2. Clearing and Grubbing
4. Granular Sub Base Course
5. Wet Mix Macadam
6. Prime Coat
7. Tack Coat
8. Bituminous Macadam
9. Dense Bituminous Macadam
10. Bituminous Concrete (Wearing Course)
This document outlines the procedure for the method of construction of major items of Road works true to the lines, grades, shapes and cross sections as per approved drawings and specifications of the Project.
The Standard Specifications for Road and Bridge Works of Ministry of Shipping, Road Transport & Highway (MoSRTH) shall be consulted for the details which are not covered in this document.
1.2 FIELD OF APPLICATION
1. Clearing and Grubbing
3. Granular Sub Base Course
4. Wet Mix Macadam
5. Prime Coat
6. Tack Coat
7. Bituminous Macadam
8. Dense Bituminous Macadam
9. Bituminous Concrete (Wearing Course)
1. Concessionaire Agreement
2. MoSRTH Specifications for Road and Bridge Works
2. CLEARING AND GRUBBING
To out line the procedure for method of construction of Clearing and Grubbing to the required dimensions and levels conforming to approved drawings and project specifications.
2.2 CONSTRUCTION EQUIPMENT:
• Bull Dozer
• Motor Grader
• Soil Compactor
• Wheel Loader
• Water Tanker
• Dump Trucks
2.3 CONSTRUCTION METHODOLOGY:
The following sequence of activities shall be carried out for Clearing and Grubbing work:
a The original ground level at every 20m interval longitudinally and 3m transversely and also at CL, edge of shoulder and toe of the existing road shall be recorded. In widely varying terrain and in sharp curve portions the longitudinal spacing may be reduced to 10m.
b The toe width with respect to finish road level shall be calculated & marked it on the ground with an additional margin on both sides of carriageway.
c The centerline of proposed road shall be marked from the given reference point on ground with pegs.
d Grubbing, uprooting of vegetation, grass, bushes, shrubs, top organic soil not exceeding 150mm in thickness (201.1), rubbish, etc. shall be cleared and removed with the help of dozer, grader & excavator.
e All trees, stumps, etc., falling within excavation and fill lines shall be cut to such depth below ground level that in no case these fall within 500 mm of Subgrade. All branches of trees extending above proposed roadway shall be trimmed.
f All excavations below the general ground level arising out of the removal of trees, stumps, etc., shall be filled with suitable material and compacted thoroughly so as to make the surface at these points conform to the surrounding area.
g Minor undulations and pits shall be cut and filled to obtain clean & clear bed matching to the road profile.
h The moisture content of each layer of soil at the time of compaction shall be from +1% to –2% of optimum moisture content. (305.3.5.2)
i Watering and rolling shall be carried out for bed / foundation layer with vibratory roller having 80 - 100 KN static weight (305.3.6) to achieve 95% relative compaction with respect to laboratory dry density found as per Modified Proctor Method (Table:300-2). In case of pits or uneven ground surface where compaction can not be done with vibratory roller, mini tandem rollers or tamping compactors shall be used.
j The compaction control of bed shall be exercised as per Sub section 903.2.2 of MoSRTH Specifications.
k After compaction of the bed, the levels at an interval as mentioned at para (a) above shall be taken before placing of embankment/Subgrade layer.
l All materials arising from clearing & grubbing operations shall be disposed of by the Concessionaire as per Concession Agreement or as directed by the Engineer.
3. EARTH WORKS
To out line the procedure for method of construction of Embankments, Subgrades, Earthen Shoulders and Miscellaneous Backfills to the required lines, grades and cross sections conforming to approved drawings and project specifications.
3.2 CONSTRUCTION EQUIPMENT:
• Bull Dozer
• Motor Graders
• Soil Compactors
• Wheel Loader
• Water Tankers
• Dump Trucks
The materials used in embankments shall be soil, moorum, gravel, a mixture of these or any other material approved by the engineer. These materials shall be free of logs, stumps, roots, rubbish or any other ingredient likely to deteriorate or affect the stability of the embankment.
The maximum laboratory density of material used for embankments up to 3 m height and not subjected to extensive flooding shall not be less than 15.2 K.N/cu.m; and for embankments exceeding 3 m height or embankments of any height subject to long periods of inundation shall not be less than 16.0 K.N/cu.m; and for subgrade and earthen shoulders / verges / backfilling shall not be less than 17.5 KN/cu.m. It shall be ensured prior to actual execution that the material to be used in the subgrade satisfies the requirements of design CBR of 10.
The size of the coarse material in the mixture of earth shall ordinarily not exceed 75 mm when being placed in embankment and 50 mm when placed in the subgrade.
3.4 SOURCE APPROVAL:
Suitable borrow areas shall be identified and samples taken from borrow areas shall be tested for its suitability in Embankments / Sub-grade construction as per specification requirements.
