.
8.5.3
Types of Seals
FIGURE # 8-6
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8.5.4
Venting
Sewers in general are designed for gravity flow. In a sealed system (i.e. without vents), a rise in water
level would reduce the vapor space and cause an increase in pressure. This would reduce the design
capacity of the sewer. Therefore vents are necessary to prevent vapor lock and to release vapors to a
safe location.
Vents serve to prevent rapid pressure buildup in the sewer should hot commodities or water enter the
sewer and vaporize any liquid hydrocarbons present.
8.5.5 Location of Vents
Vents are provided at every manhole where the inlet line is liquid sealed so as to prevent venting to the
next upstream manhole.
The highest manhole in a system is provided with a vent.
Both chambers of a baffle sealed manhole are provided with vents.
See the design specification for additional information.
8.6
ON-SITE UNDERGROUND LAYOUT
The purpose of this guide material is to provide the layout designer with instructions and a standardized
approach to the layout of the Underground Piping Systems within a unit.
Scope
This instruction covers the step by step development of the underground systems layout and points out
critical items with respect to the design.
General
Specifications covering the layout and design of sewer and firewater systems are normally prepared for
each contract. These specifications must be carefully followed as they provide the basis for design.
8.6.1 Drainage Areas
In process or operating areas, the distance a liquid spill must travel across the pavement to a catch
basin should be kept to a minimum. Concrete paved areas are subdivide into drainage areas, normally
3600 sq. ft. (See contract specifications.) Each drainage area is bounded by a high perimeter and
drains to a catch basin located at a low point. Figure 8-7.
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See Figure 8-7.
8.6.2
Drainage Area Sizing Guide
Figure #8-8 may be used as a guide to make a quick evaluation of the minimum and maximum
drainage area sizes and catch basin locations based on maintaining required paving slopes at various
drops in paving from high to low point.
Drainage areas are based on two considerations: The elevation difference between high and low
points, and the prevention of fire flow and process spills flowing between adjacent areas. Ideally, a
drainage area should be about 50 to 60 feet square, draining to a catch basin at or near the center.
Equipment requiring curbed areas shall be noted on the P&ID's or defined in the job specifications.
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FIGURE # 8-8
8.6.3
Guidelines
Locate the high point of paving:
at perimeter of concrete paving or edge of road.
at edge of buildings
along major access ways around heater areas, to direct spillage
away from heater and other equipment.
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When locating catch basins give consideration to the following:
•
locate near center of drainage area if possible.
•
do not locate under equipment or piping manifolds.
•
do not locate at building entrances or ladder and stairway landings.
•
keep at least five feet clear of equipment work areas, such as alongside of pumps.
8.6.4
Preliminary Work
In order to avoid design and construction problems resulting from interferences the following items are
shown on the layout.
•
Existing concrete obstructions (foundations, sumps, etc.).
•
Existing underground electrical ducts and piping systems.
Foundations of columns, heaters, pumps, structures and pipe supports should be indicated based on
whatever information the Structural Engineer can provide (or your best guess). Foundation depths and
thickness have an important bearing on the routing of underground piping (structural engineering. will
advise).
8.6.5
Paving and Surface Drainage
Perimeter of concrete paving to encompass all equipment within unit area. Paving perimeter is
normally five feet beyond the furthest projecting equipment. In the interest of economy this outer limit
may be staggered to suit groups of equipment which do not project as far. (Keeping the jogs to a
minimum.) Drainage outside the perimeter of the concrete paving is by Civil.
NOTE:
Job specifications may dictate that certain equipment groups handling gases or liquids
that vaporize at ambient temperatures may not require concrete paving.
Types and characteristics of paving (verify with your Civil/Structural Eng.)
•
•
•
•
•
•
Concrete, 6" thick
Concrete, 4" thick
Asphalt, 3" thick
Asphalt, 2" thick
Crushed rock 3" deep
Concrete sidewalks - 4" thick 3'-
Paving slope -
Minimum 1/8"/ft.
Maximum 1/2"/ft.
Process liquid spills truck traffic.
Process liquid spills, no truck traffic.
Primary roads.
Secondary roads, general paving and parking areas.
General area cover.
0" wide, raised 1" above adjacent finished surface.
Verify with your Civil/Structural engineer
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8.6.6
Types of Catch Basins
Figure 8-9 illustrates four basic types of catch basins and drain boxes.
•
Concrete box per job standards, precast or poured-in-place are used as area drains and seal
boxes in combined sewer (storm and process water). Liquid level in box should be at or
below frost line.
•
Concrete pipe may be used for perimeter areas where only a single outlet is required.
•
Dry box type catch basins, are used as area drains for heater drainage areas in order to
remove all hydrocarbon liquids from the area promptly in event of a tube break. Do not locate
dry boxes under burners. The downstream end of the dry box outlet line shall be kept
separate from other heaters or equipment areas and sealed in a catch basin or manhole.
(Generally located 50' or more from the shell of the fired equip.)
•
Cast Iron - [Not shown] used as area drain only generally in separate storm sewer. Not used
in cold climates where they could be subject to freezing. Not used in crushed rock areas.
Figure 8-9
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8.6.7 Drawings
Process area underground layouts are normally done on a brownline of the plot plan at a scale of 1" =
20' or 1" = 10'. The initial layout is in the form of a transposition with sufficient information shown to
enable a reasonably accurate material takeoff. The final layout and design is handled as a part of the
development of the underground piping drawings. Figure 8-10 shows a portion of an underground plan
drawing.
Figure 8-10
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8.6.8
Sewer System Piping
The unit collection headers for storm, process or combined sewers (laterals) are usually located under
the pipeway area for convenience in connecting catch basins and drain funnels on both sides of
pipeway. If the electrical power duct system is also located in this area, the layout designers from both
groups should work closely to establish easements. Laterals are installed below frost line.
Normally the slope of the longest path governs the inverts in the system and the depth of the sewer at
the start, or high end.
Sewer laterals leaving process units are sealed at manholes on the plant sewer mains. Sealing and
venting philosophy for sewers containing hydrocarbon or flammable vapors is shown on Fig. 8.6a and
Fig. 8-6b, and in the section on Manholes in this document.
Sublaterals are routed from the catch basins and/or branches to the laterals. The connection at the
lateral may be at a WYE branch or at a manhole. In a sewer collecting process drainage, manholes
may be located along the lateral to serve as seal boxes for the incoming branches.
Pump and equipment process drains discharge into drain funnels. A 6" minimum size opening for all
drain funnels is preferred. Where a 6" opening does not provide sufficient area to accommodate
multiple drains a larger opening is provided.
Drain funnel requirements are indicated on the P&ID's. Approximate locations are shown on the initial
layout. Exact locations are set later by the above ground piping layout. Groups of funnels in fairly
close proximity, say 30' apart, are connected to a single branch line which is run to a catch basin,
manhole or seal box.
Each drain, sublateral or lateral shall be accessible for rodding out by providing either a cleanout or
catch basin at its upper terminus.
Limitations for the use of cleanouts are defined in the job specifications.
Indicate line class, size, and slope for laterals, sublaterals, and branches. Indicate invert elevation for
start and termination of unit lateral. Use line sizing criteria provided in conjunction with Sewer Sizing
Chart, or job specification.
NOTE:
It will be necessary for the Layout Designer to consult with the Process Engineer to determine the
source, nature and quantity of each process waste stream discharging to the sewer. A permanent
record of this information should be maintained for future reference.
To facilitate construction, maintain a constant slope over long runs, change line sizes as required, and
maintain common invert elevations for adjacent parallel lines.
Sanitary sewers within buildings are designed by the Plumbing Section of the Architectural Group to a
point five (5) feet outside of the building, at this point you will be given the design information, e.g.,
fixture units being served, gpm and velocity. Sanitary sewer minimum size is 4". Minimum slope to be
1/8" per foot.
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8.6.9
Manhole and Catchbasin Piping Elevations
Use Figure # 8-11 and the formulas that follow to calculate and set the elevations of manholes and
catchbasins.
FIGURE # 8-11
Where:
x=
horizontal distance from inside face of wall to intersection of invert (or B.O.P.)
lines at 22½o bend. (feet)
y=
difference in invert (or B.O.P.) elevations between points 2 and 3.
w=
sum of:
=
=
=
difference in inlet and outlet line size (D2-D1) (feet)
minimum liquid seal = .5 feet
D1 x cos 22.5o
(W is tabulated in Table 1 & 2., for lines at 22½o only.)
s=
slope of inlet line (feet/foot)
E=
inside diameter or inside face to face of walls for manhole or
catch basin (feet)
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Procedure
Calculate invert elevation (or B.O.P. for steel pipe fabrication) at point 1 or 1a.
Deduct "W" which yields invert elevation (or B.O.P.) of seal pipe at point 2.
Calculate X and Y using equations 1 and 2 that yield invert (or BOP) and location of point 3.
When seal pipe enters box at an angle other than 22.5o use the natural tangent of that angle in
place of 0.4142 in equations 1 and 2.
Dimension "W" must be calculated in the above situation using D1 x cos of the angle used, for
dimension (c).
Dimension "W" is the sum of (b), (c), and (d) when inlet line is a branch run at a higher elevation
than the normal flow line of the system.
DO NOT USE THESE TABLES IF THE LINE ENTERS AT AN ANGLE OTHER THAN 22.5o.
TABLE 1
4"
6"
8"
10"
12"
14"
15"
16"
18"
20"
24"
4"
0.81
DIMENSION "W" (FEET)
BASED ON INVERT EL. FOR C.I. OR CLAY PIPE
OUTLET PIPE SIZE
6"
8"
10"
12"
14"
15"
0.97
1.14
1.31
1.47
1.64
1.72
0.96
1.13
1.30
1.46
1.63
1.71
1.12
1.28
1.45
1.61
1.70
1.27
1.44
1.60
1.69
1.42
1.59
1.67
1.58
1.66
1.65
16"
1.81
1.78
1.78
1.77
1.76
1.74
1.74
1.73
18"
1.97
1.95
1.95
1.94
1.92
1.91
1.90
1.90
1.89
20"
2.14
2.13
2.12
2.10
2.09
2.08
2.07
2.06
2.05
2.04
18"
1.97
1.96
1.95
1.93
1.92
1.91
1.90
1.89
20"
2.14
2.12
2.11
2.10
2.09
2.08
2.07
2.05
2.04
24"
2.47
2.46
2.45
2.43
2.42
2.41
2.40
2.39
2.37
2.35
TABLE 2
4"
6"
8"
10"
12"
14"
16"
18"
20"
24"
4"
0.85
6"
1.02
1.01
DIMENSION "W" (FEET)
BASED ON B.O.P. FOR STEEL PIPE
OUTLET PIPE SIZE
8"
10"
12"
14"
16"
1.19
1.37
1.53
1.64
1.80
1.18
1.35
1.52
1.62
1.79
1.16
1.34
1.51
1.61
1.78
1.33
1.49
1.60
1.76
1.48
1.59
1.75
1.58
1.74
1.73
24"
2.47
2.46
2.45
2.44
2.42
2.41
2.40
2.40
2.39
2.37
2.35
PIPING DESIGN LAYOUT TRAINING
LESSON 6
UNDERGROUND
Page 22 of 25
15/30/2002 REV 0
8.6.10 Sewer Sizing Guide
•
Purpose
The intent of this instruction is to provide the designer with an organized approach to sizing
sewer lines, and to promote a better understanding of the hydraulics involved in sewer design.
•
Design Basis
The general requirements for the plant sewer systems are outlined in the design specification. Line
sizing is based on the expected flows in the line plus a safety factor for storm water flows. The
design specification should provide the following:
•
Rainfall intensity (inches/hour)
•
Maximum fire water flow based on pumping capacity, and fire protection facilities. (spray
systems, monitors, etc.)
•
Definition of waste water system.
8.6.11 Sewer Layout
The Civil Group is responsible for the sewer system layout.
•
Generally inverts for the mains can be set by determining which "path" is the longest. However
this must be analyzed since shorter paths at steeper slopes may govern.
•
On a large plant several trial designs may be required to determine the most advantageous
routing.
8.6.12 Sewer Sizing Calculation Sheet
The Sewer Sizing Calculation Sheet may be utilized to provide a permanent record of the hydraulic
design of the principal sewer systems. It is used during the layout and design phase to keep track of
calculations.
The intent is to use the form for unit laterals, sublaterals and branches. (See design specification for
definitions)
Using the chart is actually a "step by step" automatic way to size the system. The notes that follow
serve as instructions.
SEWER SIZING CALCULATION SHEET
Line No.
_________________________
Layout Dwg No. ______________________
System No. __________________________
1
FROM
MK.
2
TO
MK.
3
SQ. FT.
PAVED
4
5
SQ. FT.
STORM
UNPAVED RUNOFF
6
7
STORM PROCESS
RUNOFF DRANAGE
(GPM)
(GPM)
INCREMENT
TOTAL
(GPM)
8
FIRE
WATER
(GPM)
Contract No.
9
DESIGN
FLOW
10
SEWER
DIA.
(IN.)
(IN.)
______________________
11
12
VELOSITY SLOPE
(FT./SEC.) (FT./FT.)
6+7 or 7+8
NOTES:
1.
2.
3.
4.
z
STORM RUNOFF BASED ON THE RAINFALL INTENITY OF ______"/HOUR
FACTOR OF IMPERVIOUSNESS FOR UNPAVED AREAS = _______
FIREWATER FLOW IS BASED ON ________GPM PER CATCH BASIN
LINE SIZE CHANGES ALONG A RUN SHOULD BE REFLECTED - COLUMN 14 BY AN APPROXIMATE INCREASE IN THE INVERT DROP
13
LENGTH
(FT.)
14
INVERT
DROP
(12X13)
15
I.E.
UPPER
(FT.)
16
I.E.
LOWER
(FT.)
17
18
ELEV.
APPROX.
GROUND COVER
UPPER
17-(15+10)
PIPING DESIGN LAYOUT TRAINING
LESSON 6
UNDERGROUND
Page 23 of 25
15/30/2002 REV 0
Using the Sewer Sizing Calculation Sheet
•
On a copy of the sewer layout, assign identifying letters to each junction where flow is
increased, breaking the sewer into individual segments or runs to be separately sized on the
chart.
•
Column 1: List the identifying letter for the upstream end of the first run. (The first line
should be used for the first run in the system.)
•
Column 2: List the identifying letter at the downstream end of the same run.
•
Column 3: Enter the square footage of the paved area with runoff to the junction point
designated in column 1 of the same line.
•
Column 4: Enter the square footage of unpaved areas.
•
Column 5: Calculate and list the storm runoff based on areas listed in columns 3 and 4,
using appropriate formulas in the design specification.
•
Column 6: List the total cumulative runoff for run by adding runoff in column 5 to that listed in
column 6, in the preceding line.
•
Column 7: List the total cumulative process drainage to the point listed in column 1.
•
Column 8: List the total cumulative firewater flow, based on requirements in the design
specification.
•
Column 9: List the design flow, the total of columns 6 + 7 or 7 + 8 whichever is greater.
•
Column 10, 11 and 12: Select and enter the pipe size, flow velocity and line slope
respectively, using the Pipe Flow Chart in 000.210.1160, Attachment 2, in the Piping
Engineering Design Guide, Vol. 2. In the larger sizes there is a range in choices for any
given flow. Selections are a matter of judgement, but consider the following:
;
Velocities of 3 to 4 ft. per sec. are preferred.
;
Use lesser slopes where limited by elevations at the terminus of the system, or
where excavation is difficult and/or excessive.
;
Use steeper slopes where terrain gradient permits.
•
Column 13: Enter the length of run in feet and decimals of a foot between the points
designated in columns 1 and 2. (For example: 242.25').
•
Column 14: Multiply col. 12 x col. 13 to calculate the invert drop in decimals of a foot, and
enter the result. If there is a size change in the run, add half the difference in nom. pipe
size.
PIPING DESIGN LAYOUT TRAINING
LESSON 6
UNDERGROUND
Page 24 of 25
15/30/2002 REV 0
•
Column 15: The highest invert elevation at the start of a system should be based on
the cover requirements and length of the branches serving the junction point listed. In
subsequent runs if the line size is larger than in the preceding section, the invert
should drop accordingly.
•
Column 16: The lowest invert elevation, at the end of the system. Calculate by
deducting the value in column 14 from that in column 15.
•
Column 17 and 18: Self-explanatory, used for reference only.
Remember to add the required information in notes: 1, 2 & 3.
8.6.13 Utility Water Systems
Cooling water supply and return headers, if underground, are routed approximately five (5) to ten (10)
feet from the exchanger channel end connections to keep branches short yet still permit for some
adjustment. If there is a choice it is preferable to keep the main headers out from under concrete
paved areas.
Where frost is not a factor the trench depth for the cooling water headers should be kept to a minimum.
As a general rule 3'-0" cover is adequate protection for truck loading for steel lines 24" and smaller in
unpaved areas. Greater cover may be required for larger sizes and/or other piping materials. Under
concrete paving one (1) foot cover may be adequate. (See Civil/Structural Eng.)
