CE 242- HIGHWAY AND RAILROAD ENGINEERING V. ROADBED CONSTRUCTION Research Work Members: Ruel, Ralp Benzon Sagaral, Hans Christian Saguban, Alvin Sanoy, Arriane Kate June 22, 2023 I. Introduction Roads are vital components of modern transportation systems, providing crucial connectivity for people, goods, and services. A well-constructed roadbed forms the foundation for a reliable and efficient transportation network. The construction of roadbeds involves a comprehensive process that encompasses various engineering principles, materials, and techniques, all aimed at ensuring durability, safety, and sustainability. The purpose of this research paper is to delve into the intricate world of roadbed construction, exploring its key elements, challenges, and advancements. By understanding the fundamental aspects of roadbed construction, we can gain valuable insights into how infrastructure development contributes to economic growth, social mobility, and environmental sustainability. In this paper, we will examine the essential components of roadbed construction, starting with the subgrade, which serves as the support layer beneath the road surface. The subgrade plays a critical role in distributing the load and accommodating the stresses imposed by traffic. We will explore the factors influencing subgrade design, such as soil characteristics, moisture content, and compaction techniques. Furthermore, we will discuss the selection and use of materials in roadbed construction. Various materials, such as aggregates, geotextiles, and stabilization agents, are employed to enhance the strength, stability, and longevity of roadbeds. We will examine the properties and performance characteristics of these materials, as well as their environmental impact and cost-effectiveness. Moreover, this paper will highlight the importance of incorporating sustainable practices in roadbed construction. As the world faces increasing concerns about climate change and environmental degradation, the construction industry must strive to adopt greener approaches. We will explore eco-friendly techniques, such as recycled materials, permeable pavements, and innovative construction methods that minimize carbon emissions and resource consumption. Throughout the paper, we will discuss the challenges and advancements in roadbed construction. We will analyze how technological innovations, such as intelligent compaction, geospatial modeling, and data-driven decision-making, are revolutionizing the field. Additionally, we will address the challenges associated with retrofitting existing roadbeds and adapting to changing environmental conditions. In conclusion, roadbed construction plays a crucial role in establishing a reliable and sustainable transportation network. By comprehensively exploring the various elements of roadbed construction, we can gain a deeper understanding of the engineering principles, materials, and techniques involved. Furthermore, this paper will highlight the importance of embracing sustainable practices and technological advancements to ensure the longevity and resilience of our road infrastructure, thereby facilitating economic growth and improving the overall quality of life. II. Discussion A. What is Roadbed? is a structure onto which the road base course is laid. In road construction, roadbed plays an important role. Depending on whether roadbed is located in a cut or in an embankment, it has its own specific aspects and different structure. B. History of Road Transport • • • • • • The world's oldest known paved road was laid in Egypt sometime between 2600 and 2200 BC. Stone-paved streets are found in the city of Ur in the Middle East dating back to 4000 BC. Corduroy roads (log roads) are found dating to 4000 BC in Glastonbury, England Qasr Dimai- the antic paved road towards lake Qarun Porta Risa-Greek Street dating from the 3rd to 4th century BC in Velta with a paved surface and gutters. Sweet track- timber trackway; one of the oldest engineered roads discovered and the oldest timber trackway discovered in Northern Europe C. Constructing the Roadbed A. Three major structural parts of roadway 1. The Sub-grade or sub-base- is the earth or soil beneath the road, properly arranges and graded, compacted and stabilized. a.Cut Section of Road – the sub-base is the original soil below the layers designated as the base b.) Fill Section of Road – the sub-base consists of transported materials taken from nearby roadway cuts or from borrow pit 2. The Base Coarse – is the materials laid on top of the sub- grade or sub-base consisting of crushed stone or gravel, sometimes mixed with asphalt Binders. 