Embankment Construction Method Statement Including Soil Stabilization & Granular Sub Base

Below is a precise roadwork method statement that covers construction of embankment including soil stabilization and sub base preparation, with material obtained from approved borrow areas or suitable material obtained from roadway excavation and drain excavation etc.

The embankment construction work shall be preformed in compliance with, contract agreement, Ministry of Road Transport & Highway Specifications, Relevant Drawings and applicable local and international codes and standards.

Below is list of necessary tools and equipment for performing the road works.

• • Excavator
  • Tipper Truck
  • Motor Grader
  • Vibro Roller (Soil Compacter)
  • Water Tanker
  • Tractor
  • Rotovator

Embankment Construction Method

Working area for construction of Embankment and Subgrade is to be fixed according to drawing.

Boundary / toe line points shall be marked with lime.

Approved earth from borrow area or Excavated area shall be brought to site with the help of tipper.

Soil clouds larger than 75 mm size shall be broken manually before spreading.

Earth will be spread over the working area with the help of grader or loader to the desired loose thickness.

Layer thickness shall be constructed 250 mm to 300 mm in loose state and compacted to 200 to 250 mm thickness as per drawing.

To control the loose / compacted layers thickness pegs will be fixed at each 20 meter interval.

Required level will be marked on each peg for thickness control.

Natural Moisture of the Borrow material shall be checked at site with the help of Moisture Meter for each 500 square meter area.

Moisture shall be maintained near OMC by sprinkling water throughout the soil uniformly with the help of Control Water bowser.

The earth will be spread and graded by Grader for uniformity, then compacted with the help of vibratory roller of 8-10 tons static weight at least 5 to 6 passes consisting of Plain, Light, Medium or High vibration.

Density shall be checked and maintained to 95% for Embankment / subgrade and pick the levels also.

If compaction is found less than 95% for embankment / subgrade, the layer should be re-compacted with vibratory roller by sprinkling water if necessary.

The density of layer shall be rechecked with respect to laboratory Maximum Dry Density with help of Sand Replacement Method.

If the density of layer is not achieved, the layer shall be harrowed with the help of grader. Then layer natural moisture content shall be checked with the help of Laboratory calibrated Rapid Moisture Meter. If the Moisture is not close to OMC, additional water shall be spread uniformly throughout and uniformly mixed by Mechanical means using Disc Harrow / Grader.

If the moisture content is found more than OMC, then the bed shall be kept for drying for few hours until the earth attains moisture nearer to OMC.

The contractor will inform client about next days’ work program for taking field density and level checking.

After achieving specified density next layer filling will proceed.

Test Frequency and surface finish shall conform to the requirements of approved inspection and test plan / ITP.

Soil Stabilization Method

Subgrade material shall be spread on the top of embankment layer (200mm + 25% loose) and levelled with the help of a motor grader to uniform thickness.

Total work area shall be marked with grids of the area required for one bag of cement (approx. 2.5m X 2.5m).

Cement shall be spread at the rate of one bag per grid. Actual rate of spread of cement shall be as per the approved mix design.

Soil and Cement shall be mixed by mechanical Harrow followed by tractor mounted rotavator.

Moisture shall be added to the soil to bring it to OMC of the soil-cement mix (+1/-2% of OMC).

Compaction shall be carried-out with the help of earth compactor to bring the layer to min 98% compaction level with respect to mix maximum dry density as per applicable standards.

Quality Control tests (compaction level, layer thickness and surface level & regularity etc.) shall be conducted as per the approved ITP immediately after layer compaction is completed.

After the layer is checked and found OK in above tests, it shall be left for 7 days for curing by covering it with wet hessian cloth.

The soil-cement mix samples shall be collected from the site and CBR specimens prepared in the laboratory for the compressive strength testing.

Soaked CBR tests shall be conducted on the specimens at 7 days’ age to check conformance with the criteria established during mix design.

Once the cured cement soil mix is found to meet the CBR criteria, it shall be approved by the consultant/client and construction of next layer shall be started.

Granular Subbase Method

This work shall consist of laying and compacting of well-graded materials on a prepared and approved sub-grade.

Materials shall be laid on one or more layers as per line and level, grade and cross section shown in the drawing or as directed by the consulting engineer.

The material used in GSB shall be mixture of natural sand, Crushed gravel, crushed stone & Crushed Slag shall satisfy Grading given in specification.

Required testing will be done and test report will be forwarded to the Engineer after the tested material satisfies the specification requirements.

The material for GSB shall be obtained from the approved source only.

Prior to laying of GSB, approved sub-grade is rolled with two passes by 80 – 100 KN smooth wheeled roller with slight sprinkle of water.

A trial run will be prepared with the mix on the prepared Sub-grade to decide the loose spread thickness and water content so as to achieve the required compacted thickness of one layer.

Size of trial bay for GSB shall be 10m x 75m.

The Granular Sub-base (herein after called GSB) Material is spread with the help of motor grader/JCB/Loader on the approved layer of Sub-grade.

During spreading and mixing by grader in site, water is sprinkled over the material by water bowser mounted on water tanker.

Sufficient water is added taking into account of evaporation losses so that moisture content of the materials should lie in between +1% & -2% of optimum moisture content. Immediately rolling starts with vibratory roller of 80 to 100 kN static weight with plain drum.

Rolling is done from lower edge towards upper edge longitudinally for the portion having unidirectional cross fall and super elevation.

For the portion having cross fall in both sides, rolling should commence from outer edge towards crown (center) of the carriageway.

Each pass of the roller shall uniformly overlap not less than one third of the track made in the previous pass.

During rolling, grade and cross fall shall be checked and any high spot or depressions, which become apparent, shall be corrected by adding or removing fresh materials.

The speed of roller shall not exceed 5km/h.

Rolling shall be continued till the density of the layer is achieved 98% of the Maximum Dry Density.

After achieving at least 98% MDD than pick the levels of GSB top layer.

HSE Requirements for Embankment Work

For locations where the dumping of embankment materials by tippers are performed, a minimum of 2 flagmen with reflective vests and holding a red flag each shall be deployed to control the vehicle which may be affected by the unloading operation.

All locations where embankment construction is in progress, shall be provided with visible safety signs.

The Safety officer shall make frequent patrols along the roadway to ensure that the safety equipment and signs are operational at all time.

Vehicles tracks shall be kept moist to prevent flying of dust particles with the vehicle movement.

Stock pile shall be sprinkled lightly with water prior to its mixing & transportation to site to control the air pollution.

Provisions given in the Contract Agreement, specifications, drawings, approved mix designs & ITP shall get precedence over this roadwork method statement.