Branch lines from the cooling water headers to the exchangers are taken off the bottom quadrant of the
header if clearance above will not permit adequate cover. Short branch piping may be routed in the
frost zone and supply and return need not be at the same B.O.P.
Provide a minimum clearance of eighteen (18) inches between cooling water supply and return headers
(24" for lines 30" and larger) to prevent heat transfer.
Utility water headers are located under the pipeway area in order to keep branches to the utility stations
at pipe support columns short.
Potable water piping within buildings is designed by the Plumbing Section of the Architectural Group to
a point five (5) feet outside of the building.
If practical the potable water header and sewer laterals and/or mains shall not be less than ten (10) feet
apart horizontally. If the requirement cannot be met, the water header shall be placed on a solid shelf
and at all points shall be at least twelve (12) inches above the top of the sewer line at it's highest point.
Locate unit block valves at plot limits. Protect from maintenance vehicles with guard posts.
In freezing climates all utility water headers shall have their top of pipe at or below the frost line.
(Firewater shall be 1'-0" below frostline.)
PIPING DESIGN LAYOUT TRAINING
LESSON 6
UNDERGROUND
Page 25 of 25
15/30/2002 REV 0
8.6.14 Firewater System
Hydrants are located along plant roads or unit perimeters, so that a fire at any location in the process
unit can be approached from two directions by men handling fire hoses connected to the hydrants.
The hose coverage area is based on a nozzle with a 1 1/8" tip connected to 250 feet of hose. A
brownline of the plot plan should be marked-up to show monitor and hydrant locations as well as their
coverage arcs. The Fire Protection Engineer, a plant Fire Marshall, and local Fire Authorities review
this document. (Several onionskin circles with 250' radius positioned on the plot can assist in
determining the best hydrant locations.)
Hydrants or monitors should not be located where they will conflict with exchanger tube pull or other
maintenance activities. Hydrants or monitor locations that might interfere with construction erection
activities should be noted to "install after equipment has been erected."
Monitors and hose reels are located to protect specific hazards as outlined in the job specifications.
Water spray systems, when required are designed in accordance with the National Fire Specification,
N.F.P.A. #15. Stub and valve location is also covered by this standard.
This copy is intended for use solely with
Piping Design Layout Training.
For other purposes, refer to the original document
available through Knowledge Online.
Practice 670 210 1150
Publication Date 20Sep95
Page 1 of 21
FLUOR DANIEL
STORM DRAINAGE
PURPOSE
This practice provides guidelines for overall storm drainage design for a project site and
applies to projects being performed by the Civil Discipline that require storm drainage
design.
Information contained herein should be used by the Civil Engineer as a guide. Many design
criteria, data, charts are available in text books, handbooks, manuals, but some of them are
shown here. The Design Engineer should stay up to date on materials, specifications, and
design criteria.
Each project will have its own set of situations to be analyzed and addressed with the best
engineering concept. Good engineering judgment and most economical solutions should be
utilized.
For complicated projects, obtain appropriate reference publication and design storm drainage
system as specified in the publication. For very large projects, computer programs are
available where time and cost saving is justified. Even for smaller systems, simple computer
programs are available which provide quick and accurate results.
SCOPE
This practice utilizes many design criteria, data, charts, textbooks, handbooks, and manuals
available for storm drainage design.
This practice contains types of commonly used hydrology analysis, hydrology design criteria,
the rational method to determine storm water runoff from a drainage area, hydraulic design
of open channel and closed storm sewers, storage basins, and design of culverts.
APPLICATION
Each engineer or designer performing storm drainage design should utilize this guideline on
each project. It is the overall responsibility of the Lead Engineer to ensure that this practice
is used for storm drainage design on projects.
GENERAL
CONSIDERATIONS
Comprehensive storm drainage design includes more than determination of runoff quantities
and the layout of a collection or conveyance system to dispose of the runoff. Integral to the
design is the consideration of erosion control and its impact on adjacent properties. The
design of the storm drainage system should be prepared in conjunction with the grading
design since the grading directly influences the type and design of drainage system
employed. It is necessary that the drainage philosophy be established before the grading
design is prepared.
The impact of increased/decreased runoff from the project site to adjacent properties must be
considered. Further development within the watershed must also be considered. Stormwater
management is integral to the drainage system design. It is becoming more commonplace
Civil Engineering
This copy is intended for use solely with
Piping Design Layout Training.
For other purposes, refer to the original document
available through Knowledge Online.
Practice 670 210 1150
Publication Date 20Sep95
Page 2 of 21
FLUOR DANIEL
STORM DRAINAGE
for local/state authorities to require stormwater management programs in the form of
retention/detention ponds. The rate of runoff is frequently controlled by statute.
Implementation Of
Storm Drainage
Practice
Implementation of storm drainage practice includes the following:
Data collection
Define existing watershed
Define/develop drainage philosophy for site
Develop proposed layout of system
Prepare calculations for system
Design stormwater management facilities, if required
Data Collection
Review local/state statutes.
- Erosion Control
-
Stormwater Management
Establish/determine requirements for permit applications.
- Plan Requirements
-
Calculations
Obtain most recent topographic plans of watershed.
- Use USGS to establish general location and define total watershed.
-
Use city/county topographic plans for preliminary design in absence of more
accurate data.
-
Obtain topographic survey prepared at suitable accuracy for final design.
Obtain rainfall data.
- Obtain latest rainfall data from appropriate governmental agency (weather bureau).
Define Existing
Watershed
Delineate watersheds on topographic plans.
Calculate existing runoff (Q10, Q25, Q50, and Q100) as required.
- Onto site
-
From site
Define/Develop
Design Philosophy
For Site
Consider method of collecting runoff.
- Sheet flow versus series of drainage inlets
-
Ditches versus underground piping system
Civil Engineering
This copy is intended for use solely with
Piping Design Layout Training.
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available through Knowledge Online.
Practice 670 210 1150
Publication Date 20Sep95
Page 3 of 21
FLUOR DANIEL
STORM DRAINAGE
Establish design criteria.
Develop Proposed
Layout Of System
Prepare conceptual grading and drainage plan.
Delineate drainage area for each inlet or section of ditch.
Note!!! For conceptual design, space inlets based on 1 inlet per 10,000 sf.
Prepare Calculations
For System
Design collection system for design storm frequency.
Refine grading plans and adjust layout of storm drainage.
- Check ponding at inlets. Check capacity of grates.
-
Consider special inlets with high capacity grates.
-
Check ditch flow for depth and velocity. Consider need for erosion netting, sod, or
rip rap/energy dissipaters. Use available charts for design of open channels.
-
Check pipe flow for cleansing/scouring velocity and depth of flow.
-
Determine inlet and outlet losses for manholes and culverts.
Pay special attention to details for proper drainage at the following:
- Intersections of roadways
-
Truck docks
-
Building entrances
-
Rail docks/yards
-
Pedestrian crossings
-
Roof drainage discharge points
-
Parking lots
Design Stormwater
Management Facilities
Code search
- Check state/local/federal requirements.
Prepare calculations/drawings for the following:
- Erosion control
-
Retention/detention basins
-
Outflow structures
-
Emergency spillways
-
Earth dams
Civil Engineering
This copy is intended for use solely with
Piping Design Layout Training.
For other purposes, refer to the original document
available through Knowledge Online.
FLUOR DANIEL
Practice 670 210 1150
Publication Date 20Sep95
Page 4 of 21
STORM DRAINAGE
HYDROLOGY
ANALYSIS
Technical Release 55
(TR-55)
Technical Release 55, Urban Hydrology for Small Watersheds, presents simplified
procedures to calculate storm runoff volume, peak rate of discharge, hydrographs, and
storage volumes required for floodwater reservoirs. These procedures are applicable in small
watersheds, especially urbanizing watersheds, in the United States.
The model described in TR-55 begins with a rainfall amount uniformly imposed on the
watershed over a specified time distribution. Mass rainfall is converted to mass runoff by
using a runoff CN (curve number). CN is based on soils, plant cover, amount of impervious
areas, interception, and surface storage. Runoff is then transformed into a hydrograph by
using unit hydrograph theory and routing procedures that depend on runoff travel time
through segments of the watershed.
Use peak discharge method for up to 2,000 acres of drainage area. Use tabular method for
up to 20 square miles of drainage area.
In TR-20, the use of TC (Time of Concentration) permits this method for any size watershed
within the scope of the curves or tables, while in TR-55, the procedure is limited to a
homogeneous watershed. The approximate storage routing curves are generalizations
derived from TR-20 routings.
Use TR-20 if the watershed is very complex or a higher degree of accuracy is required.
Use TR-20 if TT (travel time) is greater than 3 hours and time of concentration TC is greater
than 2 hours and a drainage area of individual subareas differ by a factor of 5 or more.
Refer to Civil Engineering software, quick TR-55, and TR-20 for computer application.
Synthetic Unit
Hydrograph Method
(Chapter 16, Pages
16-1 To 16-26)
Over the past 2 decades, the federal, state, county, and local agencies have made numerous
hydrologic investigations of drainage basins using synthetic unit hydrograph methodology.
The synthetic unit hydrograph method should be used on larger drainage areas.
Rational Method
The rational method is 1 of the most widely used techniques for estimating peak runoffs, and
is applicable to most of the drainage problems encountered on Fluor Daniel projects.
The rational formula is Q = CIA
where
Q
=
Peak runoff, cfs
C
=
Coefficient of runoff, the rate of direct runoff to rainfall
Civil Engineering
This copy is intended for use solely with
Piping Design Layout Training.
For other purposes, refer to the original document
available through Knowledge Online.
FLUOR DANIEL
Practice 670 210 1150
Publication Date 20Sep95
Page 5 of 21
STORM DRAINAGE
I
=
Rainfall intensity, inches per hour, corresponding to the time of
concentration
A
=
Tributary area, acres
The rational method is commonly used for determining peak discharge from relatively small
drainage areas up to 200 acres.
HYDROLOGY
DESIGN CRITERIA
Normally, design for a storm frequency of 10 years for projects, unless otherwise specified by
the client.
Check for storm frequency of 50 years to estimate the consequences of flooding the site.
For major structures such as culvert under public highway, use a storm frequency of 50
years.
Design major flood control channels and major lift stations for a storm frequency of 100
years.
Stormwater runoff from tank farms is normally not included in the design. Stormwater is
impounded within the dikes and released after the peak stormwater runoff has passed.
Design containment storage within containment areas for a storm frequency of 10 years,
24-hour storm for projects, unless otherwise specified by the client.
Ponding at inlets should be less than 3 inches for a frequency of 25 years storm.
RATIONAL
METHOD
Rational Formula
The rational formula is Q = CIA. On a topographic plan of the drainage area, draw the
drainage system and block off the subareas draining into the system.
Determine A, the area of each subarea in acres.
Coefficient Of Runoff
The coefficient of runoff is intended to account for the many factors which influence peak
flow rate. The coefficient of runoff primarily depends on the rainfall intensity, soil type and
cover, percentage of impervious area, and antecedent moisture condition.
Determine the coefficient of runoff C, for appropriate class of ground surface from the
following table. If more than 1 class of ground surfaces fall in 1 tributary drainage area, use
a composite coefficient of runoff value.
Civil Engineering
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For other purposes, refer to the original document
available through Knowledge Online.
Practice 670 210 1150
Publication Date 20Sep95
Page 6 of 21
FLUOR DANIEL
STORM DRAINAGE
Coefficient of Runoff
C
Roofs
Pavements
Concrete
Asphalt
Oiled Compacted Soil
Compacted Gravel
Compacted Impervious Soil
Natural Bare Soil
Uncompacted Gravel
Compacted Sand Soil
Natural Soil, Grass Cover
Uncompacted Soil
Lawns
1.00
1.00
1.00
0.80
0.70
0.60
0.60
0.50
0.40
0.40
0.20
0.20
Composite coefficient of runoff C:
A1C1 + A2C2 + A3C3 + −−−−AnCn
A1 + A2 + A3 + An
where
A1 A2 A3 ---- An
C1 C2 C3 ---- Cn
=
=
Areas in acres of different class of surfaces
Corresponding coefficient of runoff
Time Of
Concentration
If rain were to fall continuously at a constant rate and be uniformly distributed over an
impervious surface, the rate of runoff from that surface would reach a maximum rate
equivalent to the rate of rainfall. The time required to reach the maximum or equilibrium
runoff rate is defined as the time of concentration.
The time of concentration depends upon the length of the flow path, the slope, soil cover,
and the type of development.
Determine the initial time of concentration using the nomograph on Attachment 01.
Use a minimum time of concentration of 5 minutes for paved areas and a minimum time of
concentration of 10 minutes for unpaved areas.
Precipitation
The various precipitation amounts during specified time periods at recording stations are
analyzed using common models of probability distributions.
A number of alternative statistical distributions such as Log Pearson Type III, Pearson Type
III, Two-Parameter Lognormal, Three-Parameter Lognormal, and Weibull, Type I, Extreme
Value are used in flood hazard analysis.
Civil Engineering
Practice 670 210 1150
Publication Date 20Sep95
Page 7 of 21
This copy is intended for use solely with
Piping Design Layout Training.
For other purposes, refer to the original document
available through Knowledge Online.
FLUOR DANIEL
STORM DRAINAGE
Intensity Duration
Curves
Use the intensity duration curves available from federal, state, county or local agencies for
the project location. If such curves are not available, construct these curves using Weather
Bureau Technical Paper Number 40 (Continental United States); 42 (Puerto Rico and
Virginia Islands); 43 (Hawaiian Islands); 47 and 52 (Alaska); or NOAA Atlas, Precipitation
- Frequency Atlas of the United States, published by the National Weather Service.
For constructing the curves, given only 1 or 2 points, use the following conversion factors
based on 30 minutes as 1.00:
Duration in
Minutes
Factor
Duration in
Minutes
Factor
5
2.22
40
0.80
10
1.71
50
0.70
15
1.44
60
0.60
20
1.25
90
0.50
30
1.00
120
0.40
To go from 1 curve to another, use the following factors based on the 50 year maximum
rainfall as 1.000:
1 year
0.428
25 years
0.898
2 years
0.455
50 years
1.000
5 years
0.659
100 years
1.108
10 years
0.762
Rainfall intensity duration curves for more than 100 years can be constructed using rainfall
data for periods of 2, 5, 10, 25, 50, and 100 years; and time periods of 20 minutes, 60
minutes, 2 hours, 3 hours, 6 hours, 12 hours; and 24 hours using the following formula:
_
Xji = Xi + Kj Si
_
Xi
where
j
i
Xji
Xi
Kj
Si
=
=
=
=
=
=
Return period in years
Specific storm duration in minutes, hours or days
Precipitation in inches for return period j and duration i
Mean maximum annual storm for duration i
Frequency factor (in standard deviations) for a return period of j years
Standard deviation of maximum annual storm for duration i
For more detailed procedures using this formula, refer to "Analysis of Data," Pages 7 to 25 of
Rainfall Depth Duration Frequency for California, Department of Water Resources, State of
California, November 1982.
A sample set of curves is shown in the sample problems in this practice.
Civil Engineering
Practice 670 210 1150
Publication Date 20Sep95
Page 8 of 21
This copy is intended for use solely with
Piping Design Layout Training.
For other purposes, refer to the original document
available through Knowledge Online.
FLUOR DANIEL
STORM DRAINAGE
Using the initial time of concentration, determine "I" intensity of rainfall in inches per hour
from the intensity duration curve for the plant's geographical location using the proper yearly
rainfall frequency.
Compute Q = CIA.
Refer to sample problems in this practice.
Travel Time
Determine the size of the channel or pipe required to carry Q on the slope of the drain.
Determine the velocity of flow.
Measure the length of flow to the point of inflow of the next subarea downstream. Compute
the time of flow for this reach and add it to the initial time of concentration for the first area
to determine a new time of concentration.
Calculate Q for second subarea, using the new time of concentration and continue in similar
fashion until a junction with a lateral channel is reached.
Start at the upper end of the lateral and carry its Q to the junction with the main channel.
Storm Runoff At
Junction
Compute the Q at the junction.
Tributary area with longer
time of concentration
Tributary area with shorter
time of concentration
QA
QB
TA
TB
IA
IB
Peak Q cfs (cubic feet per second), time of concentration in minutes, rainfall intensity in
inches/hour.
If TA = TB then Qp = QA + QB
TP = TA = TB
If QA > QB then Qp = QA + QB IA
IB
TP = TA
If QA< QB then Qp = QB + QA IB
IA
TP = TB
Qp = Peak Q at junction
Tp = Peak time of concentration at junction
If more than 2 tributary areas are contributing at 1 junction, combine 2 areas at a time and
proceed similarly until tributary areas are combined.
Civil Engineering
This copy is intended for use solely with
Piping Design Layout Training.
For other purposes, refer to the original document
available through Knowledge Online.
