Highway engineering level III Road construction

Road construction

1. HIGHWAY ENGINEERING III CLASS YEAR: V SEM: I CHAPTER ONE Road construction

2. Introduction

3. Earthwork operations and equipment Earthwork operation includes preparation of road bed, roadway and borrow excavation, embankment construction, slope finishing and earthwork protection. In general the earth work operations involves: Excavating/production Loading Hauling Placing Compacting Grading finishing

4. continued Excavation/production: is the process of loosening and removing earth or rock from its original position in a cut and transporting it to a fill section or to a waste deposit. The equipment used in these operations are different in type and capacity ranging from excavators, dozers to scrapers and diggers. Loading: is the process of picking of loosened materials from ground to carrier media to transport from point of the origin to point of desired destination. Machineries involved in this activity will be loaders, dump trucks & excavators.

5. continued Hauling : is transportation of the material from point of origin to point of destination by means of carrier media. Placing : is even distribution of the material hauled at the site where we intended to fill the roadway, detours, backfills or others. Graders, loaders, excavators and other advanced/ primitive equipment will be used

6. continued Compacting : is the process of densification of the soil with application of mass and/or vibration to attain the desired level of strength and densification. Rollers, plate compactors and other hand tools are the main compacting equipment among others. Grading: the road should be even, jerk less, comfortable and looking good. This is done by shaping and creating the design elevation.

7. continued The process of reshaping to have smooth and comfortable surface is known as grading. Most of the time grader is the main equipment among others. Finishing : this is the decorative and aesthetics works of slopes, protection works and other ancillary works related to earthworks.

8. SUBGRADE PREPARATION Sub grade is the natural or existing ground. On reconstruction projects it could include demolishing and disposal of existing facilities. If unsuitable materials such as soft plastic silts or clays are encountered at shallow depths (0.9 to 1.5 m) and extending over large areas, it will be prudent to remove and replace these materials with suitable granular materials. The backfill material should be compacted. If these materials extend to greater depths and area, other means of stabilization should be explored.

9. continued Prior to commencing preparation of the SUBGRADE, Culverts , cross drains , ducts and the lie (including their fully compacted backfill), ditches , drains & drainage outlets shall be completed . Any work on the preparation of the sub-grade shall not be started unless prior work herein described shall have been approved by the Engineer. Subgrade AC Base

10. SUBGRADE LEVEL 0F TOLERANCES: The finished compacted surface of the sub-grade shall conform to the allowable tolerances as specified hereunder: 1 Permitted variation from design LEVEL OF SURFACE + 20mm - 30mm 2 Permitted SURFACE IRREGULARITY measured by 3-m Straight Edge 30mm 3 Permitted variation from design CROSSFALL or CAMBER +/- 0.5% 4 Permitted variation from design LONGITUDINAL GRADE over 25m length +/- 0.1%

11. SUB-GRADE IN COMMON EXCAVATION : If the material is suitable , it shall be set aside for future use. Otherwise dispose if unsuitable. Where material has been removed from below sub-grade level, the resulting surface shall be compacted.

12. SUB-GRADE IN ROCK EXACAVATION Surface irregularities under the sub grade level remaining after trimming of the rock excavation shall be leveled by placing specified material and then compact. SUB-GRADE ON EMBANKMENT After embankment has been compacted, The full width shall be conditioned by removing any soft or unstable material that will not compacted properly the resulting areas such as low sections, holes or depressions shall be brought to grade with suitable materials then the entire roadbed shall be reshaped and compacted to the requirements and shaped to the cross-sections shown on the Plans .

13. SUB-GRADE ON EXISTING PAVEMENT: Where the new pavement is to be constructed immediately over an existing asphalt concrete pavement or gravel surface pavement, and if specified in the Contract, the pavement shall be scarified, thoroughly loosened, reshaped & compacted. The resulting sub-grade level as part of the pavement construction shall be shaped to conform the allowable tolerances by placing & compacting a leveling course to be placed immediately above.

14. SUBBASE COURSE Aggregate Sub-base Course shall consist of: Placing Furnishing, and Compacting an aggregate sub-base course on a prepared sub-grad e in accordance with the Specification and the Lines, Grades and Cross-Sections shown on the Plans. MATERIAL REQUIREMENTS: Aggregate for sub-base shall consist of hard, durable particles or fragments of crushed stone, crushed slag, or crushed or natural gravel and filler of natural or crushed sand or finely divided mineral matter . The composite material shall be free from vegetable matter and lumps or balls of clay and compacted readily to form a firm, stable sub-base.

15. continued The fraction passing 0.425mm (No.40) sieve shall have the following spcs : a) LL ≤ 35 As determined by AASHTO T 89 & T 90 b) PI ≤ 12 The coarse portion, retained on a 2.00mm (No. 10) sieve, shall have a mass % of wear not exceeding 50 by the Los Angeles Abrasion Tests as determine by AASHTO T 96. The Sub-base shall have a soaked CBR value of: Not less than 25% as determined by AASHTO T 193 . Likewise, the CBR value shall be obtained at the maximum dry density and determined by AASHTO T 180, Method D.

