Embankment Construction Methodology with Quality Control – MoRTH Clause 305
Scope of Work
The work shall consist of construction of embankment with approved and specified materials obtained from approved borrow areas or suitable material obtained from roadway excavation and drain excavation and in accordance with clause 305 of MORTH specifications.
Reference Standards
- MoRTH Specifications – Section 305 (5th Revision)
- IRC SP: 84
- IS 2720 Series – Soil Testing
- Approved Project Drawings
Manpower & ResponsibilitiesManpower & Responsibilities
- Construction Manager
- Engineer / Supervisor
- Land Surveyor
- Material Engineer
- Safety Supervisor
- Helpers
Construction Manager
He shall be overall responsible for the activity including:
- Planning and organizing resources required for execution in consultation with the Project Manager.
- Implementation of safety requirements during the work including utility services protection.
- Ensuring all relevant tests are conducted as per specification.
- Maintaining all QA/QC records as per contract requirements.
- Coordinating with the consultant engineer for obtaining necessary approvals for completed activities.
Engineer / Supervisor
Responsibilities include:
- Deployment of required resources at site as per planning.
- Execution of work as per approved drawings.
- Maintaining quality control as per specifications.
- Implementation of safety regulations at site.
- Obtaining approvals for completed works from consultant/authority.
Land Surveyor
Responsibilities include:
- Establishing reference points for alignment and levels.
- Ensuring correct setting out of works.
- Checking and recording levels of completed work.
- Coordinating with consultant staff for final approval of finished works.
Material Engineer
Responsibilities include:
- Implementation of quality procedures as per approved plan.
- Ensuring all materials meet specification requirements.
- Conducting required laboratory and field tests as per standards.
- Maintaining complete material testing records and reports.
Safety Supervisor
Responsibilities include:
- Ensuring safe execution of all site activities.
- Implementation of project safety plan and guidelines.
- Monitoring compliance of safety measures at site.
Setting Out
After completion of site clearance, the limits of embankment shall be marked by fixing pegs on both sides at regular intervals. The chainage boards and working bench mark shall be set outside the limits of construction areas.
Material Selection & Borrow Area Testing
Selection of Material and Borrow Areas
Material
The material used in embankment shall be soil, moorum, gravel, reclaimed material from pavement, fly ash, pond ash, a mixture of these or any other material approved by the AE. It shall be free of logs, stumps, roots, rubbish and any other material likely to deteriorate or affect the stability of the embankment. The material for embankment shall be obtained from the approved source with preference to the material becoming available from nearby roadway excavation or any other excavation under the contract. The material requirements shall be in accordance with Clause 305.2 of MORTH specifications.
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These materials shall be free from logs, stumps, roots, rubbish or any other ingredients likely to affect the stability of the embankment. The material that has LL less than 55%, PI less than 25%, and Free Swell Index less than 50% shall be used for embankment construction. The material which is having lab MDD 15.2 minimum as per IS: 2720 Part-8 shall be used in embankment filling. The sample from the borrow area shall be brought to the laboratory and tested for the above requirements.
- Clods and hard humps of earth will be broken to a maximum size of 75 mm for embankment.
- If the moisture content (NMC) is less than OMC, the water shall be added by sprinkling considering evaporation losses, so that at the time of compaction it is in the range of 1% above to 2% below the optimum moisture content.
- If NMC is more than OMC, the material can be allowed to dry by exposure to the sun.
EMBANKMENT/STRUCTURE BACK FILLS
The following type of material shall be considered un-suitable.
- Material from swamps, marshes and bogs.
- Peat, log, stump and perishable material.
- Soil classified as OL, OI, OH or Pt. in accordance with IS: 1498.
- Material susceptible to spontaneous combustion.
- Material in frozen condition.
- Clay having LL exceeding 70 and PI exceeding 45 for Embankment.
- Clay having LL exceeding 50 and PI exceeding 25 for Subgrade.
- Material with salts resulting in leaching in the embankment.
- Soils having free swelling index more than 50% shall not be used as filled material.
- Soil having acceptedbelow free swelling index (non-expensive soils) shall be used up to 500 mm below sub-grade/embankment top.
- Fill material having soluble Sulfate content exceeding 1.9 gm. of Sulfate per liter (As per BS: 1377 test 10) not to be deposited with 500 mm in contact with concrete structure or cement bound materials forming part of permanent work.