FLUOR DANIEL
Practice 670 210 1150
Publication Date 20Sep95
Page 9 of 21
STORM DRAINAGE
DITCHES AND
CHANNELS
Capacity
The capacity of ditches and channels will be calculated using the Manning's equation:
2/3 1/2
Q = 1.486
n r s A
where:
Q
A
=
=
r
=
s
n
=
=
Capacity in cfs
Cross sectional area of flow in square feet
Area of flow
Hydraulic radius =
in feet
Wetted perimeter
Slope of energy grade line in foot per foot
Roughness coefficient
Values of roughness coefficient n for ditches and channels
Lined ditches and channels
n
=
0.014 for poured concrete
n
=
0.016 for shotcrete (gunite)
n
=
0.014 for asphalt
n
=
0.035 for medium weight rip rap
n
=
0.025 for crushed rock
n
=
0.030 for grass
Unlined ditches and channels
n
=
0.020 for very fine sand, silt or loam
n
=
0.025 for sand and gravel
n
=
0.030 for coarse gravel
Values of n for other surfaces can be found in Session 7, Pages 7-17 of King and Brater,
Handbook of Hydraulics, McGraw-Hill Book Company, New York; and Chapter 5, Pages
110 to 113 of Chow, Ven Te, Open-Channel Hydraulics, McGraw-Hill Book Company, New
York, 1959.
Ditches and channels should be designed with the top of the walls at or below the adjacent
ground to allow interception of surface flows.
The minimum velocity of flow should be 2.0 feet per second in order to prevent the settling
of solids, if there is possibility of solids flowing in the ditches and channels.
Velocities in unlined ditches and channels must be limited to prevent cutting or erosion of
the ditch or channel bottom or sides. Permissible channel velocities for various types of soil
can be found in Session 7, Pages 7-19 of King and Brater, Handbook of Hydraulics,
McGraw-Hill Book Company, New York; and Chapter 7, Page 165 of Chow, Ven Te,
Open-Channel Hydraulics, McGraw-Hill Book Company, New York, 1959. If the mean
velocity exceeds that permissible for that particular kind of soil, the channel should be
protected with some type of lining.
Freeboard or additional wall heights are to be added above the calculated water surface.
For ditches and channels with capacities to 50 cfs, add 1.0 feet.
Civil Engineering
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Practice 670 210 1150
Publication Date 20Sep95
Page 10 of 21
FLUOR DANIEL
STORM DRAINAGE
For ditches and channels with capacities from 50 cfs to 200 cfs, add 1.5 feet.
For ditches and channels with more than 200 cfs capacities, refer to Chapter 7, Pages 159
and 160, of Chow, Ven Te, Open-Channel Hydraulics, McGraw-Hill Book Company, New
York, 1959.
For curved alignments, add freeboards above the superelevated water surface.
It is desirable to provide a depth greater than critical. If not possible, an energy dissipator
may be required at the end of the ditch section.
Linings
Ditches and channels with a flow velocity that exceeds permissible velocity will be lined.
Lining of ditches and channels will be poured concrete, gunite, asphalt, crushed rock, riprap,
or other type of slope protection.
For design procedure of riprap design, refer to Chapter 3, Pages III-137 to III-150 of
Virginia Erosion and Sediment Control Handbook, Virginia Department of Conservation
and Recreation Division of Soil and Water Conservation, 1980.
GRAVITY STORM
SEWER SYSTEM
Capacity
The capacity of a gravity storm sewer system will be calculated using the Manning's
equation. Refer to sections covering Ditches and Channels in this practice.
Closed storm sewers should be deigned to flow full for the design storm, unless otherwise
specified by the Client.
The gravity storm sewer system will be designed in such a manner that at the maximum
design flow, the water level in the most remote catch basin of the system or subsystem is a
minimum of 6 inches below top of grating. The controlling elevation at a junction of a main,
lateral, or sublateral for calculating the hydraulic gradeline upstream will be the hydraulic
grade elevation of the main or lateral at the point or the soffit elevation of the pipe,
whichever is greater.
Values of Manning's n for closed sewers are as follows:
Pipe Material
Polyvinyl chloride pipe
Steel
Ductile iron
Cast iron
Cement lined pipe
Concrete pipe
Vitrified clay pipe
Fiberglass reinforced plastic
Corrugated metal pipe
n
0.010
0.011
0.013
0.013
0.015
0.013
0.013
0.010
0.024
Civil Engineering
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FLUOR DANIEL
Practice 670 210 1150
Publication Date 20Sep95
Page 11 of 21
STORM DRAINAGE
The preferred slope for sewer lines will be approximately 0.01 foot (1/8 of an inch) per foot.
The minimum slope will be approximately 0.005 foot (1/16 of an inch) per foot but may be
decreased, if necessary, provided the required minimum velocity is maintained to avoid
disposition of solids.
The minimum pipe size for branch lines will be 4-inch diameter and 8-inch diameter for
catch basin outlet pipes.
The minimum velocity for closed storm sewers should be 2.0 feet per second to prevent the
settling of solids.
For concrete sewers where high velocity flow is continuous and grit erosion is expected to be
a problem, use a maximum velocity of about 10 feet per second.
The alignment chart in Attachment 02 can be used for the solution of Manning's equation for
circular pipes flowing full.
The graph in Attachment 03 is used for the solution of problems involving sewers flowing
only partly filled. The following procedure is used for finding the hydraulic elements of the
pipes.
Compute the ratio of q/Q for each line.
Find the ratio of h/D and v/V.
From the ratio h/D, calculate h.
From the ratio v/V, calculate v.
q
Q
h
D
v
V
=
=
=
=
=
=
Actual flow, cfs
Quantity if pipe flowing full, cfs
Actual depth of flow, feet
Inside diameter of pipe, feet
Actual velocity, fps (feet per second)
Velocity if pipe were flowing full, fps
Losses
Manhole losses will be calculated from the following:
 2
 2
hmh = 0.05  v  to0.75  v 
 2g 
 2g 
depending upon the inlet and outlet pipe size, elevation and design.
Bend losses will be calculated from the following equations:
 2
hb = Kb  v 
 2g 
where
Kb = 2.0  δ 
 90 
where δ = Central angle of bend in degrees.
Bend losses should be included for closed conduits; those flowing partially full as well as
those flowing full.
Civil Engineering
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Practice 670 210 1150
Publication Date 20Sep95
Page 12 of 21
FLUOR DANIEL
STORM DRAINAGE
CULVERTS
Drainage culverts are normally corrugated metal pipe, reinforced concrete pipe, or reinforced
concrete box as necessary to meet the requirements for stormwater drainage flow, truck
loads, and depth of fill above the culvert.
Culverts under roads will be designed to support the earth pressures on the culvert and the
maximum wheel load that will be imposed over it through its design life, plus the applicable
impact, as defined in AASHTO (American Association of State Highway and Traffic
Officials) Standard specifications for Highway Bridges. In the absence of construction or
maintenance vehicles with a greater wheel load, the culvert will be designed to support a
wheel load of 16,000 pounds (HS-20 loading). Minimum cover over culverts will be
12-inches for circular corrugated metal pipe, and 18-inches for reinforced concrete pipe, and
corrugated metal pipe arches.
The minimum size of culvert will be 12-inch diameter for lengths of 30 feet or less and
18-inch diameter for lengths over 30 feet.
Where installation of multiple culverts is required, the minimum clear distance between
pipes will be as follows:
Pipe Diameter
Minimum Clear Distance
12 inch to 24 inch
27 inch to 72 inch
78 inch to 120 inch
12 inches
1/2 diameter
36 inches
Culverts will have a slope that will provide a minimum velocity of 2.0 fps. Culverts will be
sized to pass the 10-year storm flow with unsubmerged inlet. However, the culvert will be
checked for the 50-year storm with ponding at the entrance not to exceed the top of the road
subgrade.
In designing any culvert larger than a 36-inch diameter single-barrel pipe (for example, arch
and oval pipe, multiple-barrel culverts, concrete box), design features such as headwalls,
endwalls, transition structures, and energy dissipators will be selected strictly on the basis of
culvert performance and be economically justified.
Procedure for determining culvert size:
List the design data. Refer to sample problems in this practice.
Estimate first trial size.
Find headwater depth.
Inlet Control: Using Attachments 04, 05, or 06, determine HW/D using the appropriate
entrance scale. Convert HW/D to HW (headwater) by multiplying by D (pipe diameter) in
feet.
Outlet Control: Using Attachment 07, 08, or 09, determine H (head) in feet using the
appropriate value for k(e) as given in the following table:
Civil Engineering
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Practice 670 210 1150
Publication Date 20Sep95
Page 13 of 21
FLUOR DANIEL
STORM DRAINAGE
Entrance Loss Coefficients
Type of Entrance
Coefficient
k(e)
Concrete Pipe
Projecting from fill, socket end (groove end)
0.2
Projecting from fill, square cut end
0.5
Headwall or beadwall and wingwalls
Socket end of pipe (groove end)
Square end
Round radius (radius - 1/2 D)
0.2
0.5
0.2
End section conforming to fill slope
0.5
Corrugated Metal Pipe
Projecting from fill (no beadwall)
0.9
Headwall or beadwall and wingwalls, square edge
0.5
Beveled to conform to fill slope
0.7
Flared end section (available from manufacturer)
0.5
Beadwall, rounded edge
0.1
Solve for HW in the following equation:
HW = H + ho − SoL
For TW (tailwater) elevation equal to or greater than the top of the culvert at the outlet, set
ho equal to TW.
For TW elevation less than the top of the culvert at the outlet, use the following equation or
TW, whichever is greater, where dc, the critical depth in feet, is determined from
Attachment 10 or 11.
ho = dc + D
2
Compare the headwaters for both inlet and outlet control. The higher headwater governs
and indicates the flow existing under the given conditions for the trial size selected.
Select culvert size which keeps headwater depth below allowable limit.
STORMWATER
DETENTION AND
RETENTION
BASINS
Flood Control
Detention Basin
The primary function of the flood control detention basin is to store the storm runoff during
peak flood and reduce the peak discharge.
Civil Engineering
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Practice 670 210 1150
Publication Date 20Sep95
Page 14 of 21
FLUOR DANIEL
STORM DRAINAGE
The flood control detention basin is generally the least expensive and most reliable measure.
It can be designed to fit a wide variety of sites and can accommodate multiple outlet
spillways to control multifrequency outflow.
Measures other than flood control detention basins may be preferred in some locations. Any
device selected, however, should be assessed as to its function, maintenance needs, and
impact.
Design flood control detention basins for 50 years storm frequency.
For flood control detention basin storage volume requirement calculations procedure, for up
to 2,000 acres of drainage area, refer to Chapter 6 Storage Volume for Detention Basins,
Pages 6-1 to 6-11 of Urban Hydrology for Small Watersheds, TR-55, United States
Department of Agriculture, Soil Conservation Service, January 1975, or use local drainage
manual, if available.
Stormwater Retention
Basin
Regulations require management of storm runoff from industrial plant sites so as not to
discharge toxic or hazardous pollutants to receiving waters.
The purpose of stormwater retention basins is to store the stormwater during periods of
storm runoff and release it at a lower rate to the treatment process.
Retention pond and storage basin capacities will be determined based on the total
accumulated stormwater runoff from the design storm frequency for duration of 24 hours. A
minimum freeboard of 12 inches will be provided on top of water surface.
Lining for ponds and basins will be as recommended in the Geotechnical Investigation
Report or as required by process and environmental criteria for the project.
Sediment Control
Basin
Erosion and sediment control measures are required during construction to prevent surface
storm water runoff pollution into stream channels and water bodies.
The sediment control basin is required to collect and store sediment or debris from affected
areas.
The sediment control basin collects and holds stormwater runoff to allow suspended
sediment to settle out.
Design sediment control basins for 10-year storm frequency, unless regulatory agencies
dictate otherwise.
The surface area of the sediment basin at the height of the rim of the riser pipe is calculated
by using the following formula:
A=
KQ
Vs
Civil Engineering
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Practice 670 210 1150
Publication Date 20Sep95
Page 15 of 21
FLUOR DANIEL
STORM DRAINAGE
where
A
Q
K
Vs
=
=
=
=
Basin surface area square feet
Storm runoff cfs
1.2
0.00096 ft/sec settling velocity for a 0.02 millimeter particle size.
Particles greater than or equal to the 0.02 millimeter particle size are to be retained in the
basin.
The sediment storage volume is 75 cu yd per acre of disturbed construction area. The
settling zone will be a minimum of 2 feet deep.
The combined capacities of the riser pipe and spillway are designed to be sufficient to pass
the peak rate of storm runoff of a 10-year storm frequency.
The sediment control basin will need to be periodically cleaned out to restore the basin to its
original designed volume capacity.
A concentric antivortex device and trash rack should be provided on top of the riser pipe.
A concrete base of sufficient weight to prevent flotation of the riser is attached to the riser
pipe with a watertight connection.
Stone riprap protection should be provided on the spillway to reduce erosion of the spillway
dike.
A protection fence should be provided around the sediment control basin for safety.
The sediment control basin may be used after construction as a permanent stormwater
management basin.
For sediment control basin design requirements and procedure, refer to Chapter 3, Pages
III-59 to III-88 of Virginia Erosion and Sediment Control Handbook, Virginia Department
of Conservation and Recreation Division of Soil and Water Conservation, 1980.
STORM DRAINAGE
SOFTWARE
(AVAILABLE
IN IRVINE)
1.
Advanced Designer Series
Civil Soft
Storm Plus
Storm Drain Analysis Program
Storm Plus is based on the original computer program F0515P and was developed in
April 1979. This program was written for use by the Los Angeles County Flood Control
District or by its contractors on district projects.
This program computes and plots uniform and nonuniform steady flow water surface
profiles and pressure gradients in open channels or closed conduits with irregular or
regular sections. The flow in a system may alternate between super critical, subcritical,
or pressure flow in any sequence. The program will also analyze natural river channels
Civil Engineering
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Practice 670 210 1150
Publication Date 20Sep95
Page 16 of 21
FLUOR DANIEL
STORM DRAINAGE
although the principle use of the program is intended for determining profiles in
improved Flood Control Systems.
2.
Haestad Methods
Civil Engineering Software
HEC-1
Flood Hydrograph Package
This computer program was developed by HEC (The Hydrologic Engineering Center),
Corp of Engineers, Department of the Army.
The HEC-1 model is designed to simulate the surface runoff response of a river basin to
precipitation by representing the basin as an interconnected system of hydrologic and
hydraulic components.
Each component models an aspect of the precipitation runoff process with a portion of
the basin, commonly referred to as a subbasin. A component may represent a surface
runoff entity, a stream channel, or a reservoir. The result of the modeling process is the
computation of stream flow hydrographs at desired locations in the river basin.
HEC-1 has several major capabilities which are used in the development of a watershed
simulation model and the analysis of flood control measures. The capabilities are the
following:
Automatic estimation of unit graph, interception/infiltration, and streamflow
routing parameters.
Simulation of complex river basin runoff and streamflow.
River basin simulation using a precipitation depth versus area function.
Computation of modified frequency curves and expected annual damages.
Simulation of flow through a reservoir and spillway for dam safety analysis.
Simulation of dam breach hydrographs.
Optimization of flood control system components.
3.
Haestad Methods
Civil Engineering Software
HEC-2
Water Surface Profiles
This computer program was developed by HEC, Corps of Engineers, Department of the
Army.
The HEC-2 computer program is intended for calculating water surface profiles for
steady, gradually varied flow in natural or manmade channels. Both subcritical and
supercritical flow profiles can be calculated. The effect of various obstructions such as
bridges, culverts, weirs, and structures in the flood plain may be considered in the
computations. The program is also designed for application in flood plain management
and flood insurance studies to evaluate floodway encroachments and to designate flood
hazard zones. Also, capabilities are available for assessing the effect of channel
improvements and levels on water surface profiles.
Civil Engineering
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Practice 670 210 1150
Publication Date 20Sep95
Page 17 of 21
FLUOR DANIEL
STORM DRAINAGE
4.
Haestad Methods
Civil Engineering Software
HEC-Plot
Plotting Program for HEC-1 and HEC-2
HEC-Plot is an enhanced version of the Plot 2 Program of the US Army Corps of
Engineers, written by HEC.
Computer Program HEC-Plot was developed to provide a quick and simple graphical
display of cross section data and computed results from HEC-1 and HEC-2. The
HEC-Plot Program provides the capability to plot cross section data, including the
changes to the section caused by the HEC-2 options that modify section data. HEC-2
profiles and rating curves of the output variables, available on HAESTAD 95 or TAPE
95, can be plotted. HEC-Plot also plots HEC-1 output hydrographs.
5.
Haestad Methods
Civil Engineering Software
Quick HEC-12
Drop Inlet Design and Analysis
Quick HEC-12 handles the following inlet types:
Curb
Grate
Combination curb and grate
4-inch bridge Scupper
Slotted Drain
Grate in trapezoidal ditch
Quick HEC-12 uses the manual procedure outlined by the Federal Highway
Administration, Hydraulic Engineering circular Number 12, Drainage of Highway
pavements, March, 1984.
6.
Haestad Methods
Civil Engineering Software
POND-2
Detention Pond Design and Analysis
POND-2 Computer Program is for detention pond design. It estimates detention storage
requirements, computes a volume rating table for any pond configuration, routes
hydrographs for different return frequencies through alternative ponds and plots the
resulting inflow and outflow hydrographs. POND-2 is completely compatible with
LINK-2 and can automatically import inflow hydrographs from QUICK TR-55, TR-20,
and HEC-1 computer files.