16. Construction Requirements: 1 . PREPARATION OF EXISTING SURFACE The existing surface shall be graded & finished as provided under the requirements of SUBGRADE PREPARATION, before placing the Sub-base Material. 2. PLACING Agg . Sub-base material shall be placed at uniform mixture on a prepared sub-grade in a quantity which will provide the required compacted thickness. If more than 1 layer is required, each layer shall be shaped & compacted before succeeding layer is placed.

17. continued when hauling is done over previously placed material, hauling equipment shall be dispersed uniformly over the entire surface of the previously constructed layer. This is to minimize RUTTING or Uneven Compaction . 3. SPREADING AND COMPACTING : When uniformly mixed, the mixture shall be spread to the Plan thickness , for compaction. If thickness is 150mm or less, the material may be spread and compacted in 1 layer. If thickness is more than 150 mm, the aggregate sub-base shall spread and compacted in 2 or more layers of approx. equal thickness

18. continued The moisture content of sub-base material shall, if necessary, Be adjusted prior to compaction by watering with approved sprinkles mounted on trucks or by drying out, in order to obtain the required compaction. Immediately following final spreading and smoothening, each layer shall be compacted to the full width by means of compaction equipment.

19. 4. TOLERANCE Permitted variation from design THICKNESS OF LAYER + - 20mm Permitted variation from design LEVEL OF SURFACE +10mm or -20mm Permitted SURFACE IRREGULARITY measured by 3-m straight-edge 20mm Permitted variation from design CROSSFALL OR CAMBER + - 0.30% Permitted variation from design LONGITUDINAL GRADE over 25m in length +-0.1%

20. 5 . METHOD OF MEASUREMENT : The aggregate sub-base course will be measured by the cubic meter . The quantity to be paid for shall be the design volume compacted in-place as shown in Plans, and accepted in the completed course.

21. BASE COURSE Crushed aggregate base course shall consist of: furnishing, placing and compacting crushed gravel, crushed stone or crushed rock on prepared sub-grade or sub-base in 1 or more layers in accordance with Spacs , lines , grades & thickness. MATERIAL REQUIREMENTS: Crushed Aggregate It shall consist of hard, durable particles or fragments of stone or gravel crushed to the size & of the quality requirements. It shall be clean & free of lumps or balls of clay & other deleterious substances. The material shall be of such nature that it can be compacted readily to form a firm, stable base.

22. continued The portion of the material passing 0.075mm (No. 200) sieve: Shall not be greater than 0.66 (two thirds) of the fraction passing the 0.425mm (No. 40) sieve. The portion of material passing 0.425mm (No. 40) sieve shall have a: 1 . LL ≤ 25 As det. By AASHTO T 89 & T 90 2 . PI ≤ 6 The coarse aggregate retained on a 2.00mm (No. 10 ) sieve shall have a: mass % of wear ≤ 45 by the Los Angeles Abrasion Test

23. continued The material passing the 19mm (3/4”) sieve shall have a: minimum soaked CBR value of 80% tested according to AASHTO T 193. The CBR value shall be obtained the maximum dry density determined according to AASHTO T 180, Method D. If filler is needed, it shall be obtained from sources approved by the engineer, free from hard lumps & not contain more than 15% of material retained on the 4.75 mm (No. 4) sieve.

24. Tolerances Permitted variation from design THICKNESS OF LAYER + - 10mm Permitted variation from design LEVEL OF SURFACE + 5mm or – 10mm Permitted SURFACE IRREGULARITY measured by 3-m straight-edge 5mm Permitted variation from design CROSSFALL OR CAMBER + - 0.2% Permitted variation from design LONGITUDINAL GRADE over 25m in length +-0.1%

25. Surface Course Construction Hot-mix Asphalt Concrete Mix design should be conducted using marshal mix design or super pave mix design methods. In site the asphalt should mix according the proportion of each materials ( i.e aggregate and asphalt content) Include mix segregation, lay down, compaction and joint construction. Segregation is non uniform distribution of various aggregate sizes throughout the mass

26. continued Hot-mix Asphalt Concrete Construction Segregation can occur at the followings stages: mix design, stockpiles; drum mixer operations, discharge systems, truck loading and unloading and paver operations.

27. continued Prime coat is low viscosity asphalt that is applied to a granular base course prior to placement of the asphalt surface course. The purpose of the prime coat is to bond loose material providing a cohesive platform to provide adhesion b/n the base course and surface course to protect the surface of the base course from infiltration of moisture

28. continued Prime coat is generally applied at the rate of 0.1 to 0.3 gal/yd2 or 0.5 to 1.5 l/m2. Tack coat is required to ensure bond between an existing pavement surface and new asphalt overlay. Tack coat should be applied uniformly at a rate of 0.03 to 0.05 gal/yd2 or 0.15 to 0.25 l/m2 for cutback asphalt 0.02 gal/yd2 or 0.1 l/m2 for diluted asphalt emulsion.

29. continued Roller speed should be limited to 3 ml/h or 5 km/h. Many projects are compacted with three rollers: a break down roller, a compaction roller and a finish roller.

30. HMA BATCHING PLANT FOR ADDIS AMBO ROAD PROJECT AT WOLONKOMI

31. Placing ( using paver)

32. Compaction

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