3.The Pavement – is the materials laid over the base coarse base course consisting of Asphalt Concrete or Portland Cement Concrete. D. Types of Base Coarse 1. The granular base coarse or untreated soil mixture- it is a road surface of untreated soil mixture described as gravel road Gravel road- consist largely pebbles or crushed rock particles combined with either, clay, lime, iron oxide or other fine materials sufficient enough to serve as binder of the coarse particle. Construction and Maintenance Requirement of Untreated Gravel Road Surface 1.That the road must be stable to support the supper imposed loads detrimental deformation 2. It must shed the large portion of rain that falls on the surface because water penetrating the sub grade might soften it and loosen the surface stability. 3. It must be free from large rocks or stones over one inch in diameter so that it could be regularly maintained by blading or dragging. 4. Gravel Road must possess capillarity properties sufficient enough to replace the moisture lost through the surface evaporation. 5. On dry weather, the moisture film on the clay particles should bind the entire mass together, and in wet weather the first rain that fall on the surface, should expand the clay and close the pores to prevent water from entering and softening of the materials. 6. An excessive amount of highly expansive materials should be avoided because clay swell and unseat the coarser materials when wet and ultimately will weaken the stability of road. 7. Gravel Road must be low cost. Funds for low traffic road is very limited that most of the time overlooked in the list of appropriation priorities except on election period. 8. Use local materials, those materials that could be found nearby the project 2. Treated base coarse- in order to stabilize the base coarse, it is treated with either asphalt, lime Portland cement or other materials are mixed with the aggregates base coarse 3. Sand and Asphalt Base Coarse- composed of either loose beach sand, dune pit or river sand cemented with asphalt materials. 4. Fine Grain Asphalt Base- is an asphalt stabilized base and sub-grade constructed with fine grained has a controlled Plastic Index of 6 to 10 • Aggregates with plasticity index up to 30 are processed with lime. Those with up to 50% passing the No. 200 sieve and plastic index up to 18 can be stabilized even without pre-treatment 5. Soil and Base Coarse Stabilized with Cement - cement stabilization by mixing natural materials and Portland cement compacted at optimum moisture content and cured to hydrate the cement is considerably strong and stable base. The stabilized cement mixture is called “soil cement” produced by using abundant native local materials subdivided into three parts: a. Sandy, and gravel soils containing less than 25% silt and clay. b. Sand with lesser number of fines like beach sand, clay, glacial and windblown sand. c. Silty and clayey soils E. Grading and Maintenance of Untreated Surface The cross slope of untreated surface gravel road must be sufficient enough to drain water to prevent potholes and softening of the roadway; thus: • If Road materials are sufficiently stable and water tight, one inch per slope is considered satisfactory although 3/8 to ½ per slope is preferred • If the road is steep grade, substantial cross slope is needed to direct the water into the roadside Untreated Surface Road- is seldom constructed in less than 20 cm loose depth. When compacted, will be compressed to about 15 cm thick. Road development sometimes adopted the stage construction methods which means, step by step improvement of the roadway, depending upon the availability of funds and demand of increased traffic The sequence of improvement could be as follows: ✓ first: it might be an earth surface ✓ second: untreated gravel road ✓ third: application of asphalt over the gravel ✓ fourth: the use of stone type pavement with gravel as part of the base course F. Sub-grade or Sub-base Coarse Aggregate is classified by DPWH as: The Department of Public Works and Highways classified the aggregate subbase course as Item 200 which consists furnishing, placing, and compacting aggregate sub base course in a prepared sub-grade 1. Item 200- Material Requirements- that, aggregate for sub base shall consist of hard, durable particles of fragments or crushed stone, crushed slag or crushed or natural gravel and filler or natural crushed sand or other firmly divided mineral matter 2. Item 201 Material Requirements Conditions: ✓ That the fraction passing the 0.075 mm (No. 200) sieve shall have a mass percent of wear or to exceed 50. ✓ The fraction passing the 0.425 mm (No.40) sieve shall have a liquid limit not greater than 25 and Plastic Index not greater than 6. ✓ The coarse portion retained on a 2.0 mm (No.40) sieve shall have a mass percent of wear no to exceed 50. ✓ The materials passing the 20 mm (3/4") sieve shall have a soaked CBR value of not less than 80%. C 3. Item 202 Material Requirement ✓ The portion passing the 0.075 mm (No. 200) sieve shall not be greater than 0.66 (2/3) of the portion passing the 0.425 mm (No. 40) sieve. ✓ The portion passing the 0.425 mm (No.40) sieve shall have a liquid limit