7.
Haestad Methods
Civil Engineering Software
Quick TR-55
Hydrology for small watersheds
Quick TR-55 Computer Program was developed based on the SCS TR-55 Urban
Hydrology for small watersheds. The program can generate and plot hydrographs,
compute peak discharges, and perform predeveloped and postdeveloped analysis.
Civil Engineering
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Practice 670 210 1150
Publication Date 20Sep95
Page 18 of 21
FLUOR DANIEL
STORM DRAINAGE
8.
Haestad Methods
Civil Engineering Software
TR-20
Project Formulation Hydrology
The TR-20 Computer Program is a single-event model which computes direct runoff
resulting from any synthetic or natural rainstorm. It develops flood hydrographs from
runoff and routes the flow through steam channels and reservoirs. The following major
Civil Engineering software programs from Haestad Methods are also available:
9.
HECWRC
Flood Flow Frequency
10. HMR52
Probable Maximum Storm
11. WSP-2
Water Surface Profiles
12. Hy-4-69
Hydraulics of Bridge Waterways
13. WSPRO (Hy-7)
Bridge Waterways Analysis Model
14. DAMS 2
Structure Site Analysis
15. THYSYS
Culverts Storm Sewer and Inlets
16. SWMM
Storm Water Management Model
17. HEC-6
Scour and Deposition
18. SEDIMOT II
Hydrology and Sedimentology
19. HYDRA
Storm and Sanitary Sewer Analysis Software
PITZER
HYDRA is one of the most practical programs available to analyze storm and sanitary
sewer collection systems. It is structured to work well on both large municipal systems
and small tracks, with or without database files and without or within AutoCAD.
HYDRA allows the designer to generate storm flows by the Rational Method, a modified
SCS Method (Soil Conservation Service) or by continuous simulation. The best method
to use depends upon the situation, available data, and the requirements of the
municipality.
Civil Engineering
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Practice 670 210 1150
Publication Date 20Sep95
Page 19 of 21
FLUOR DANIEL
STORM DRAINAGE
REFERENCES
AASHTO (American Association of State Highway and Traffic Officials).
Analysis of Data, Pages 7 to 25 of Rainfall Depth Duration Frequency for California,
Department of Water Resources, State of California, November 1982.
Bureau of Engineering Manual. Part G, Storm Drain Design. City of Los Angeles,
Department of Public Works.
Capacity Charts For the Hydraulic Design of Highway Culverts. Hydraulic Engineering
Circular Number 10. Mar. 1965.
Chow, Ven Te. Handbook of Applied Hydrology. McGraw-Hill Book Company. 1964.
Chow, Ven Te. Open-Channel Hydraulics. McGraw-Hill Book Company. New York.
1959.
Design and Construction of Sanitary and Storm Sewers. American Society of Civil
Engineers. WPCF Manual of Practice Number 9. 1972.
Design Manual. Hydraulic. Los Angeles County Flood District.
Design Manual. Orange County Flood Control District.
Engineering Field Manual. United States Department of Agriculture. SCS. Washington,
DC. 1989.
Estimating Probabilities of Extreme Floods: Methods and Recommended Research.
National Research Council. Washington, DC. 1988.
Guide For Sediment Control on Construction Sites in North Carolina. United States
Department of Agriculture. Soil Conservation Service, SCS. North Carolina. 1973.
Guidelines For Determining Flood Flow Frequency. Interagency Advisory Committee on
Water Data, Bulletin #17b of the Hydrology Subcommittee, VA. 1982.
Gumbel, E. J. Statistics of Extremes. Columbia University Press. New York. 1958.
Hydraulic Charts For the Selection of Highway Culverts. Hydraulic Engineering Circular
Number 5. Dec 1965.
Hydraulic Design of Improved Inlets For Culverts. Hydraulic Engineering Circular Number
13. Aug 1972.
Hydrology Manual. Los Angeles County Flood Control District.
Hydrology Manual. Orange County Flood Control District.
Hydrology Manual. Riverside County Flood Control and Water Conservation District.
King and Brater. Handbook of Hydraulics. McGraw-Hill Book Company. New York.
Kite, G. W. Frequency and Risk Analysis in Hydrology. Water Resource Publication.
Littleton, CO. 1977.
Manual For Erosion and Sediment Control in Georgia. Georgia Soil and Water
Conservation Committee. 1975.
Civil Engineering
This copy is intended for use solely with
Piping Design Layout Training.
For other purposes, refer to the original document
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Practice 670 210 1150
Publication Date 20Sep95
Page 20 of 21
FLUOR DANIEL
STORM DRAINAGE
Manual of Standards For Erosion and Sediment Control Measures. Association of Bay Area
Governments. Jun 1981.
Maryland Erosion and Sediment Control Handbook. United States Department of
Agriculture, SCS. College Park, MD. 1975.
National Engineering Handbook. Drainage of Agricultural Land. United States Department
of Agriculture, SCS. Washington, DC. 1971.
National Engineering Handbook. Hydraulics. United States Department of Agriculture,
SCS. Washington, DC. 1975.
National Engineering Handbook. Hydrology. United States Department of Agriculture.
SCS (Soil Conservation Service). Washington, DC.
NOAA Atlas, Precipitation - Frequency Atlas of the United States, published by the National
Weather Service.
Rainfall Depth Duration Frequency For California. Department of Water Resources. State
of California. Nov 1982.
Urban Hydrology For Small Watersheds. TR-55. United States Department of Agriculture.
Soil Conservation Service. Jan 1975.
Urban Runoff. Erosion and Sediment Control Handbook. United States Department of
Agriculture. Soil Conservation Service, SCS. St. Paul, MN. 1976.
Virginia Erosion and Sediment Control Handbook. Virginia Department of Conservation
and Recreation Division of Soil and Water Conservation. 1980.
Water Resources Technical Publication. Research Report Number 24. United States
Department of The Interior, Bureau of Reclamation.
Weather Bureau Technical Paper
Number 40
Number 42
Number 43
Number 47
Number 52
ATTACHMENTS
Attachment 01:
Overland Flow Time
Attachment 02:
Alignment Chart For Manning Formula For Pipe Flow
Attachment 03:
Relative Velocity And Flow In Circular Pipe For Any Depth Of Flow
Attachment 04:
Headwater Depth For Concrete Pipe Culverts With Inlet Control
Civil Engineering
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Practice 670 210 1150
Publication Date 20Sep95
Page 21 of 21
FLUOR DANIEL
STORM DRAINAGE
Attachment 05:
Headwater Depth For CM Pipe Culverts With Inlet Control
Attachment 06:
Headwater Depth For CM Pipe Arch Culverts With Inlet Control
Attachment 07:
Head For Concrete Pipe Culverts Flowing Full
Attachment 08:
Head For Standard CM Pipe Culverts Flowing Full
Attachment 09:
Head For Standard CM Pipe Arch Culverts Flowing Full
Attachment 10:
Critical Depth Circular Pipe
Attachment 11:
Critical Depth Standard CM Pipe Arch
Attachment 12:
Form: 000.210.F8000:
Rational Method Calculation Form
Attachment 13:
Form: 000.210.F8001:
Peak Q At The Junction Calculation Sheet
Attachment 14: (12Mar93)
Form: 000.210.F5000: Datasheet - Culvert Design
Civil Engineering
Client Name:
Project Name:
Project Number:
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FLUOR DANIEL
FORM 000 210 F5000 (12Mar93)
Page 1 of 1
DATASHEET - CULVERT DESIGN
STORM DRAINAGE
DATE:
REV.:
Culvert Station
Hydrology:
(
(
cfs
cfs
Year Frequency), Q1 =
Year Frequency), Q2 =
Headwater
Maximum Allowable
Q = Design Discharge
Q = Check Discharge
Elevation
AHW =
TW =
SO =
Elevation
L
Elevation
NOTES:
1. h O =
DESIGN SELECTION
dc + D
or TW, Whichever is Greater
2
2. HW = H + h O - S
O
L
Culvert Identification
Entrance
Material
Q
Size
Inlet Control
HW
D
HW
(ft)
Outlet Control
H
hO
(Note 1)
SO L
Comments
HW
(ft)
(Note 2)
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Practice 670 210 1160
Publication Date 20Sep95
Page 1 of 10
FLUOR DANIEL
SANITARY SEWER SYSTEMS
PURPOSE
This practice establishes the parameters of the various components involved in the design of
gravity and force main sanitary sewer systems.
Design of these systems will require compliance with regulations and standards of various
private and public agencies and applicable federal, state, county and city regulations. The
design data, dimensions, regulations and standards will reflect a considerable diversity
between owner and government agencies.
The Civil Engineer must review these various regulations and standards and select the
appropriate ones for the project. This technical practice should be used in conjunction with
textbooks and other publications on the subject, such as those listed in the references. The
design engineer should stay updated on materials, specifications, and design criteria.
SCOPE
This practice includes the following major sections:
SEWAGE FLOWRATES
GRAVITY SEWER DESIGN
MANHOLES
PUMPING STATIONS
SIPHONS
HYDRAULIC DESIGN
EXAMPLE PROBLEM
REFERENCES
ATTACHMENTS
APPLICATION
This practice provides guidelines for the design of sanitary sewers and applies to all projects
and work assignments being performed by Fluor Daniel Civil Discipline. The Lead Civil
Engineer on a project is responsible for the use of these guidelines in designing sanitary
sewer systems.
SEWAGE
FLOWRATES
Domestic sewage quantities normally are to be computed on a contributing population basis,
except as noted in subparagraph d and e on page 3-1 of Hydraulic Design of Sewers.
Subparagraph d (Industrial Waste Flows)
Such industries cannot be computed totally on a population or fixture unit basis.
Industrial waste sewers and sanitary sewers will be designed for the peak industrial flow
as determined for the particular industrial process or activity involved.
Civil Engineering
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Practice 670 210 1160
Publication Date 20Sep95
Page 2 of 10
FLUOR DANIEL
SANITARY SEWER SYSTEMS
Subparagraph e (Fixture Unit Flow) The size of building connections, including those
from theaters, restaurants, chapels, clubs and other such buildings, will, in all cases, be
large enough to discharge the flow computed on a fixture unit basis.
The population to be used in design depends upon the type of area which the sewer
serves. If the area is entirely residential, the design population is based on full
occupancy. If the area served is entirely industrial, the design population is the greatest
Average Daily
Per Capita
Sewage quantities for different types of installations are shown on page 3-1 of Hydraulic
Design of Sewers. The average daily flow will be computed by multiplying the resident and
nonresident contribution populations by the appropriate per capita allowances and adding the
two flows.
Nonresidents working 8 hour shifts will be allowed 30 gallons per capita per day.
Flowrate
The average hourly flowrate should be used when designing sewers to serve small areas of
the installation where several buildings or a group of buildings are under consideration and
where the majority of sewage is generated by nonresidents or other short term occupants.
The peak daily or diurnal flowrate is an important factor in sewer design, especially when
minimum velocities are to be provided on a daily basis. The peak diurnal flowrate will be
taken as 1/2 of the extreme peak flowrate.
Extreme flowrates of flow occasionally and must be considered. Sewers will be designed
with adequate capacity to handle extreme peaks flowrates, ratios of extreme peak flowrates at
average flow will be calculated with the use of the following formula:
R = C 0.67
Q
where
R
Q
=
=
C
=
Ratio of extreme peak flowrate to average
Average daily flow or average hour flowrate in million gallons per
day, gallons per day or gallons per hour
Constant 3.8 for MGD, 38.2 for GPD, or 22.5 for GPH
Infiltration And
Inflow
In computing wastewater flows for new sewer design, allowances for groundwater
infiltration will be 500 to 1,000 gallons per day per inch diameter per mile of pipe and will
be added to the peak rate of flow.
Civil Engineering
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Practice 670 210 1160
Publication Date 20Sep95
Page 3 of 10
FLUOR DANIEL
SANITARY SEWER SYSTEMS
Fixture Unit Flow
The size of building connections will be large enough to discharge the flow computed on a
fixture unit basis. This requirement applies to building connections only and not to the
lateral or other sewers to which they connect.
GRAVITY SEWER
DESIGN
Generally, it is not desirable to design sewers for full flow even at peak rates. Trunk and
interceptor sewers will be designed to flow at depths not exceeding 90 percent of full depth;
lateral and main sewers 80 percent; and building connections, 70 percent. However,
regardless of flow and depth, the minimum sizes to be used are 6 inch for building
connections and 8 inch for all other sewers.
The Manning formula will be used for design of gravity sewers:
2/3 1/2
V = 1.486
n R S
where
V
n
R
S
=
=
=
=
Velocity in feet per second
Coefficient of pipe roughness
Hydraulic radius in feet
Slope of energy line in feet per foot
Values of n (roughness coefficient) to be used in the formula range from 0.013 to 0.015, with
the lowest n value applying to new or relatively new pipe. Values of n will also depend on
the pipe material. Variation of n with depth of flow has been shown experimentally, and can
be considered in designing sewer to flow partially full.
Velocity
Sewers will be designed to provide a minimum velocity of 2.0 FPS (feet per second) at the
average daily flow, or average hourly flowrate, and minimum velocity of 2.5 to 3.5 FPS at
the peak diurnal flowrate.
Pipe Cover
Adequate cover will be provided for frost protection and against structural damage due to
any superimposed surface loading.
Hydraulic Profile
In most cases where small to medium sized gravity sewers are installed in long runs, it will
be safe to assume uniform flow throughout the entire length of pipe. A hydraulic profile is
recommended showing all the other utilities crossing the sewer line. Sewer plans generally
will be oriented so that the flow in the sewer is from right to left on the sheet and stationing
is upgrade from left to right. Each sewer plan should include a north arrow. Match lines
should be easily identifiable.
Civil Engineering
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Piping Design Layout Training.
For other purposes, refer to the original document
available through Knowledge Online.
FLUOR DANIEL
Practice 670 210 1160
Publication Date 20Sep95
Page 4 of 10
SANITARY SEWER SYSTEMS
Critical Flow
Gravity sewers will ordinarily be designed to maintain subcritical flow conditions in the pipe
throughout the normal range of design flows. However, there are exceptions in which
supercritical flow may be required and will be justified.
Hydrogen Sulfide
In Sewers
Two of the most important problems occurring in wastewater collection systems are the
corrosion of sewers and appurtenances, and the propagation and emission of odors and toxic
gases. Both of these problems can be attributed in large part to the generation of hydrogen
sulfide (H2S) in sewers. Sewers will be designed hydraulically in accordance with U.S. EPA
(Environmental Protection Agency) guidelines established therein to prevent excessive
generation of hydrogen sulfide.
Corrosion Control
Plastic pipe PVC (Polyvinyl Chloride); HDPE (High Density Polyethylene); ABS
(Acrylonitrile-Butadien-Styrene), fiberglass, and vitrified clay pipe are best suited for
corrosive environments, whereas concrete (including ABS composite), asbestos cement,
ductile iron, and cast iron soil pipe should be avoided unless a special protective lining,
coating or treatment are provided.
MANHOLES
Sanitary sewer manholes will be spaced 300 to 400 feet. When the size is large enough to
permit a man to enter, a spacing of 500 feet may be used. Manholes should be located at the
junctions of sewers and changes in grades, sizes, or alignment. Manholes may be precast
concrete (assembled in the field) cast in place, or brick.
PUMPING
STATIONS
Pumping station and pneumatic ejectors will normally be required to remove waste from
areas which cannot be served hydraulically by gravity sewers. In certain situations, however,
a gravity sewer system can be used, but only at the expense of deep trench excavation. Both
wastewater pumping and gravity flow sewers may be technically feasible and capable of
meeting service requirements, however, they may not be equivalent in economic terms.
When it is not readily apparent which solution would be more economical, the decision to
use one or the other should be based on life cycle cost analysis. Initial capital and
construction costs for pumps, ejectors, structures, force main, plus operation and
maintenance costs should be compared with cost of deep trench excavation or other special
construction methods required for a gravity system. Generally, a gravity sewer system will
be justified until its cost exceeds the cost of a pumped system by 10 percent.
Civil Engineering
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Practice 670 210 1160
Publication Date 20Sep95
Page 5 of 10
FLUOR DANIEL
SANITARY SEWER SYSTEMS
Pumping Equipment
Pumping equipment used in sanitary sewer systems may be classified into two general types;
centrifugal pumps and pneumatic ejectors. The latter are used only in the smaller
installations where centrifugal pumps, if used, would be too large for the application.
Centrifugal pumps fall into the following three general classifications:
Axial - flow or propeller pumps
Mixed Flow or angle - flow pumps
Radial - flow pumps (commonly referred to as centrifugal pumps)
The classification into which a pump falls usually can be determined by its specific (Ns) at
the point of maximum efficiency.
The specific speed of an impeller may be defined as the speed in rpm (revolution per minute)
at which a geometrically similar impeller would run if it were of such size as to deliver
1 gpm against 1 foot of head.
The formula for specific speed is as follows:
Ns =
RPM GPM
H 3/4
where H is in feet.