- Fill material having total Sulfate content exceeding 0.5% by mass. (Tested as per BS: 1377 test 9) shall not be deposited with 500 mm of metallic item forming part of Permanent Work.
- The maximum size of coarse material in earth mixture shall not exceed 75 mm for embankment fill and 50 mm for sub grade fill.
- Soil material shall satisfy density requirement as given in BELOW
Density Requirements for Embankment & Subgrade Material
| Sl. No | Type of Work | Maximum Laboratory dry unit weight when tested as per IS: 2720 (Part 8) |
|---|
| 1 | Embankments up to 3.0 m high not subjected to extensive flooding. | Not less than 15.2 KN/cum or 1.55 gm /cc. |
| 2 | Embankment exceeding 3.0 m ht. or Embankment of any height subject to long period of inundation. | Not less than 16.0 KN/cum 1.631 gm/cc. or 1.6 gm/cc |
| 3 | Sub grade and earthen shoulder / backfill | Not less than 17.5 KN/cum or 1.784 gm/cc |
Note: Materials used shall satisfy design CBR i.e. soaked CBR shall not be less than 12% and 10% as per design locations for Heavy weight fill material. This below is not applicable for light weight fill material.
Compaction Requirement
The Embankment /sub grade material shall be compacted in one or more layer as per contract. The compacted field density shall meet minimum density requirement as given in BELOW
Compaction Requirements for Embankment & Sub grade
| Sl. No | Type of work/material | Relative Compaction % of max. Laboratories dry density as per IS: 2720 (Part 8) |
|---|
| 1 | Sub grade and earthen shoulder | Not less than 97% |
| 2 | Embankment | Not less than 95% |
| 3 | Ground Supporting the Embankment / Subgrade | Not less than 90% |
Borrow Material
The borrow material shall comply with Clause 305.2.2.2 of the MORTH specifications.
Testing Requirements
| Test | IS Code | Frequency |
|---|
| Free Swell Index | IS 2720 (Part 40) | 1/ 3000 m³ |
| Grain Size Analysis | IS 2720 (Part 4) | 2 / 3000 m³ |
| Atterberg Limits | IS 2720 (Part 5) | 2 / 3000 m³ |
| Modified Proctor | IS 2720 (Part 8) | 2 / 3000 m³ |
| CBR | IS 2720 (Part 16) | 1 / 3000 m³ |
Tolerance
All works performed shall conform to the lines grade cross-section and dimensions shown on the drawings. The tolerance for surface level shall be +20mm or -25 mm.
Check List
The Concessionaire shall check the following
- The material is from approved borrow area.
- The materials conform to acceptance criteria as listed above.
- The gradation of material is within approved envelope.
- The MDD and OMC has been evaluated and approved test result available.
- The CBR value is as specified as per approved pavement design.
- Moisture meter (duly calibrated) is available at site to measure pre compaction moisture content.
- All Engineering plants / equipment required for day work should be in working condition.
- Proper setting out has been carried out and additional control points have been marked on ground to control levels etc. TBM verified.
Equipment’s
The following equipment’s shall be used for embankment construction:
- Hydraulic Excavator
- Dozer
- Dumper (Tipper Trucks)
- Motor Grader
- Vibratory Roller
- Water Tanker
- Tractor Trolleys
- Survey kit / instrument
Method of Construction
Method of Operation
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After completion of site clearance, the limits of embankment shall be marked by fixing pegs at regular intervals before commencing the earthwork. Construction toe line will be more than the design toe line to ensure proper compaction on edges.
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Before commencing the earth work the toe limits of embankment shall be marked.
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The original ground shall be levelled to facilitate placement of first layer of embankment, water is sprinkled and then compacted by rolling so as to achieve minimum dry density as specified in the Table 300-1 of MORTH specifications. The original ground shall be leveled, scarified, mixed with water and compacted to achieve 95% of lab MDD.
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Natural ground soil shall be tested for its suitability. If found unsuitable it shall be replaced with the suitable material.
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M.D.D. of natural ground soil shall be determined, and natural ground shall be tested for dry density, if found less than 95% of M.D.D., the original ground shall be scarified mixed with water and compacted with vibratory roller to achieve minimum specified dry density.