not more than 25 and Plastic Index not more than 6. ✓ The coarse aggregate retained on 2.0 mm (No. 10) sieve shall have a mass percent of wear not more than 45 by L.A abrasion tests, and not less than 50 mass percent shall have at least one fractured face. 4. Item 203 Lime Stabilized Road Mix Base Coarse- This item consists of foundation for a surface coarse composed of soil aggregate, lime and water proportion mixed on site and constructed on a prepared sub grade or sub- base. Lime Stabilization Steps: a. Scarifying after lime addition. b. Water addition. c. Rotary mixer for initial mixing. d. Final mixing and pulverization after mellowing period. Preparation of the Soil Aggregate ✓ Case 1: For new soil aggregate • The existing roadbed is scarified lightly and bladed to a uniform grade according to the plan, then rolled, watered and rolled. • All depressions appearing on the surface are filled, and the weak portion of the roadbed is strengthened with new soil aggregate. • Allow one day for measuring, sampling and testing of the sample for approval of the quality and gradation before spreading the window for application of the hydrated lime ✓ Case 2: For salvage soil aggregate • When materials in the site are to be used for mixing, the surface should be scarified lightly and bladed to a uniform conforming to the cross section of the plan. • The reshaped surface is scarified again to depth required leaving a foundation of undistributed material parallel with the profile and cross section. • The loosened materials are bladed into a window at the side of the roadway. The undistributed materials are then rolled, watered and rolled 5. Item 204 Portland Cement Stabilized Road Mix Base Coarse- This item consist of a foundation for surface composed of soil aggregate, Portland cement and water, proper proportions of road-mixed placed on a prepared sub-grade or sub-base 6. Item 205 Asphalt Stabilized Road Mixed Base Coarse • Materials. Asphalt materials should be Anionic or Cationic Emulsion asphalt of the slow setting type. • Mixture and Proportion. The amount of asphalt material to be added to the aggregate should be from 4 to 7 mass percent of the dry aggregate 7. Item 206 – Portland Cement Treated Plant Mix Base Coarse a.) Travel Plant Mixing Method – new aggregate is pulverized at least 80 mass percent other than stone or gravel. b.) Central Plant Mixing Method – the plant is equipped with feeding and metering devices that will introduce the cement aggregate and water into the mixer in quantities specified. c.) Spreading, Compacting and Finishing – not more than 60 minutes should elapse from the start of mixing to compaction of the laid mixture. After spreading, the mixture is compacted and finished in accordance with the procedures as enumerated for lime stabilized road mix base course item 2-3. G. Clearing and Grubbing Clearing and grubbing is categorized under Item-100 of the DPWH standard specification. It consists of clearing, grubbing, removing, and disposing of all vegetables matter and debris except the objects that are designated to remain in place or are to be removed in consonance with other provision of the specifications. It also includes preservation from injury or defacement of all objects designated to remain. a. Specification for clearing and grubbing provides that: All surface objects and all trees, stumps, roots, and other protruding obstructions, not designated to remain should be cleared and/or grubbed including the moving required as follows: • • • • • Removal of undistributed stumps and roots and non-perishable solid objects with a minimum depth of 90 centimeters below sub-grade or slope of embankments will not be required. Outside the grading limits of cut and embankment areas, stumps, and nonperishable solid objects should be cut off not more than 15 cm above the ground line or below low water level. In areas to be rounded at the top of cut slope, stumps should be cut off flush with or below the surface of the final slope line. Grubbing of pits, channel changes, and ditches will be required only to the depth necessary by the proposed excavation with such areas. Burning should be under the surrounding vegetation, adjacent property, or anything designated to remain on the right of way will not be jeopardized. b. Methods of Measurement: • • • Area Basis- by hectare and fractions therefore acceptably cleared and grubbed Lump Sum Basis- No measurement of areas will be made for this item. Individual Unit Basis (Selective Clearing)- ex. The diameter of trees will be measured at a height of 1.4 meters above the ground. Trees less than 15 cm diameter will not be measured for payment. Excavation -is the process of loosening and removing earth or rock from its original position in a cut and transporting it to a fill or to waste deposit. c. Classifications of Roadway Excavation: • • • • • Unclassified Excavation- is the excavation and disposal