Pump Construction
Most pump casings are made of cast iron. Although for special applications where gritty or
corrosive liquids are involved, other materials sometimes are specified.
Pneumatic ejectors are usually used for lifting sewage from basement of buildings and small
lift stations where their advantage outweigh their low efficiency, which is limited to about 15
percent. Their advantages are the following:
Sewage is completely enclosed an consequently no sewer gases can escape except
through the vent.
Operation is fully automatic and the ejector goes into service only when needed.
The relatively few moving parts in contact with sewage require little attention or
lubrication.
Ejectors are not easily clogged.
The following is an empirical formula for the approximate capacity of air required to operate
an ejector:
V=
Q(H + 34)
250
where
V
H
Q
=
=
=
volume of free air required in CFM
total head in feet
rate of sewage discharge in GPM
Civil Engineering
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Practice 670 210 1160
Publication Date 20Sep95
Page 6 of 10
FLUOR DANIEL
SANITARY SEWER SYSTEMS
Datum
All readings for suction lift, suction head, discharge head, and net positive suction head are
taken with reference to the datum which in the case of horizontal shaft, is the elevation of
the pump center line and in the case of vertical shaft pumps is the elevation of the entrance
eye of the suction impeller.
Suction Lift (Hs)
Suction lift exists where the total suction head is below atmospheric pressure. Total suction
lift, as determined on test, is the reading of a liquid manometer at the suction nozzle of the
pump converted to feet of liquid and referenced to datum, minus the velocity head at the
point of gage attachment.
Suction Head (Hs)
Suction head exists, when the total suction head is above atmospheric pressure, as
determined on test, it is the reading of the gage at the suction of the pump converted to head,
in feet, at the point of gage attachment.
Total Discharge
Head (Hd)
Total discharge head is the reading of a pressure gage at the discharge of the pump,
converted to feet of liquid and referred to datum, plus the velocity head at the point of gage
attachment.
Total Head (H)
Total Head (H) is sometimes referred to as total dynamic head or TDH. Total head is the
measure of the energy increase per pound of the liquid imparted to it by the pump and is
therefore the algebraic difference between the total discharge head and the total suction head.
Total head as determined on test where suction lift, and, where positive suction head exists,
the total head is the total discharge head minus the total suction head.
NPSH (Net Positive
Suction Head)
The NPSH is the total suction head, in feet of liquid absolute, determined at the suction
nozzle and referred to datum, less the vapor pressure of the liquid in feet absolute.
SIPHONS
The siphon in sewerage practice almost invariably refers to an inverted siphon or depressed
sewer which would stand full even with no flow. Its purpose is to carry the flow under an
obstruction such as stream or depressed highway and to regain as much elevation as possible
after the obstruction has been passed.
Civil Engineering
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Practice 670 210 1160
Publication Date 20Sep95
Page 7 of 10
FLUOR DANIEL
SANITARY SEWER SYSTEMS
Single And Multiple
Barrel Siphons
It is common practice, at least on large sewers, to construct multiple barrel siphons. The
objective is to provide adequate self-cleaning velocities under widely varying flow
conditions. The primary barrel is designed so that a velocity of 2 to 3 feet per second will be
reached at least once each day, even during the early years of operation. Additional pipe
regulated by lateral overflow weirs assist progressively in carrying flows of greater
magnitude, that is maximum dry weather flow to maximum storm flow.
Profile
Two considerations which govern the profile of a siphon are provision for hydraulic losses
and ease of cleaning. The friction loss through the barrel will be determined by the design
velocity. For calculating the head loss it is sound conservative Hazen-Williams C of 100
(Manning n from 0.014 for small sizes to 0.018 for the largest). Siphons may need cleaning
more often than gravity sewers. For easy cleaning, siphons should not have any sharp bends
either vertical or horizontal; only smooth curves of adequate radius should be used.
HYDRAULIC
DESIGN
The first step in the hydraulic design of a sanitary sewer system is to prepare a map showing
the locations of all required sewers and from which the tributary can be shown. Preliminary
profiles of the ground surface along each line are also needed. They should show the critical
elevations which will establish the sewer grades, such as basements of low lying buildings.
topographic maps are useful at this stage of the design.
Sanitary sewer design computation, being repetitious may best be done on tabular forms.
The attached tabulation form is fairly comprehensive and can be adapted to the particular
need of the designer. In using this form for sanitary sewer design, supplementary graph or
tables are required to calculate wastewater flows and hydraulic data. It is recommended that
all flows should be converted to cubic feet per second (CFS). Calculations should start from
the highest elevation and proceed downward. Each building sewer outlet should be shown
and be connected to the nearest sanitary sewer manhole.
There is a tendency on the part of some designers to increase the size of the sewer in order to
obtain a theoretical velocity of 2 feet per second when the available slope would not produce
this velocity in a smaller pipe. Actually, in the larger pipe, the depth of flow would be
decreased to such extent that the velocity might be no greater, and perhaps less, than in a
smaller pipe laid on the same slope. In such cases, the net result of increasing the pipe size
would be to increase the cost without improving the flow conditions. Errors of this nature
can usually be eliminated through analysis of the velocity at various rates of flow.
Civil Engineering
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Practice 670 210 1160
Publication Date 20Sep95
Page 8 of 10
FLUOR DANIEL
SANITARY SEWER SYSTEMS
EXAMPLE
PROBLEM
Refer To
Attachment 07:
Column 1 (Total Discharge in GPMs [Gallons Per Minute]) was taken from the 3 buildings
having a total of 236 fixture units designed by the mechanical department. With the use of
the supply demand curve (Refer to Attachment 01), it will read 98.16 GPM.
Column 2, Size of Pipe; Column 3, Length of Line in Feet; Column 4, Slope of Pipe in
Percent; and Column 5, Velocity Flowing Full, use slope of 2.0 percent.
Column 4 and 5 use pipe flow chart (Refer to Attachment 02) = 4.5 FPS.
Column 6 (Discharge Flowing Full) = 1.52 CFS.
Column 7, convert (Column 1) 98.16 GPM into CFS = 98.16 x 0.002228 = 0.2187 CFS =
21.87 (1/100) average flow to be 1/3.8 peak flow = 21.87/3.8 = 5.76 (1/100) CFS.
Column 8 (peak flow 1/100 CFS) = 98.17 GPM x 0.002228 = 0.2187 CFS = 21.87 1/100
CFS.
Column 9 (Discharge Average %) = (Column 7) 5.76 divided by (Column 6) 1.52 = 3.79
CFS.
Column 10 (Discharge Peak %) = (Column 8) 21.87 divided by (Column 6) 1.52 = 14.39
CFS.
Column 11 (Velocity Average %) = use proportionate flow chart on Attachment 03. Column
9 (3.79 discharge to velocity) = 0.46 FPS.
Column 12 (Velocity Peak %) = use proportionate flow chart on Attachment 03. Column 10
(14.39 discharge to velocity) = 0.70 FPS.
Column 13 (average flow velocity FPS) = (Column 11) 0.46 x (Column 5) 4.5 = 2.07 FPS.
Column 14 (Peak Flow Velocity FPS) = Column 12 0.70 x Column 5 4.5 = 3.15 FPS.
Column remarks, the designer will show the total discharge that are being added on that
particular line.
As specified previously, the pipe should not be designed flowing full. Attached are graphs to
be used in calculating the hydraulic elements. To use Hydraulic Elements Graph in
Attachment 04 for circular pipe.
Example:
Flows will be known, extreme peak, diurnal peak and average daily flow.
Extreme Peak
Diurnal Peak
Average Daily
Q
S
12" Diameter
n
=
=
=
=
=
1.71 CFS
0.91 CFS
0.44 CFS
1.71
0.003
=
0.013
Civil Engineering
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Practice 670 210 1160
Publication Date 20Sep95
Page 9 of 10
FLUOR DANIEL
SANITARY SEWER SYSTEMS
From Attachment 05, for 12 inch the discharge is 2.0 CFS and the velocity is 2.53 FPS.
1.71 = 0.86 then on Attachment 04 hydraulic elements, with the use of this graph plot 0.86
2.0
= d/D = 0.71 is less than the lateral and main sewer 0.80. using the same line proceed to the
right where it intersects the dash line for velocity and it reads 1.14. 1.14 x 2.53 = 2.88 FPS.
Same procedure will be performed for the other flows. The minimum velocity for average
flow is V = 2.0 FPS. Q = 0.44 CFS = 0.44 = 0.22 from Attachment 04 = d/D = 0.33. 0.79 x
2.00
2.53 = 2.0 FPS for average flow.
REFERENCES
Design and Computation of Sanitary and Storm Sewers. ASCE Manual and Reports on
Engineering. ASCE. Practice Number 37.
Domestic Wastewater Treatment. Department of the Army Technical Manual (TM
5-814-3).
Engineering Manual. Part VIII, Chapter 1. Corps of Engineers.
Hydraulic Design of Sewers. Department of the Army Technical Manual (TM 5-814-1).
Plumbing. Engineering Manual. EM 1110-345-165. Corps of Engineers.
Sanitary and Industrial Wastewater Collection - Pumping Stations and Force Mains.
Department of the Army Technical Manual (TM 5-814-2).
Selye, E.E. Book of Design.
Sewerage Treatment Plant Design. ASCE Manual and Reports on Engineering. ASCE
Practice Number 34.
Steel and McGhee. Water Supply And Sewerage.
These standards provide guidelines for the design of sanitary sewers and applies to all
projects and work assignments being performed by the Fluor Daniel Civil Discipline.
ATTACHMENTS
Attachment 01:
Supply Demand Curve
Attachment 02:
Pipe Flow Chart
Attachment 03:
Proportionate Flow Chart (Manning's Formula)
Attachment 04:
Hydraulic Elements Graph for Circular Sewers
Attachment 05:
Alignment Chart for Manning Formula for Pipe Flow
Civil Engineering
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Practice 670 210 1160
Publication Date 20Sep95
Page 10 of 10
FLUOR DANIEL
SANITARY SEWER SYSTEMS
Attachment 06:
Critical Depth of Flow and Specific Head In Rectangular And Circular Conduit
Attachment 07:
Typical Computation Form
Civil Engineering
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Practice 670 210 1200
Publication Date 20Sep95
Page 1 of 6
FLUOR DANIEL
OUTSIDE UNDERGROUND PIPING
PURPOSE
This practice establishes the general layout and design guidelines for outside underground
piping and should be used for basic design. This practice will benefit Civil, Process, and
Piping Design Engineers, but also can be of assistance to other disciplines as well. It is the
responsibility of the Lead Engineer to ensure application and utilization of this practice.
SCOPE
This practice includes the following major sections:
DOMESTIC WATER (POTABLE)
SANITARY SEWERS
OIL WATER DRAINAGE
COOLING WATER
FIREWATER
NATURAL GAS
PIPE MATERIALS
PIPE BEDDING
PIPE SETTLEMENT
REFERENCES
APPLICATION
This technical practice should be utilized by engineers and designers when locating outside
underground piping facilities for industrial or process uses as well as commercial and
residential uses. The practice should be used in conjunction with job specifications, client
specifications, and specifications established by the local Purveyor or Government agency
and is not intended to override any of the aforementioned guidelines unless none exist.
DOMESTIC
WATER
(POTABLE)
In general, domestic water lines should be located on the side of the road that provides the
shortest service connections. These lines should not be located under paved or heavily
traveled areas.
Horizontal separation of domestic water lines and other utility lines should be a minimum of
10 feet to avoid potential contamination. If possible, it should be located in its own
easement. Domestic water lines should not be located in the same trench with other utilities.
When domestic water lines cross other utilities, there will not be a joint within 3 feet in
either direction of the crossing. The water line should be located at an elevation higher than
other utilities, when at all possible. If the water line must cross underneath other utilities,
the other pipeline should be enclosed in concrete or incorporate the use of pressure rated
pipe.
Civil Engineering
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Practice 670 210 1200
Publication Date 20Sep95
Page 2 of 6
FLUOR DANIEL
OUTSIDE UNDERGROUND PIPING
Minimum cover should be 4 feet under heavily traveled roads or railroads. In other
nonstructural areas, 3 feet minimum cover is acceptable. Domestic water lines should
always be located below frost depth.
SANITARY
SEWERS
Sanitary sewers are usually gravity flow and should be located vertically and horizontally
before pressure pipelines.
Sanitary sewers may be located at the centerline of roadways to help avoid conflicts with
other pipelines located on either side of the roadway.
It is preferable to locate sanitary sewers outside of roadways to avoid having to excavate
roadways when repairing or replacing pipe.
In many cases, flat sites may require a sanitary sewer lift station and force main system
installed. The force main should be treated as a pressure line normally located next to
roadways in a dedicated casement or corridor.
Manholes on gravity lines should be used for changes in direction or slope and for
maintenance access and should be spaced at approximately 300 feet for lines up to 12 inches
in diameter and 500 feet maximum for lines larger than 12 inches in diameter.
Minimum cover should be 4 feet for lines under heavily traveled roadways or railroads and 3
feet in nonstructural areas. For larger sanitary sewer mains (12 inches and above), it is not
necessary for the top of the line to be below frost depth. The centerline or Springline should
be at or below the frost line to avoid frost heave problems and provide satisfactory bedding.
Also refer to Practice 670.210.1160: Sanitary Sewer Systems, for more detailed sanitary
sewer design.
Storm Sewers Surface Runoff
Storm water runoff is normally collected via overland flow in ditches and culverts designed
by the Civil Discipline. Many projects require enclosed stormwater systems with catch
basins and manholes located as required. Clean stormwater should be discharged into
natural site drainageways as much as possible.
Stormwater runoff during construction may require a runoff pond to settle the solids and let
the clear stormwater flow into the natural waterway. The governing laws on erosion control
should be followed.
In areas where hydrocarbon or other hazardous liquids or materials are present, catch basins
or trench drains should be utilized so as to collect the flow. These hazardous materials
should be piped to the appropriate waste treatment facilities.
Civil Engineering
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Practice 670 210 1200
Publication Date 20Sep95
Page 3 of 6
FLUOR DANIEL
OUTSIDE UNDERGROUND PIPING
Storm Drainage
Within Tanks
Compound Areas Arrange grading in tank farm areas so that the surface slopes at a
minimum of the 1 percent away from the tank to swales or ditches along the sides of the
enclosure.
Where there are 2 rows of tanks, the pipeway is normally run down the center. Provide a
high point under the pipeway to prevent liquid spills from collecting there.
Terminate the drainage ditches or swales at the corners of the tank enclosure. Provide a
minimum 8 inch drain pipe from this point through the dike with a gate valve or indicator
post valve outside of the enclosure. The drain valve should discharge to the storm ditches.
This valve is normally kept closed and is used only after a rainstorm to discharge
accumulated clean water.
Provide a valved branch line from a point upstream of the drain valve which will give the
operator the option of discharging the tank enclosure to an oily water sewer in the event of a
spill of contamination.
In cold climates, arrange the piping so that water does not stand against closed valves.
OIL WATER
DRAINAGE
Storage tanks are normally provided with a drain valve at the bottom of the tank to permit
periodic drawoff of water which normally collects in the product. The water drawoff valve
should be positioned over an open concrete box with an outlet discharging into the oily water
collection system.
The collecting sewer for a group of tanks is run under the center portion of the compound
and a gate valve or indicator post valve operable outside of the compound is provided. This
valve is normally kept closed so that in the event of spill or tank rupture, the commodity
remains inside the diked enclosure and does not run into the cleanwater storm sewer system.
Routing Of
Clean And Oily
Water Sewers
Routing for main lines from process areas to waste treatment areas should run parallel to
roads and not directly underneath. Where space permits, an easement or corridor alongside
the road should be provided. Avoid routing large mains down the center of roads as it could
potentially leave trenches open for long periods of time. It should be noted that storm sewer
lines alongside of roads also can sustain heavy loads during the construction process.
Consider keeping large trench excavations clear of construction work and access areas. If
possible, discuss routing of all major (24 inches and larger) underground lines with
Construction Manager.
Verify whether or not sewer lines under roads and millroads will sustain earth and traffic
loads. Refer to Practice 670.210.1210: Loads On Underground Pipe.
Civil Engineering
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Practice 670 210 1200
Publication Date 20Sep95
Page 4 of 6
FLUOR DANIEL
OUTSIDE UNDERGROUND PIPING
For large sewer mains, it may not be necessary for the top of the line to be below frost depth.
It is obvious the volumes of water that are flowing in these larger mains are not about to
freeze. To avoid frost heave problems and provide satisfactory bedding, the centerline or
Springline should be at or below the frost line.
Manholes And
Invert Elevations
Provide manholes to access and maintain the system and in accordance with the
requirements set forth in the contract specifications. When separate major groups of storage
tanks, process blocks, and loading facilities are involved, sealed and vented manholes will be
required at strategic points to sectionalize the system.
Sewer invert elevations are set by the slope and size of the line handling the design flow and
is a compromise between a larger line at a flat slope or a smaller line at a steeper slope.
The starting and terminating elevations of the system play an important role in the above
choice. To meet the hydraulic requirements, the system should terminate so that the top of
pipe is 2 to 3 inches higher than the maximum water level in the receiving body of water or,
if an existing sewer, the water level in the manhole.