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Unsuitable material occurring in embankment foundation shall be removed and replaced by approved materials laid in layers and suitably compacted to the required and specified degree of compaction.
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The materials for the embankment shall be excavated at borrow areas by excavators and hauled to site by dumpers / tractor trolley.
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The embankment material shall then be spread in layers up to 250 mm (when compacted using vibratory roller / compactor) or up to 200 mm (when compacted using 80-100 kN static roller) thicknesses over the entire area with the dozer and finished by a motor grader. The dumped material shall be spread in uniform thickness by means of grader/mechanical means to achieve specified slopes and grades.
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Clods and hard humps of earth will be broken to a maximum size of 75 mm for embankment.
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Where the existing embankment is to be widened, continuous horizontal benches shall be cut out into the old slope to ensure adequate bond.
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Where water is required to be added, the same shall be sprinkled from a water tanker fitted with sprinkler, uniformly on the surface but without flooding and shall be mixed thoroughly in soil by harrowing until uniform moisture content is obtained throughout the depth of the layer.
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If the moisture content (NMC) is less than OMC, the water shall be added by sprinkling considering evaporation losses, so that at the time of compaction it is in the range of 1% above to 2% below the optimum moisture content.
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If NMC is more than OMC, the material can be allowed to dry by exposure to the sun. If the material delivered to the roadbed is too wet, it shall be dried by evaporation and exposure to the sun till the moisture comes down at/near the OMC level.
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The compaction shall be done with the help of vibratory roller or 8 - 10 tonne static roller. The compaction shall also be done with a vibratory roller of 80-150 KN static weight to achieves 95% of MDD.
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Compaction trial shall be carried out on a suitable stretch to determine the number of passes required for particular type of soil, dumped for embankment, to achieve densities specified in the Table 300-2 of MORTH specifications.
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Based on the trial, actual compaction will be carried out with required number of passes of vibratory roller until the specified density is achieved.
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Rolling shall commence from lower edge and proceed towards upper edge. Rolling shall progress parallel to the centreline of the road uniformly overlapping each preceding track by one-third width. Each pass of roller shall overlap 1/3rd of the preceding pass.
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Rolling shall be continued till the specified density is achieved as per Table 300-2 of MORTH specifications.
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In case specified compaction is not achieved, the material in the soft area shall be removed and replaced with approved material.
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Densities shall be tested by sand replacement method.
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Subsequent layers shall be placed only after the finished layer has been tested as per Clause 903.2.2 and accepted.
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The top levels of the embankment shall be constructed with the approved drawing keeping the variation within tolerance limit as per Table 900-1.
Compaction Requirements
| Location | Minimum Density |
|---|
| Embankment Body | ≥ 95% of Modified Proctor MDD |
| Top 500 mm (Subgrade) | ≥ 97% of Modified Proctor MDD |
Field Quality Control Procedures
Density Control
- Sand Replacement Method – IS 2720 (Part 28)
- Frequency:
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One set of ten measurements of density for each 3000 sqm of compacted area for embankment work and 2000 sqm for subgrade work, or closer as required to yield the minimum number of test results for evaluating a day's work on statistical basis.
Moisture Control
| Parameter | Requirement |
|---|
| Moisture Content |
It is in the range of 1% above to 2% below the optimum moisture content. |
Construction Tolerances (MoRTH 305)
| Item | Permissible Tolerance |
|---|
| Finished Level | ± 20 mm |
| Width | +100 mm / −50 mm |
| Side Slopes | ± 0.5% |
| Layer Thickness | ± 25 mm |
Inspection Checklists
Pre-Construction
- Borrow area approved
- MDD & OMC established
- Original ground compacted
During Construction
- Layer thickness controlled
- Moisture within limits
- Rolling pattern followed
- Field density tests recorded
Post-Construction
- Final levels & slopes checked
- Drainage completed
- Engineer approval obtained
Frequently Asked Questions – Embankment Construction (MoRTH 305)
What is the minimum compaction required?
95% MDD for embankment and 97% MDD for subgrade.
What moisture range is acceptable?
OMC ± 2% during compaction.
Which field density test is preferred?
Sand Replacement Method as per IS 2720 Part 28.
How frequently should field density tests be conducted?
Minimum one test per 500 m² per compacted layer.
Why is embankment QC critical?
It prevents settlement, cracking, and premature pavement failure.
