IRC 36:2010 is the Indian Standard (IRC) for recommended practice for the construction of earth embankments for road works. This IRC code outlines best practices for constructing stable and durable earth embankments, crucial for road infrastructure. It emphasizes material selection based on soil properties, particularly plasticity and shear strength, and details rigorous compaction requirements to achieve specified densities and prevent future settlement. The code also addresses construction techniques such as layer thickness, moisture content control, and placement methods, along with essential quality control measures like field density tests and moisture content checks. Adherence to these guidelines is vital for ensuring the long-term performance and safety of road networks.
This IRC code provides recommended practices for the construction of earth embankments for road works. It covers materials, compaction, construction methods, and quality control to ensure the stability and durability of embankments.
Key material properties, compaction standards, density requirements, and construction tolerances for building stable and durable road embankments.
| Reference | Value | Clause |
|---|---|---|
| Min Compaction (Subgrade)— For top 500 mm of embankment and earthen shoulders. | 97% of MDD | Cl. 7.3 |
| Min Compaction (Embankment)— For general earth fill. | 95% of MDD | Cl. 7.3 |
| Max Compacted Lift Thickness— For soil/granular material. | 250 mm | Cl. 7.2.2 |
| Compaction Moisture Content— For normal soils. Varies for expansive clays. | OMC ± 2% | Cl. 7.2.3 |
| Min Soaked CBR for Subgrade— For new National/State Highways. | 8% | Cl. 3.2.2.3 |
| Max Particle Size (Subgrade)— For top 500 mm of embankment. | 50 mm | Cl. 3.2.2.1 |
| Max Particle Size (Embankment)— For general embankment fill. | 75 mm | Cl. 3.2.2.1 |
| Unsuitable Soil: Max Liquid Limit— Soils with LL > 70 are generally considered unsuitable for fill. | 70 | Cl. 3.2.2.2 |
| Unsuitable Soil: Max Plasticity Index— Soils with PI > 45 are generally considered unsuitable for fill. | 45 | Cl. 3.2.2.2 |
| Max Organic Content— For embankment and subgrade fill material. | 2% | Cl. 3.2.2.2 |
| Max Soluble Sulphate Content | 0.5% | Cl. 3.2.2.2 |
| Min CBR for Top 500mm Fill— Material with CBR < 3 should not be placed in the subgrade portion. | 3% | Cl. 3.2.2.3 |
| Compaction for Expansive Clays— Compacted at moisture content of OMC to OMC+2%. | 90-95% of MDD | Cl. 7.3 |
| Max Lift Thickness (Rockfill)— May be increased with specific approval and vibratory rollers. | 500 mm | Cl. 8.3 |
| Surface Level Tolerance— Value from MoRTH Spec Table 900-1, referenced by this clause. | ± 20 mm | Cl. 9.3 |
| Formation Width Tolerance— Value from MoRTH Spec Table 900-1, referenced by this clause. | +50 mm / -25 mm | Cl. 9.3 |
| Crossfall Tolerance— Value from MoRTH Spec Table 900-1, referenced by this clause. | ± 0.5% | Cl. 9.3 |
| Field Density Test Frequency— Value from MoRTH Spec Table 900-2, referenced by this clause. | 1 test per 1000 m² | Cl. 9.2 |
| MDD/OMC Test Frequency— For each type of borrow material. Ref: MoRTH Table 900-2. | 1 test per 3000 m³ | Cl. 9.2 |
| Material Property Test Frequency— For borrow material (LL, PI, Gradation). Ref: MoRTH Table 900-2. | 1 test per 3000 m³ | Cl. 9.2 |
IRC 36 specifies the recommended practice for the construction of earth embankments for road works — the standard for forming the road embankment from selected fill material, including subgrade preparation, layer thickness, compaction, drainage, and acceptance.