of all materials regardless of its nature, or not classified and included in the Bill of Quantities under other pay items. Rock Excavation- consists of igneous, sedimentary, and metamorphic rocks that cannot be excavated without blasting or the use of rippers and all boulders or other detached stones each having a volume of 1 cubic meter. Common Excavations- are those that are not included in the Bill of Quantities under rock excavation or other pay items. Muck Excavation- consists of the removal and disposal of deposits of saturated or unsaturated mixture of soils and organic matter not suitable for foundation materials regardless of moisture contents. Barrow excavation- is the excavation and utilization of approved materials for the construction of embankments or for other portion of the work obtained from approved sources in accordance with certain requirements The Use of Excavated Materials: All suitable materials removed from the excavation area are used in the formation of: ■Embankment ■Slope ■Sub-grade ■Bedding ■Shoulders ■Backfill for structures All unsuitable materials that could not be properly compacted in embarkment must be disposed of without delay for it might be included in the work when the engineer turns his back for a cup of coffee. Barrow materials should not be placed after the fill accessible roadway excavation has been placed in the fill. III. Learning Activities/Exercises/Essay Questions/ Assessment Questions Test I. Test Your Knowledge Identify what is being described in each number. Write your answer on the blank before the item. ________1. It is a structure onto which the road base course is laid. ________2. The world's oldest known paved road was laid in this country sometime between 2600 and 2200 BC. ________3. The part of roadway where the sub-base consists of transported materials taken from nearby roadway cuts or from borrow pit. ________4. It consists of large pebbles or crushed rock particles combined with either clay, lime, iron oxide or other fine materials sufficient enough to serve as binder of the coarse particle. ________5. It is seldom constructed in less than 20 cm loose depth. ________6. It is composed of either loose beach sand, dune pit or river sand cemented with asphalt materials. _______7. It is the process of loosening and removing earth or rock from its original position in a cut and transporting it to a fill or to waste deposit. ________8. It is the excavation and disposal of all materials regardless of its nature, or not classified and included in the Bill of Quantities under other pay items. ________9. These are those that are not included in the Bill of Quantities under rock excavation or other pay items. ________10. This item consists of foundation for a surface coarse composed of soil aggregate, lime and water proportion mixed on site and constructed on a prepared sub grade or subbase. Test II. Expand Your Knowledge Answer the following questions briefly. Make sure to provide a brief explanation for each of your answer. 1. What are some of the most important things that you need to know before constructing a roadbed? 2. Is roadbed construction done the same way across all areas regardless of an area’s geography? 3. Do you think excavated materials can no longer be used? If no, what could be their uses? Test III. Apply Your Knowledge Explain what is shown in the pictures below. Write your explanation in 4 to 5 sentences. 4. 5. Answer Key for Test 1 1. Roadbed 2. Egypt 3. Fill Section of Road 4. Gravel Road 5. Untreated Surface Road 6. Sand and Asphalt Base Coarse 7. Excavation 8. Unclassified Excavation 9. Common Excavations 10. Item 203 Lime Stabilized Road Mix Base Coarse IV. Reference/s JICA 報告書 PDF 版(JICA Report PDF). (n.d.). https://openjicareport.jica.go.jp/ Mitrovic, P. (n.d.-a). THE PRINCIPLES OF THE TECHNOLOGY OF CONSTRUCTION OF ROADBED. https://trid.trb.org/view/491847 Road Bed Construction. (n.d.). Scribd. https://www.scribd.com/presentation/426331736/Road-Bed-Construction Types of excavation. (n.d.). Designing Buildings.https://www.designingbuildings.co.uk/wiki/Types_of_excavation Typical Road Structure Cross Section - Sub Grade, Base Course, Sub Base, Wearing Course. (n.d.). https://www.aboutcivil.org/road-structure-cross-section.html Varga, T. (2023, April 12). One of the Oldest Known Engineered Roadways Is a 5,830-YearOld Timber Causeway That Has Been Remarkably. Earthly Mission. https://earthlymission.com/sweet-track-causeway-somerset-levels-oldest-knownengineered-roadways-5830-year-old-timber-wood-well-preserved 张胜. (2009, April 3). CN101545234A - Method for constructing roadbed and base course by construction waste - Google Patents.https://patents.google.com/patent/CN101545234A/en Links: https://docs.nzfoa.org.nz/live/nz-forest-road-engineering-manual-operatorsguide/earthworks/cut-and-bench-fill-construction/ https://www.scribd.com/presentation/426331736/Road-Bed-Construction