3.5 CONSTRUCTION METHODOLOGY:
The following sequence of activities shall be carried out for construction of earth works:
a After the site has been cleared the limits of embankment shall be marked by fixing pegs on both sides at regular interval as guides before commencing the earthwork.
b The embankment / subgrade shall be built sufficiently wider than the design dimension so that surplus material may be trimmed, ensuring that the remaining material is to the desired density and in position specified and conforms to specified side slopes.
c If the foundation of the embankment is in an area with stagnant water the same shall be removed by bailing out or pumping and the area of the embankment foundation shall be kept dry. Where embankment / backfilling is to be placed under water, only acceptable granular material or rock shall be used.
d Original ground, where necessary, shall be leveled to facilitate placement of first layer of embankment, scarified, mixed with water and then compacted by rolling so as to achieve minimum dry density as per specification i.e. 95% of Lab MDD and 97% of Lab MDD in case of Sub-grade.
e If the difference between the subgrade top level and ground level, in case, is less than 0.5 m and the ground does not have 97% relative compaction with respect to Lab MDD, the ground shall be loosened up to a level 0.5 m below the subgrade level, watered and compacted in layers to not less than 97% of Lab MDD.
f The embankment / Sub-grade material shall be spread in layers of uniform thickness not exceeding 200 mm compacted thickness over the entire width of embankment by mechanical means, finished by motor grader having hydraulic control to achieve specific slope and grade and compacted to achieve required density. Successive layers shall not be placed until layer under construction has been thoroughly compacted to specified requirement and approved by engineer.
g Where the embankment is to be placed over an existing road surface, the work shall be carried out as per Sub Section 305.4.3 of MoSRTH Specifications.
h When the existing embankment and/or subgrade is to be widened and its slopes are steeper than 1 vertical on 4 horizontal, continuous horizontal benches, each at least 300 mm wide, shall be cut into the old slope for ensuring adequate bond with the fresh embankment/subgrade material to be added. The material obtained from cutting of benches shall be utilized in the widening of the embankment/subgrade.
i When the existing slope against which the fresh material is to be placed is flatter than 1 vertical on 4 horizontal, the slope surface may only be ploughed or scarified instead of resorting to benching.
j Moisture content of the soil shall be measured by moisture meter before taking up compaction of each layer as per IS 2720 (Part-2). If the moisture content is less than the designed OMC plus due allowance for evaporation losses as per IS 2720 (Part-2), water shall be sprinkled from a water tanker fitted with c controllable rate of flow to variable widths of surface uniformly without any flooding. After adding required amount of water, the soil shall be processed by means of graders, harrows, rotary mixture or any other method in practice until the layer is uniformly wet.
k The compaction shall be done with the help of vibratory roller of 80-100 KN static weight with plain or pad foot drum or heavy PTR of adequate capacity capable of achieving required compaction.
l Where the width of the widened portion is insufficient to permit the use of conventional rollers, compaction shall be carried out with the help of small vibratory rollers/plate compactors/power rammers or any other appropriate equipment.
m The measurement of field dry density of each compacted layer my be done either by a nuclear moisture / density meter calibrated to provide test results identical to that obtained in accordance with IS 2720 (Part-28) or by sand replacement method as per IS 2720 (Part-28).
n Subsequent layer shall be placed only after the finished layer has been tested and accepted by the Engineer.
o When the embankment / subgrade reaches top position, finishing operations like the work of shaping and dressing the shoulders/verge/roadbed and side slopes shall be done to conform to the alignment, levels, cross sections and dimensions shown on the drawings subjected to the surface tolerance as per Sub Section 902 of MoSRTH Specifications.
4. GRANULAR SUB-BASE
To out line the procedure for the method of construction of Granular Sub-base on prepared subgrade to the required lines, grades and cross sections conforming to approved drawings and project specifications.
4.2 CONSTRUCTION EQUIPMENT:
• Motor Graders
• Soil Compactors
• Water Tankers
• Dump Trucks
The material to be used for the work shall be natural sand, moorum, gravel, crushed stone or combination there of depending upon the grading requirements. Materials like crushed slag, crushed concrete, brick metal and kankar shall be allowed to use only with the specific approval of the engineer. The material shall be free from organic or other deleterious constituents and conform to Grading-I of Table 400-1 of MoSRTH Specifications.
Table 400-1 Grading-I for Close Graded Granular Sub base Materials
IS sieve Designation Percent by weight passing the IS sieve
75 mm 100
53 mm 80-100
26.5 mm 55-90
9.5 mm 35-65
4.75 mm 25-55
2.36 mm 20-40
425 micron 10-25
75 micron 3-10
• The water absorption value of the coarse aggregate shall be determined as per (IS-2386 Part-3). If this value is grater than 2% then soundness test shall be carried out on the material.
• Minimum CBR value for the GSB material for Grade-I is 30%.
• The material passing through 425 micron sieve of GSB material when tested in accordance with IS 2720 part-5 shall have liquid limit and Plasticity Index not more than 25% and 6% respectively.
4.4 SOURCE APPROVAL:
Suitable borrow areas shall be identified and samples taken from borrow areas shall be tested for its suitability in Granular Sub-base construction as per specification requirements.