COOLING
WATER
This system is run underground where the line sizes are large and soil conditions permit.
The supply line starts at the cooling water pumps. Downstream of the associated valving, it
drops underground.
Routing of the supply and return line should parallel main roads running between the
cooling tower and the process area units. The most economical route should be selected with
the same considerations given to these lines as described in the section preceding.
These headers usually run for long distances and depth of cover should be kept to a
minimum giving consideration to the following:
Top of pipe to be at or below frost line.
At least 2 feet minimum cover and more, if necessary, to sustain construction traffic
loads.
Flat turn at changes of direction are preferred, provided all other piping and electrical
ducts in the area can be set to avoid interference.
Spacing of parallel cooling water headers:
- To avoid heat transfer, provide clear space as follows:
-- 18-inches between 24-inches and smaller headers
-- 24-inches between 30-inches and larger headers
FIREWATER
The design responsibility of underground firewater systems varies from office to office
depending on available expertise. Detailed design of these systems are performed by Fire
Civil Engineering
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Practice 670 210 1200
Publication Date 20Sep95
Page 5 of 6
FLUOR DANIEL
OUTSIDE UNDERGROUND PIPING
Protection personnel. The Civil Discipline, as a minimum, provides coordination in the final
system layout and often shows the fire loop and building run-ins on the civil underground
utilities plan.
NATURAL GAS
In General, natural gas pipelines are run underground and can be laid out in the form of a
connected loop whenever possible dependent on those facilities requiring gas service.
The mains should be located under or just outside the road shoulders or in a separate
easement or utility corridor, whenever possible.
Separation should be a minimum of 5 feet from pipelines or facilities containing
nonhazardous materials and a minimum of 10 feet from facilities containing hazardous
materials. It should be noted that many local agencies and codes require separation which
are more strict than those mentioned above.
Depth of bury should be at least 3 feet in potential traffic areas to avoid high traffic loading.
Cathodic protection should always be considered for steel pipe, especially in areas with
potentially high soil electrolysis. Coordinate with the electrical discipline.
PIPE
MATERIALS
Several pipe materials are available on the current market and are applicable to a wide
variety of uses. The most common include the following:
PVC
DIP
VCP
CIP
RCP
CMP
HDPE
Polyvinyl Chloride Pipe
Ductile Iron Pipe
Vitrified Clay Pipe
Cast Iron Pipe
Reinforced Concrete Pipe
Corrugated Metal Pipe
High Density Polyethylene Pipe
PIPE BEDDING
When suitable soil is encountered in a trench excavation, it can be used for pipe bedding if it
meets the requirements of Specification 670.210.02224: Excavation, Backfill, And
Compaction For Underground Piping. Any local rules and regulations should also be
consulted along with the recommendations of the pipe manufacturer.
When unstable bedding is encountered and the bottom of the trench is not sufficiently stable
or firm, proper bedding must be installed to prevent vertical or lateral displacement of the
pipe after installation.
Civil Engineering
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Practice 670 210 1200
Publication Date 20Sep95
Page 6 of 6
FLUOR DANIEL
OUTSIDE UNDERGROUND PIPING
Excavate native soil below grade of bedding material and replace with a layer of gravel,
crushed rock, sand, or other coarse aggregate which may produce the desired stability.
Bedding details will be as shown on the drawings.
PIPE
SETTLEMENT
Differential settlement of manholes and connecting sewers can sometimes break the sewer
pipe. A pipe joint just outside the manhole can lessen this danger. If the soil conditions are
unstable or a high water table could leach sand bedding out from under the pipe, a second
joint within 3 feet of the first should be provided. The pipe joints must be flexible such as a
compression or mechanical joint.
Differential settlement of cooling water branch lines and exchangers on piled foundation
which may not settle, can over stress the piping. This problem can be remedied by locating
the headers so that the branch lines are at least 10 feet long and providing flexible
connectors, such as Dresser and Smith-Blair, at either end of the branch of steel pipe, or
using mechanical joints for cast iron pipe.
REFERENCES
Civil Engineering
Practice 670.210.1160:
Sanitary Sewer Systems
Civil Engineering
Practice 670.210.1210:
Loads On Underground Pipe
Civil Engineering
Specification 670.210.02224: Excavation, Backfill, And Compaction For Underground
Piping
Civil Engineering
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For other purposes, refer to the original document
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Practice 670 210 1210
Publication Date 20Sep95
Page 1 of 8
FLUOR DANIEL
LOADS ON UNDERGROUND PIPE
PURPOSE
This practice establishes guidelines for the engineer or designer calculating the loading that
may be expected for various depths of bury and live loads on the surface over underground
pipe and a method to verify that the loading is not excessive. This practice provides a design
methodology to accurately calculate loads on underground pipe. This practice will benefit
engineers and designers when laying out conduits crossings under roads or traffic areas that
could have potentially heavy loading. In most cases, it will be needed to determine the load
produced by the fill and the strength of pipe required to carry the load. In some cases, a
definite strength of pipe will be specified and it will be desired to find a height of fill which
will not produce a load on a pipe greater than that which it is capable of supporting. It is the
responsibility of the engineer or designer to ensure the application of this practice.
SCOPE
This practice provides the following:
Discussion of different types of pipe and the methods for determining the inherent
strength.
Discussion of live and dead loads and the factors affecting the calculations of these
loads.
Description of pipe bedding and the applicable load factors.
A design check and sample calculations.
APPLICATION
It is the responsibility of the engineer and/or designer to consult this practice whenever earth
loads or live loads exceed normal conditions. Normal conditions are defined as normal
depths of bury and normal live loads transmitted by vehicles. This information contained
within this practice would apply to new design as well as checking existing pipes for extreme
loading such as that which would be encountered during construction.
PIPE STRENGTH
When designing underground conduits, inherent pipe strength should be known so the
supporting capability of the pipe is not exceeded by the proposed earth and live loads.
Pipe strengths can be obtained from formulas derived using specific tests or are usually
obtained from pipe manufacturers catalogs.
ASTM (American Society for Testing and Materials) testing standards usually require pipe
strengths to be such that normally expected live and dead loads can be handled. However,
some conditions such as extraordinary loads or very deep or shallow depths of bury require
special attention.
Pipe is normally classified as either rigid or flexible. Rigid pipe such as cast iron, concrete,
or clay fail when the combined load (internal pressure and external load) imposed on them
become greater than their inherent circumferential stiffness and they crack or rupture.
Civil Engineering
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Practice 670 210 1210
Publication Date 20Sep95
Page 2 of 8
FLUOR DANIEL
LOADS ON UNDERGROUND PIPE
Methods Of Testing And
Specifying Pipe Strengths
3 Edge Bearing Strength
(Clay Pipe, Asbestos
Cement Pipe)
The strength of a rigid conduit is normally specified by its resistance in a laboratory test
called the 3 Edge Bearing Test. Since the load is applied to only 3 points on the pipe, the
test is more severe than actual field conditions. To convert the 3 edge bearing strength to the
design or safe supporting strength, multiply by a load factor based on the type of bedding
used, then divide the results by the appropriate safety factor.
D Load Strength
(Concrete Pipe)
For reinforced concrete pipe only, laboratory strength may be expressed as the load per foot
of pipe which causes the pipe to develop an 0.01 inch crack or also as the ultimate load the
pipe will withstand. The strength of the pipe, at either the 0.01 inch crack or ultimate,
divided by the nominal internal diameter of the pipe in feet, is called the D load strength.
For example, a 48 inch diameter reinforced concrete pipe has a 3 edge bearing test load at
0.01 inch crack of 8,000 lb/ft and an ultimate strength of 12,000 lb/ft The 0.01 inch crack
strength is then 2,000D and the ultimate strength is 3,000D.
Ring Test Crushing Load
(Cast Iron Pipe)
The crushing load for cast iron pipe varies with the size and wall thickness of the pipe and
must be calculated. The modulus of rupture which governs the maximum crushing load
should be figured as 40,000 psi; although, pipe having a modulus of rupture of 45,000 psi is
available. The crushing load will decrease with an increase in internal pressure.
Flexible Pipe Strength
Load (Steel Pipe)
Flexible pipe such as steel and plastic combine their own strength with the lateral support of
the compacted soil at the side fills to resist deflection. The maximum external load to be
applied to a flexible pipe is the load that will give a deflection of greater than:
5 percent of the nominal diameter for flexible coating.
2 percent of the nominal diameter for rigid coating.
Internal pressure assists flexible pipe in supporting external loads but cannot be relied on
since the pressure could be shut down.
The table in Attachment 01 has been developed using various ASTM testing methods for
various pipe categories.
Civil Engineering
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Practice 670 210 1210
Publication Date 20Sep95
Page 3 of 8
FLUOR DANIEL
LOADS ON UNDERGROUND PIPE
TYPES OF BURY
Types of bury are essentially classified as that in cut or that in fill. Pipes in a cut situation
are referred to as trench condition and pipes in a fill situation are referred to as embankment
condition. There can also be a combination of both. Refer to Attachment 02.
To simplify this practice and to induce a certain amount of conservatism, this practice will be
limited to trench conditions and embankment conditions. A combination condition will be
considered as an embankment condition.
PIPE LOADING
Formulas and charts for determining loads on an underground pipe are determined from
theories developed by A. Marston, Iowa State University. Earth loads and live or transmitted
loads must be considered when designing underground conduits. Data on live and dead
loads can be obtained from many different handbooks available as well as from pipe
manufacturer's guidelines.
Every condition of bury or loading does not have to be checked for failure. In most cases,
pipe loading does not need to be checked. Most underground pipe design regulations require
that pipe be designed for normal depths of bury with normally expected live loads. Certain
conditions should be checked for pipe loading conditions. These conditions can be the
following:
Depths of bury exceeding 10 feet
Abnormal soil conditions
Unusually high live or transmitted loads
Live loads for depths or buy less than 3 feet
Earth Loads
The amount of earth loads that is transmitted to the pipe is dependent on many factors. The
primary factors that determine earth loading are:
Depth of cover
Width of trench at top of pipe
Rigid or flexible pipe
Type of construction (trench or embankment)
Soil density and cohesion characteristics
Formulas and charts developed by A. Marston provide a means to closely calculate the earth
loading for the variable factors listed above. This data can be found in many available
handbooks. AWWA (American Water Works Association) C-101, is a good example, as
well as many catalogs and handbooks published by pipe manufacturers. Full descriptions of
the various construction conditions are also given.
In order to simplify the determination of earth loading, Attachment 03 may be used for
approximate values. Approximate values from the table are satisfactory for the following
reasons:
Depths of cover are usually less than 8 feet.
Civil Engineering
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Practice 670 210 1210
Publication Date 20Sep95
Page 4 of 8
FLUOR DANIEL
LOADS ON UNDERGROUND PIPE
Earth load values for a depth of 8 feet are well below the 3 edge bearing strength of
vitrified clay pipe or reinforced concrete pipe for any properly installed system.
Unless the width of the trench is specified and controlled during construction,
calculating earth loads from Marston's formula would be impractical.
The unit weight of soil used in Attachment 03 is 120 pounds per cubic foot.
Pipes with 12 inch diameter and less are assumed to have a trench width 1 foot wider
than the outside diameter of the pipe. Pipes from 12 inches to 36 inches are assumed to
have a trench width 2 feet wider than the outside diameter of the pipe.
The table in Attachment 03 is intended to be used as a guide in determining earth loads for
underground conduits with normal bury conditions. For unusual bury conditions such as
large diameter pipes or deep pipes, the designer should consult the pipe manufacturer's
catalog for design criteria.
Live Loads
It is usually not necessary to consider live loads except where they are exceedingly large or
where they occur on conduits with very little cover. A few computations under various
conditions will establish the relative importance of live loads in the designers mind.
Trucks or construction equipment moving over the ground surface above underground piping
subject the piping to loads. A certain percentage of the total load, based on depth of cover
and size of pipe, is transmitted to the pipe. If paving is involved, flexible pavement will
transfer more load to the pipe; whereas, rigid pavement such as concrete will tend to bridge
the pipe transmitting more load to the surrounding soil. For calculating transmitted loads,
use the guidelines that follow and the Table in Attachment 04 which gives the percent of live
load that is transmitted to the pipe for various depths of cover.
For piping under roads, depth of cover should be based on rough grade elevations for the
road, since underground lines will be subject to truck traffic before any asphalt surface is
applied.
For design purposes, use a wheel load of 32,000 pounds (1/2 axle load of 64,000
pounds). The wheel load may be on dual tires but is still considered 1 wheel. This load
is the heaviest that would be expected from a large unladen truck crane. Heavier loads
could be possible during equipment handling or lifting activities and this point should be
reviewed with Construction Management. Generally, the pipe is protected with timber
mats or omitted entirely during these operations.
The wheel load of 32,000 pounds recommended above is twice that of H-20 truck
loading which is used as a basis for bridge and highway design.
Where loads are known to be less or greater, the calculations should be based on the
actual figures. The minimum wheel load used for design purposes is 16,000 pounds
which is normal H-20 loading.
When expecting heavy 1 time construction or equipment loads, the conduit could be
installed after the loading has been imposed.
PIPE BEDDING
The pipe bedding determines the load factor or number to multiply the 3 edge bearing
strength to determine the field supporting strength. The bedding is the contact between the
Civil Engineering
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Practice 670 210 1210
Publication Date 20Sep95
Page 5 of 8
FLUOR DANIEL
LOADS ON UNDERGROUND PIPE
pipe and the foundation on which it rests. The soil on the sides of the pipe and above it is
the backfill. The field supporting strength of a rigid pipe and, therefore, the load factor for a
particular conduit, depend chiefly upon 2 characteristics of the installation as follows:
Width of the bedding of the pipe and the quality of the contact between the pipe and
bedding as it affects the distribution of the vertical forces.
Magnitude of the lateral pressure acting against the sides of the pipe and the area of the
pipe over which the lateral pressure acts.
Cohesion for trench conduits is assumed to be negligible because of the following:
Considerable time must elapse before effective cohesion between the backfill material
and the sides of the trench can develop.
The assumption of no cohesion yields the maximum probable load on the conduit.
Pipe Bedding Classes
Pipe bedding generally falls into 4 classes. These 4 classes are described below.
Class A Load Factor 3.4
This method of bedding involves either a reinforced 2,000 psi concrete cradle or arch. The
concrete will extend to the springline, which is halfway up the side of the pipe. The cross
sectional area ratio of steel to concrete should be 0.4 percent. If no reinforcing is used then
the load factor will be reduced to 2.4. If p = 1.0 percent for concrete arches, then the load
factor can be increased to 4.8.
Class B Load Factor 1.9
This method of bedding involves well graded crushed stone carefully placed and shaped to
the bottom of the pipe with a minimum thickness below the pipe of 4 inches. The bedding
will extend up the haunches to the springline of the pipe with select material as initial
backfill.
Class C Load Factor 1.5
This method of bedding involves carefully placed and compacted material with a wide range
of gradation and possibly locally obtained. The bedding generally extends from 4 inches
below the pipe up to 1/6 of the OD of the pipe. Select backfill will be used as initial backfill.
Class D Load Factor 1.1
This method of bedding involves little or no care when shaping the foundation surface to fit
the lower part of the conduit exterior or to fill all spaces under and around the conduit with
granular materials. Initial backfill will be of select material.
It can be seen by the bedding classes described above that the better quality bedding provides
a higher load factor and, therefore, more load carrying capability.
The economy of the different types of bedding along with the potential live and dead loads
must be taken into account when specifying bedding requirements.
In order to simplify the selection of an appropriate load factor, use a conservative value of
1.5 which is based on ordinary bedding. In special and unusual situations where a line is run
excessively deep (over 10 feet), or for other reasons, it becomes necessary to specify a
Civil Engineering
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Practice 670 210 1210
Publication Date 20Sep95
Page 6 of 8
FLUOR DANIEL
LOADS ON UNDERGROUND PIPE
particular bedding condition, then the appropriate design handbook listed in Attachment 05
should be consulted.
FACTOR OF SAFETY
When the materials are analyzed and the job is properly assembled in the designer's mind, a
factor of safety should be applied to the plans to account the unforeseen stresses which may
be imposed on the structure. This technical practice would not be complete without a
discussion of this factor of safety as applied to the structural design of an underground
conduit. A factor of safety cannot be computed by laws and equations, but depends entirely
upon the judgment and experience of the engineer and/or designer. In general, the Factor of
Safety will range from 1.0 to 1.5 depending on a variety of conditions or situations. Culvert
or nonpressure conduit failures are gradual in occurrence; whereas, pressure conduits usually
fail quickly once a crack develops. Bedding and backfill is another variable factor that must
be considered when selecting a factor of safety. Rigid pipes usually require a higher factor of
safety than flexible pipes since flexible conduits will usually deflect more before they reach
failure.
DESIGN CHECK
This section gives the procedure for checking if a line under a given earth cover, subject to
construction traffic loads, will not be excessively loaded.
Minimum cover for protection against traffic loads
Minimum cover depth which is measured from grade to top of pipe is determined by
computing total load on pipe, but in no case should be less than:
- 2'- 6" for cast iron and asbestos cement pressure lines
- 2'- 0" for steel and concrete pressure lines
- 2'- 0" for all nonpressure lines
Bedding conditions
Where calculations indicate that pipe will not sustain loads at the covers specified above,
consideration may be given to improving the load carrying capability of the pipe by
specifying a bedding condition with a higher load factor.
Formulas and table
- Earth loads (dead loads)
We =
Earth load based on maximum conditions of trench width and
120 lb./cu. foot soil material using Marston formula. Refer to
Attachment 03.
- Truck loads (live loads)
Wt =
Truck load, based on a concentrated wheel load of 32,000 pounds and
an impact factor of 1.0. Use Table in Attachment 04 to determine load
reaching pipe.
If impact factor is required, multiply result by appropriate factor.
Civil Engineering
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Practice 670 210 1210
Publication Date 20Sep95
Page 7 of 8
FLUOR DANIEL
LOADS ON UNDERGROUND PIPE
Safety supporting strength rigid pipe - no pressure.
Safety supporting strength =
3 edge bearing strength x load factor
safety factor
Refer to pipe bedding for load factors.
Safety factors - nonpressure systems:
Clay pipe
Cast iron pipe
Concrete pipe
1.5
1.5
1.0
Safe supporting strength must be equal to, or greater than, We and Wt.
Safety supporting strength rigid pipe, pressure systems.
Since there is a relationship between the amount of load a rigid pipe can carry and the
internal pressure it is subjected to, it is necessary to include the effects of pressure in the
equation to determine maximum load that can be applied. The following may be used for
cast iron pressure pipe:
Wd =
W
P1 − p
P1
where:
Wd
W
P'
p
=
=
=
=
Safe supporting strength (pound)
Crushing load with no internal pressure (pound per linear feet)
Bursting pressure with no external load
Working pressure times 2.5 safety factor
The values of W and P are calculated as follows:
W=
Rt 2
.0795(d + t)
P 1 = 2St
d
where:
R
S
t
d
=
=
=
=
Ring modulus of rupture, use 40,000 psi
Bursting tensile strength, use 18,000 psi
Net thickness (inch) specified thickness less casting tolerance
Nominal pipe size (inch)
Wd must be equal to or greater than:
2.5(We + Wt)
Lf
where:
We
Wt
Lf
=
=
=
Earth load
Truck load
Load factor
Civil Engineering
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Practice 670 210 1210
Publication Date 20Sep95
Page 8 of 8
FLUOR DANIEL
LOADS ON UNDERGROUND PIPE
Safety factor is included in equations.
Safe supporting strength - flexible (steel) pipe.
The deflection determined by the following equation should not exceed the following:
Five percent of nominal pipe diameter for flexible coatings.
Two percent of nominal pipe diameter for rigid coatings.
d=
fK W1 r 3
Et 3 + 732r 3
where:
d
f
W1
=
=
=
E
K
t
=
=
=
ultimate long time deflection of pipe (inches)
1.5 (deflection lag factor)
We + Wt times 1.25 safety factor (pounds/linear feet) r=radius of pipe
(inches)
30,000,000 psi (modulus of elasticity, steel pipe)
Bedding Factor = 0.10
thickness of pipe wall (inches)
ATTACHMENTS
Attachment 01: (20Sep95)
Crushing Strength
Attachment 02:
Types Of Bury
Attachment 03: (20Sep95)
Dead Load From Earth Cover On Underground Pipes
Attachment 04: (20Sep95)
Percentage Of Wheel Load Transmitted To Underground Pipe
Attachment 05: (20Sep95)
Design Handbook Listing
Attachment 06:
Sample Design 1
Civil Engineering
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Practice 670 210 1210
Publication Date 20Sep95
Attachment 01 Page 1 of 1
FLUOR DANIEL
CRUSHING STRENGTH
(3-Edge Bearing Test, Lbs. Per Ln. Ft.)
Pipe Size
(in.)
Vitrified Clay Nonreinforced C.I. Soil Pipe
Extra Strength Concrete Class Extra Heavy
ASTM C-700 2 ASTM C-14 ASTM A-74
Reinforced Concrete, ASTM C-76
Load to Produce a .01" Crack
Class II
Class III
Class IV
Class V
4
2,000
2,000
6,500
6
2,000
2,000
4,400
8
2,200
2,000
4,275
10
2,400
2,000
4,275
12
2,600
2,250
4,425
1,000
1,350
2,000
3,000
15
2,900
2,600
5,310
1,250
1,688
2,500
3,750
18
3,300
3,000
1,500
2,025
3,000
4,500
21
3,850
3,300
1,750
2,363
3,500
5,250
24
4,400
3,600
2,000
2,700
4,000
6,000
27
4,700
2,250
3,038
4,500
6,750
30
5,000
2,500
3,375
5,000
7,500
33
5,500
2,750
3,713
5,500
8,250
36
6,000
3,000
4,050
6,000
9,000
Civil Engineering
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Practice 670 210 1210
Publication Date 20Sep95
Attachment 03 Page 1 of 1
FLUOR DANIEL
DEAD LOAD FROM EARTH COVER ON UNDERGROUND PIPES
(Loads are Shown in Lbs. Per Ln. Ft. of Pipe)
Depth of
Cover,
Ft.
Nominal Pipe Diameter, Inch.
4
6
8
10
12
15
18
21
24
27
30
33
36
2
180
240
290
340
390
450
500
560
610
700
750
820
875
3
270
370
460
550
630
750
860
950
1,040
1,120
1,200
1,300
1,400
4
370
520
650
780
920
1,080
1,230
1,400
1,520
1,630
1,750
1,850
2,000
5
470
660
830
1,000
1,160
1,420
1,610
1,810
2,010
2,200
2,340
2,500
2,630
6
570
800
1,000
1,200
1,430
1,710
2,000
2,230
2,500
2,700
2,950
3,180
3,350
7
670
950
1,180
1,420
1,700
2,050
2,400
2,700
3,050
3,300
3,570
3,900
4,100
8
780
1,080
1,370
1,620
1,960
2,400
2,780
3,200
3,550
3,900
4,200
4,500
4,800
Civil Engineering
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Practice 670 210 1210
Publication Date 20Sep95
Attachment 04 Page 1 of 1
FLUOR DANIEL
PERCENTAGE OF WHEEL LOADS TRANSMITTED TO UNDERGROUND PIPES
(Figures Show Percentage of Wheel Load Applied to One Ln. Ft. of Pipe)
Depth of
Cover,
Ft.
Nominal Pipe Diameter, Inches
4
6
8
10
12
15
18
21
24
27
30
33
36
1
9.3
12.8
15
17.3
20
22.6
24.8
26.4
27.2
28
28.6
29
29.4
2
4.3
5.7
7
8.3
9.6
11.5
13.2
15
15.6
16.8
17.8
18.7
19.5
3
2
2.9
3.6
4.3
5.2
6.4
7.5
8.6
9.3
10.2
11.1
11.8
12.5
4
1.2
1.7
2.1
2.5
3.1
3..9
4.6
5.3
5.8
6.5
7.2
7.9
8.5
5
0.7
1.2
1.4
1.7
2.1
2.6
3.1
3.6
3.9
4.4
4.9
5.3
5.8
6
0.5
0.8
1
1.1
1.4
1.8
2.1
2.5
2.8
3.1
3.5
3.8
4.2
7
0.2
0.5
0.7
0.8
1
1.3
1.6
1.3
2.1
2.3
2.6
2.9
3.2
8
0.1
0.4
0.5
0.6
0.8
1
1.2
1.4
1.6
1.8
2
2.2
2.3
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Practice 670 210 1210
Publication Date 20Sep95
Attachment 05 Page 1 of 1
FLUOR DANIEL
DESIGN HANDBOOK LISTING
Pipe
Handbook
Publisher
Asbestos Cement
Standard Practice for the Selection
of Asbestos Cement Water Pipe
AWWA
Cast Iron
Thickness Design of Cast Iron
Pipe
AWWA
Concrete Sewer
Concrete Pipe Handbook
American Concrete Pipe
Association
Steel
Steel Pipe Design and Installation
AWWA
Vitrified Clay
Clay Pipe Engineering Manual
National Clay Pipe Institute
Civil Engineering
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Practice 670 210 1211
Publication Date 20Sep95
Page 1 of 6
FLUOR DANIEL
THRUST RESTRAINT DESIGN
PURPOSE
This practice establishes guidelines for the analysis and design of thrust blocks and joint
restraint for pipelines and underground piping. It is the responsibility of the Civil Lead
Engineer or Designer to utilize this practice where necessary.
SCOPE
This practice includes the following:
Discussions of thrust restraint for pressure piping, including both thrust blocks and pipe
joint restraints.
Typical values for soil parameters.
Thrust values.
APPLICATION
Thrust restraint must be included in the design and construction of pressure piping systems.
Without thrust restraint, piping may separate during service.
THRUST GENERATION
Thrust exists in pressure piping wherever there is a deflection, either horizontally or
vertically, in the line. The thrust forces are generated from the static and dynamic fluid
action on the pipe. Velocities in the majority of lines are of such low magnitude that
dynamic thrust can usually be neglected. However, static thrust in pipes due to internal
pressure usually require some kind of thrust restraint since the forces are of large magnitude.
Large pipe diameters together with large deflection angles and high internal pressure will
cause very large thrust forces that require careful design.
RESTRAINT METHODS
Restraint for unbalanced forces in piping systems may be accomplished using one or a
combination of the following methods:
Concrete thrust blocks
Restrained joints
Thrust Blocks
Thrust blocks are cast in place concrete blocks designed to transmit unbalanced forces from
the pipe fitting to the soil that the block bears against. A thrust block acts similar to a spread
footing, distributing the thrust across an adequate area of undisturbed soil. Thrust blocks
must be cast in place against undisturbed soil which is very important in the selection of a
thrust restraint system. Future excavation will disturb the soil bearing area in congested
utility areas. Also, past excavation in a given area may not allow for thrust blocks to be
utilized in such a case.
Civil Engineering
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Practice 670 210 1211
Publication Date 20Sep95
Page 2 of 6
FLUOR DANIEL
THRUST RESTRAINT DESIGN
Other considerations that must be addressed in the selection phase of a thrust restraint
system is available space, soil parameters, and whether the deflection is vertical or
horizontal. A crowded utility corridor or small plant area may cause the design of a thrust
block to be impractical because of space and excavation limitations. Also poor soil bearing
capacities may require thrust blocks to become too large for the available space. Thrust
blocks should not be used for vertical thrust restraint hat is in the upward direction.
Downward vertical and horizontal thrusts are appropriate directions for thrust block
restraint.
Location
Location of thrust blocks:
Horizontal deflections greater than 10 degrees
Downward vertical deflections
Under valves in asbestos cement systems (not used much anymore)
At fire hydrants
The direction of thrust and the direction of the soil resultant reaction must be collinear to
prevent an unbalanced moment from acting on the system. The depth to the bottom of the
thrust block from the soil surface should be equal to or greater than two times the height of
the block.
Sizing
Sizing of thrust blocks, as with all thrust restraint systems, must be designed for the highest
pressure the pipe will experience throughout its service life. Typically, the highest pressure
will occur during testing of the pipe line.
Calculation of thrust resulting from pipe deflection is determined using the following
formula:
T = 2PASin  Θ 
2
Equation 1
where:
T
P
A
Θ
=
=
=
=
Thrust (pounds
Maximum (Test) Pressure psi
Cross Sectional Area (Square Inch) of pipe
Pipe Deflection
Values calculated from the above formula have no factor of safety.
Values of thrust forces have been tabulated by the CIPRA (Cast Iron Pipe Research
Association) and are presented in Attachment 01, Table 1. Values in Attachment 01,
Table 1 are higher than those calculated using Equation 1. CIPRA values may contain a
factor of safety that has been included in these values.
As stated above, thrust blocks will be sized on the basis of test pressure in accordance with
Attachment 01, Table 1, or the calculated value, and the bearing capacities of the soil.
Bearing capacities are readily available from the project soils report. For preliminary sizing,
Civil Engineering
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Publication Date 20Sep95
Page 3 of 6
FLUOR DANIEL
THRUST RESTRAINT DESIGN
Attachment 01, Table 2 shows typical soil classifications with bearing capacities. Again,
these values should only be used for preliminary sizing of blocks.
Knowing the force and soil bearing capacities, the thrust block size can be calculated. Block
width usually varies from one to two times the height. Again, the height of the block should
be at least as high as the outside pipe diameter and at least as deep as the block is high.
Reinforcement placement, sizing, and spacing for large blocks should be reviewed by
structural engineering for adequacy.
The placement of thrust blocks should be at a 45 degree angle to the soil bearing surface and
should not cover any bolts or fittings of the piping.
Restrained Joints
Restrained joints are specially designed joints that together with soil friction transfer forces
at pipe bends. Restrained joints are predominantly used where thrust blocks are not
economical or practical due to limited space, access, unstable soils, or possible disturbance
by future excavation.
When restrained joints are used, the pipeline becomes its own thrust block. By restraining a
length of pipe near bends and along the pipe line, the thrust force is transferred to the
surrounding soil by the pipe.
Unbalanced Forces
Horizontal Bends:
The length of pipe to be restrained is calculated by the formula
L=
S f PAK
KF s + DP p
Equation 2
where:
L
Sf
P
A
Fs
Θ
=
=
=
=
=
=
K
=
Pp
D
=
=
length of pipe to be restrained (feet)
safety factor
internal pressure (psi)
cross sectional pipe area (square inch)
pipe to soil friction (pounds per feet)
deflection angle
4 tan  Θ 
2
passive soil resistance (psf)
pipe diameter (feet)
The length (L) calculated specifies the length of pipe that is required to be fitted with
restrained joints to prevent the pipes from separating. Within this length, frictional and
bearing forces of the soil will resist the thrust forces imposed from the pipe line deflection.
To calculate pipe to soil friction, Fs, certain soil parameters are required.
Fs = Ap C + W tan δ
Civil Engineering
This copy is intended for use solely with
Piping Design Layout Training.
For other purposes, refer to the original document
available through Knowledge Online.
Practice 670 210 1211
Publication Date 20Sep95
Page 4 of 6
FLUOR DANIEL
THRUST RESTRAINT DESIGN
where:
Ap
C
W
δ
φ
fφ
=
=
=
=
=
=
pipe surface area (SF/LF)
pipe cohesion (psf)
normal force on pipe (plf)
fφφ
soil internal friction angle (degree)
pipe friction to soil friction ratio
Also:
C
= fc Cs
where:
fc
Cs
=
=
pipe cohesion to soil cohesion ratio
soil cohesion (psf)
Typical values of soil parameters are presented in Attachment 02, Soil Friction and Cohesion
Factor, from Thrust Restraint For Underground Piping Systems by R. J. Carlsem. The soil
parameters to be used for the friction calculation should be for whatever soil is in direct
contact with the pipe. For example, if the pipe is surrounded by bedding material and the
trench then backfilled with native material, the bedding parameters should be used for the
calculations.
To calculate the normal force on the pipe (W), the weight of the pipe plus the weight of fluid
in the pipe plus the weight of soil above the pipe are added together. The soil above the pipe
may be simplified to:
We = ω HD
where:
We
ω
H
D
=
=
=
=
weight of earth (plf)
unit weight of soil (pcf)
depth of cover (feet)
pipe diameter (feet)
The passive soil resistance, Pp, is calculated using Rankine Theory.
P p = ωH c N φ + 2C s N φ
where:
Hc
Nφ
=
=
height of cover (feet)
φ
tan2  45 o + 2 
To accurately account for all forces along the pipe length, an additional force for the added
resistance resulting from pipe bells should be added to Fs to calculate F's.
F's = Fs + Fb
Civil Engineering
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For other purposes, refer to the original document
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Practice 670 210 1211
Publication Date 20Sep95
Page 5 of 6
FLUOR DANIEL
THRUST RESTRAINT DESIGN
where
Fb
=
Db
D
=
=
π
P p  D 2b − D 2 
4
outside diameter of bell (feet)
diameter of pipe (feet)
If the pipe is to be wrapped or encased with polyethylene, the value of Fs and F's must be
reduced by 30 percent to account for slipping which may occur between the pipe and
polyethylene.
Vertical Bends:
For unbalanced forces resulting in vertical uplift the following formula should be
incorporated for design lengths:
L=
S f KPA
KF s + 2W
Terms have been previously defined.
Dead Ends:
The required length for unbalanced forces resulting from a dead end is calculated as follows:
L=
S f PA
Fs
Passive soil resistance may be included if the soil is to remain undisturbed.
Tees
Tees in pipe line are capable of restraining quite a lot of force through passive soil
resistance.
L=
S f (4PA − DP p L x )
4F s
where:
Ls
LT
=
=
LT + 2Lp
length of tee (feet)
Lp
=
length of pipe adjacent to fitting (feet)
General
When designing thrust restraint joints, one problem to be aware of is restraint length overlap
and bend combinations. If two deflections are located near one another, the total deflection
to be designed for may be the sum of the two deflections if bends are within each others
restraint length. Also, joints should always be designed for test pressures if that is the
maximum pressure that the pipe will experience.
Civil Engineering
This copy is intended for use solely with
Piping Design Layout Training.
For other purposes, refer to the original document
available through Knowledge Online.
Practice 670 210 1211
Publication Date 20Sep95
Page 6 of 6
FLUOR DANIEL
THRUST RESTRAINT DESIGN
REFERENCES
Carlsem, Roger J. Thrust Restraint for Underground Piping Systems. CIPRA (Cast Iron
Pipe Research Association).
Handbook - Ductile Iron and Cast Iron Pipe. Cast Iron Pipe Research Association. Oak
Brook, Illinois.
Kennedy, H., D.S. Shumard, C.M. Meeks. Ductile Iron Pipe Thrust Restraint Design
Handbook. EBAA Iron Sales, Eastland, Texas.
ATTACHMENTS
Attachment 01: (20Sep95)
Table 1.
Thrust at Fittings in lbs/100 psi Water Pressure
Table 2.
Approximate Values of Soil Capacities for Preliminary Design
Attachment 02: (20Sep95)
Soil Friction and Cohesion Factor
Civil Engineering
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For other purposes, refer to the original document
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Practice 670 210 1211
Publication Date 20Sep95
Attachment 01 Page 1 of 1
FLUOR DANIEL
THRUST RESTRAINT DESIGN
Table 1. Thrust At Fittings In lbs/100 psi Water Pressure
Pipe Size
Inches
Pipe End or
Tee
90 Degree
Bend
45 Degree
Bend
22.5 Degree 11.25 Degree
Bend
Bend
4
1,810
2,559
1,385
706
355
6
3,739
5,288
2,862
1,459
733
8
6,433
9,097
4,923
2,510
1,261
10
9,677
13,685
7,406
3,776
1,897
12
13,685
19,353
10,474
5,340
2,683
14
18,385
26,001
14,072
7,174
3,604
16
23,779
33,628
18,199
9,278
4,661
18
29,865
42,235
22,858
11,653
5,855
20
36,644
51,822
28,046
14,298
7,183
24
52,279
73,934
40,013
20,398
10,249
30
80,425
113,738
61,554
31,380
15,766
Note!!! To determine thrust at pressures other than 100 psi, multiply the thrust obtained in the table by the ratio of
pressure to 100.
For example, the thrusts on a 12 inch, 90 degree bend at 125 psi is
19, 353 x
125
100
= 24, 191 pounds
Carlsem, Roger J. Thrust Restraint for Underground Piping Systems. CIPRA
Table 2. Approximate Values of Soil Capacities for Preliminary Design.
Type of Soil
Muck, peat, etc.
Safe Load lbs/SF
0
Soft Clay
1,000
Sandy Silt
3,000
Sand
4,000
Sandy Clay
6,000
Civil Engineering
Practice 670 210 1211
Publication Date 20Sep95
Attachment 02 Page 1 of 1
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FLUOR DANIEL
SOIL FRICTION AND COHESION FACTOR
Soil Description
Friction Angle
Degrees
Cohesion Cs (psf)
fφ
fc
44.5
39
0
0
0.76
0.80
0
0
40
32
0
0
0.95
0.75
0
0
13 - 22
385 - 920
0.65
0.35
11.5 - 16.5
460 - 1,175
0.50
0.50
0.50
0.80
Well Graded Sand:
Dry
Saturated
Silt (Passing No. 200):
Dry
Saturated
Cohesive Granular:
Wet to Moist
Clay:
Wet to Moist
At Max. Compact
Civil Engineering
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Practice 000 250 2040
Date 11Feb00
Page 1 of 5
PLANT ARRANGEMENT - TYPICAL UNIT PLOT ARRANGEMENT
PURPOSE
This practice establishes recommended guidelines to assist the Piping Designer for
development of a unit plot arrangement.
SCOPE
This practice is arranged in the following major sections:
•
RESPONSIBILITY
•
ARRANGEMENT OF EQUIPMENT
•
EQUIPMENT AND PIPEWAY CLEARANCES
•
PIPEWAY LAYOUT
•
REFERENCES
•
ATTACHMENTS
APPLICATION
This practice is to be used as a guideline for the development of the unit Plot Plan.
RESPONSIBILITY
It is the Lead Piping Supervisor's responsibility to ensure that this guideline is
followed, along with any specific client requirements.
ARRANGEMENT OF
EQUIPMENT
Note!!! The numbers enclosed in parentheses below refer to specific notes in circles
on Attachments 01, 02, and 03.
Equipment Structures
The plant layout of equipment shall utilize common structures for equipment vessels
and pumps. As a rule single installation of equipment will not require a structure.
Vertical Vessels
Vertical vessels (A1) will be on a given centerline established by the largest vessel.
The shell of the largest vessel will be 2'- 0" from the aisleway reference line.
Vessels that are considered larger than the average vessel (A1.1) in a unit, will be
established independently with the shell located 2'- 0" from the aisleway reference
line.
Manways in vertical vessels will normally be located on the side of the vessel away
from the pipe rack. This leaves the pipe rack side clear for pipes going to and from
the rack. Ladders will be located on either side of the vessel.
/0002502040.doc
Piping Engineering
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Practice 000 250 2040
Date 11Feb00
Page 2 of 5
PLANT ARRANGEMENT - TYPICAL UNIT PLOT ARRANGEMENT
Stacking two or more vertical vessels shall be investigated. This investigation shall
consider the process conditions (commodities, temperatures, pressures), vertical
height limitations, and piping layout for economic advantages. The stacking of
vessels requires the acceptance of Process and Vessel engineering.
Horizontal
Vessels
Horizontal vessels (A2) will have the head of the largest vessel line up with the
aisleway reference line. All other horizontal vessels in the same vicinity will have a
common tangent line coordinate with the largest vessel. It may be economical for
adjacent vessels to share a common saddle coordinate to utilize a common
foundation.
The minimum elevation from grade is usually shown on the P&ID if it is critical for
process reasons. If no elevation is expressed and minimum is required, care should
be taken to allow adequate clearance for piping.
Exchangers
Shell and tube heat exchangers (A3.1) will be lined up with their channel heads away
from the pipeways, so that tube withdrawal is toward the outside of the unit.
The shell heads will be lined up so that the largest head is in line with the aisleway
reference line. All other exchangers are to be lined up to have a common channel
nozzle coordinate. It may be economical for adjacent exchangers to share a common
saddle coordinate to utilize a common foundation.
"G"- fin or fin tube type exchangers will be located (A3.2) with the centerline of the
shell nozzles lined up and located such that all piping remains clear of the aisleway
reference line.
Horizontal reboilers (A3.3) will preferably be located next to the equipment they
service.
Pumps
Locate pumps close to the equipment from which they take suction (A4.1). Pumps
handling flammable products are not to be located under pipeways carrying major
product lines, air coolers, or vessels. Pumps handling non-flammable products may
be located under pipeways and air cooled exchangers.
Pumps located between pipeways and equipment row should be located to avoid
being hazardous to pipeway and equipment. Industrial Risk Insurers IM.2.5.2 (IRI)
indicates the minimum distance to be 10 feet clear (A4.2); this distance should be
verified by the clients requirements.
Layout pump suctions and discharges on common centerlines, allowing the use of
common pipe supports (A4.3).
Aircoolers
Aircoolers will normally be located above the pipeways (A5).
/0002502040.doc
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Practice 000 250 2040
Date 11Feb00
Page 3 of 5
PLANT ARRANGEMENT - TYPICAL UNIT PLOT ARRANGEMENT
Furnaces
Furnaces should be located upwind or sidewind from the rest of the unit and be
separated by at least 50 feet.
Compressors
Compressors should be located downwind from the rest of the unit, be separated
from the other equipment, and preferably not located in an enclosed building.
Valve Manifolds
Operational valve manifolds, control valve manifolds and utility stations (A6) are to
be located for operability and access.
EQUIPMENT AND
PIPEWAY CLEARANCES
Walkways
2'- 6" horizontal by 7'- 0" vertical (C1.1).
Aisleway
For forklift or similar equipment 6'- 0" horizontal by 8'- 0" vertical. For portable
manual equipment operation 3'- 0" horizontal by 8'- 0" vertical (C1.2).
Access Way
Mobil equipment access (hydraulic cranes, trucks, etc.) 10'- 0" horizontal by 10'- 0"
vertical (C1.3).
Flange Clearance
Between adjacent equipment (example: shell and tube heat exchangers) 1'- 6"
clearance between flanges if no other access is required (C2).
Foundation Footings
Minimum (2'- 6") walkway clearances are required between foundations of any
equipment and any adjacent equipment or piping.
Pump Clearances
For pumps extending under the pipeways, a minimum 10'- 0" (C4.1) clearance is
required between pumps at opposite sides of the rack. This clearance need not be in
a straight line down a series of pumps under the rack.
Minimum clearance of 3'- 0" is required between pumps (C4.2). The 3'- 0"
dimension is a minimum requirement between adjacent equipment, foundation or
piping.
/0002502040.doc
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Practice 000 250 2040
Date 11Feb00
Page 4 of 5
PLANT ARRANGEMENT - TYPICAL UNIT PLOT ARRANGEMENT
Exchanger Clearances
Clear aisleway for exchanger shell head removal will be 6'- 0" when using a fork lift
truck or portable "A" frame (C4.3).
3'- 0" clear platform is required when using a mobile crane positioned at channel end
to remove shell cover (C4.3.1).
3'- 0" clear when shell cover is fixed and removal is not required.
Miscellaneous Clearances
Platforms will be 1'- 0" minimum clear of piping or pipeway (C4.4.1). Allow
clearance for drain funnels in front of pumps (C4.4.2).
Road Clearances
The requirements for drainage ditches or underground pipeway easement may
increase the dimension from the edge of roads to equipment (C5).
PIPEWAY LAYOUT
For pipeway support elevations (P1), refer to Practice 000.250.2041: Plant
Arrangement - Pipeway Layout - Allowable Pipe Spans.
•
Pipe support spacings shall be maximized using the limits of pipe spans and
structural integrity.
Location of electrical and instrument raceways will be determined by one of the
following:
•
When electrical is located primarily aboveground (P2.1), raceways for electrical
and instruments will be located as shown (vertical or horizontal, with horizontal
being the alternate location), taking care not to interfere with pipe turn-outs and
expansion loops.
•
On projects where electrical is predominately aboveground, the top level of the
pipeway (P2.2) will be reserved for electrical and instrument raceways.
Drop space (P3), if required, for utility, steam trap, or vent piping drop space width
is set by minimum clearance for largest line and may be on either or both sides of
pipeway as required.
The centerline of line drops (P4) will normally be 2'- 0" from centerline of P.S.
column or end of cantilever, whichever is applicable. Special consideration needs to
be given to large diameter lines.
Width of rack (P5) will be determined by the flow diagram transposition.
Refer to Practice 000.250.2010: Plant Arrangement - Flow Diagram Transposition
Instructions.
For pipe support spacing (P6), refer to Practice 000.250.2041.
/0002502040.doc
Piping Engineering
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For other purposes, refer to the original document
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Practice 000 250 2040
Date 11Feb00
Page 5 of 5
PLANT ARRANGEMENT - TYPICAL UNIT PLOT ARRANGEMENT
REFERENCES
Piping Engineering
Practice 000.250.2005:
Piping Engineering
Practice 000.250.2010:
Piping Engineering
Practice 000.250.2015:
Piping Engineering
Practice 000.250.2041:
Plant Arrangement - Plot Plan Development
Instructions
Plant Arrangement - Flow Diagram Transposition
Instructions
Plant Arrangement Location Control Plan
Instructions
Plant Arrangement - Pipeway Layout – Allowable
Pipe Spans
ATTACHMENTS
Attachment 01: (11Feb00)
Unit Plot Arrangement
Attachment 02: (11Feb00)
Section Thru Pipeway, Standard Arrangements
Attachment 03: (11Feb00)
Space Allocation At Support Columns
/0002502040.doc
Piping Engineering
This copy is intended for use solely with
Piping Design Layout Training.
For other purposes, refer to the original document
available through Knowledge Online.
This copy is intended for use solely with
Piping Design Layout Training.
For other purposes, refer to the original document
available through Knowledge Online.
This copy is intended for use solely with
Piping Design Layout Training.
For other purposes, refer to the original document
available through Knowledge Online.
Practice 000 250 1938
Date: 10Sept01
Page 1 of 2
This copy is intended for use solely with
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For other purposes, refer to the original document
available through Knowledge Online.
FLUOR DANIEL
WORK INSTRUCTION: UNDERGROUND PIPING PRELIMINARY LAYOUT
Lead Engineer:
Activity
Responsibility
1 Confirm the requirements and scope of Piping Lead Engineer
Engineering's involvement with underground.
Originator
2 Review and provide specific contract
instructions. This review will include (but is not
limited to) the following:
• Project specifications
• Project standards
• Plot plan
• P&IDs (Piping and Instrumentation
Diagrams) and UFDs (Utility Flow
Diagrams)
• Site meteorological and soil report
Note!!! On PDS projects refer to Piping
Engineering Practice 000.250.9106:
Underground Piping Partition
Instructions, as well.
3 Issue the underground piping requirements to
the Piping Design Task Force.
4 Identify the types of underground systems and
segregation required.
5 Select piping material types and classes.
6 Determine extent of paved areas.
7 Determine process drainage rates and
temperatures.
8 Determine firewater capacity and line sizing.
9 Identify equipment and structures requiring
firewater deluge systems.
10 Identify main drainage areas on the plot plan
and route underground headers.
11 Indicate catch basins, drain boxes, drain funnels,
and pipe stubups.
12 Route underground firemains and indicate
location of hydrants, monitors, and isolation
valves.
13 Route all other process and utility underground
piping.
14 Calculate gravity drain header size and slope
requirements.
0002501938.doc
Acceptance
Comment
Criteria
000.101.1250 000.250.0005
000.210.1150
000.210.1160
000.210.1200
000.210.1210
000.210.1211
Design
Supervisor
Originator
Process
Originator
Process
Materials
Materials
Metallurgy
Originator
Process
Originator
Process
Originator
Process
Originator
Process
Originator
000.210.1200
Originator
Originator
Originator
Originator
000.210.1150
000.210.1160
Piping Engineering
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For other purposes, refer to the original document
available through Knowledge Online.
Practice 000 250 1938
Date: 10Sept01
Page 2 of 2
FLUOR DANIEL
WORK INSTRUCTION: UNDERGROUND PIPING PRELIMINARY LAYOUT
15 Review loads on piping and determine depth
and type of bury, protection, and need for thrust
restraints.
16 Identify and allocate major underground piping,
electrical, and instrument cable space
reservations, intersections, and elevations.
17 Self-check.
Obtain required checks and approvals.
18 Issue for information and preliminary MTO
(Material Takeoff).
0002501938.doc
Originator
000.210.1210
000.210.1211
Originator
Electrical
Control Systems
Civil
Originator
000.250.2938
Refer to AP
(Activity Plan)
Design
Supervisor
000.250.0072
000.250.2938
Piping Engineering
This copy is intended for use solely with
Piping Design Layout Training.
For other purposes, refer to the original document
available through Knowledge Online.
Practice 000 250 1939
Date: 10Sept01
Page 1 of 1
FLUOR DANIEL
WORK INSTRUCTION: UNDERGROUND PIPING PLANS
Lead Engineer:
Activity
1 Confirm the requirements and scope of pipings
underground drawing deliverables.
2 Review and provide specific contract
instructions.
3 Issue the underground piping plan requirements
to the Piping Design Task Force.
4 Obtain the following information relevant to the
assigned area:
• Project specifications
• Project standards
• Project piping Practices and design
instructions
• P&ID (Piping and Instrumentation Diagrams)
and UFDs (Utility Flow Diagrams)
• Plot plan
• Concrete foundation drawings or CAD model
files
• Underground cable drawings
• Underground piping layouts
• Adjacent underground drawings
5 Check that underground layout is up-to-date and
that drain funnels and piping stub-ups have been
specified where called for on P&IDs,
aboveground piping plans, and plastic models.
6 Review revisions to original layout for any
effect on hydraulics, line sizing, firewater
coverage, and extent of paving.
7 Prepare underground piping plan in accordance
with project specifications, standards, and
drawing format.
8 Route piping in accordance with layout
drawing, locating and dimensioning piping
mains, catch basins, drain funnels, and piping
stub-ups.
9 Indicate thrust blocks, as required.
10 Self-check.
Obtain required checks and approvals.
11 Send drawing to Material Control for MTO
(Material Takeoff) and B/M (Bill of Material).
12 Issue drawing with B/M in accordance with
project procedures.
0002501939.doc
Responsibility
Lead Engineer
Acceptance
Criteria
000.101.1250
Lead Engineer,
Supervisor
Supervisor
Comment
000.200.1050
Originator
Originator
Originator
Originator
Originator
Originator
Originator
000.250.2939
Refer to AP
(Activity Plan)
000.250.0072
000.250.1037
000.250.1038
000.250.2939
Design
Supervisor
Design
Supervisor
000.200.0220 000.200.0821
Piping Engineering