Use IRC 36 for any: - New highway embankment construction (NH, SH, MDR, ODR, village road) - Widening of existing roads requiring new fill - Approach embankments to bridges and overpasses - Reinforced soil walls (along with IRC SP 102 / SP 82) - Service road construction - Industrial / port / airport earthworks where road surfaces will follow
IRC 36 covers conventional earth embankments. For specific challenging conditions, supplementary codes apply: - Black cotton (expansive) soil — IRC:91 / IRC SP 100 - Lateritic soil — IRC:91 - Marine silty clays — site-specific design + ground improvement - Reinforced soil walls (slopes > 30°) — IRC SP 82:2015 - Rock cuttings (the cut counterpart to embankment fill) — IRC:74
IRC 36 is referenced by: - MoRTH Specifications for Road and Bridge Works (Section 300 — earthwork) - NHAI standard contracts - PMGSY (rural roads) — adapted for low-volume embankments via IRC SP 72:2015 - State PWD specifications across India
Sources of fill (in descending preference): 1. Borrow areas adjacent to road alignment — best logistics 2. Cut sections of the same project — balanced earthwork 3. Approved external borrow sites 4. Approved manufactured fill (granular base, stabilised soil, recycled material)
Acceptable soil types (Clause 5): - Sandy soils, gravelly soils - Silty soils with PI ≤ 12 - Clayey soils with PI < 25 and LL < 50 — provided compaction control is strict - Black cotton soil and other expansive soils — only with additional treatment (lime stabilisation, capping with non-expansive granular layer)
Unacceptable materials: - Organic soils (peat, topsoil, marsh deposits) — biodegradable, settle over time - Soluble salts (chlorides, sulphates) — corrosive to drainage pipes and culverts - Pyritic soils — oxidise to sulphuric acid in service - Rubbish, building waste, industrial slag (without specific approval)
Selected material for upper subgrade (top 500 mm): - CBR ≥ 8 % (in soaked condition, at 98 % MDD per IS 2720 Part 17) - Liquid Limit ≤ 50, Plasticity Index ≤ 25 - Free of organic matter, soluble salts - Maximum particle size: 75 mm (top 500 mm); 90 mm (lower body)
Selected material for embankment body (below top 500 mm): - CBR ≥ 4 % (less critical than upper subgrade) - Otherwise as above
Compaction requirements (Clause 7, the headline numbers):
| Layer position | Compaction (% Standard Proctor MDD per IS 2720 Part 7/8) | |---|---| | Top 500 mm subgrade | 98 % MDD | | Embankment body (below 500 mm) | 95 % MDD | | Earthen shoulder | 95 % MDD | | Sub-grade beneath culverts/structures | 98 % MDD |
Layer thickness during construction: - Loose lift: 200-300 mm (compacted to 150-225 mm) - Maximum compacted lift thickness: 250 mm - Each lift fully compacted before next is placed
Moisture content control: - Compact at OMC ± 2 % (per IS 2720 Part 7) - Below OMC: insufficient compaction, dry density not reached - Above OMC: shear failure during rolling, mud pumping - For black cotton / expansive soils: compact dry of OMC by 2-4 % (avoids swell on subsequent wetting)
Side slope (Clause 8): - Embankments up to 6 m height: 1V : 2H - Embankments 6-9 m: 1V : 2.5H - Embankments > 9 m: site-specific stability analysis required - Special soils: flatter slopes (e.g., 1V : 3H for black cotton)
Setback from edge (for safety): - Top of embankment: kerb / parapet / barrier per IRC:5:2015, IRC:99 crash barriers - Toe of embankment: side drain at 1-2 m offset
Acceptance testing frequency: - Density test: 1 per 1000 m² per layer (random) - Gradation test: per source change, per 5000 m³ thereafter - CBR: per source qualification + per 10,000 m³ - Atterberg limits: as for gradation
1. Compacting at wrong moisture content. Below OMC: density falls short of MDD; rolling adds little. Above OMC: rubber-tyre roller pump, 'bulging' shows under roller. Daily moisture check by speedy moisture meter or oven on a sample. 2. Layer too thick. Loose lift > 300 mm cannot be compacted to 95-98 % MDD by standard rollers. Reduce to 150-200 mm compacted thickness; verify by dry-density-cone or sand-replacement test. 3. Black cotton soil in embankment without treatment. BC soil swells/shrinks dramatically with moisture; embankment heaves, road cracks. Either: cap with 500 mm non-expansive granular layer, OR stabilise with 5-7 % lime, OR replace top 500 mm with selected granular fill. 4. No drainage during construction. Rainwater pools on partial embankment, soaks lower layers; rolling becomes ineffective; staged construction loses days. Provide perimeter ditches, slope toward drains. 5. Borrow material accepted without testing. Visual identification is insufficient. Demand grading, Atterberg limits, CBR, and oversize content test for every borrow source. 6. Side slope too steep. 1V:1.5H or steeper in cohesive soils risks shallow slope failures during monsoon. Stick to 1V:2H minimum for any embankment > 3 m. 7. Subgrade prepared on top of disturbed/loose soil without re-compaction. The original ground surface should be stripped of topsoil, ploughed and re-compacted to 95 % MDD before embankment fill begins. 8. Embankment over weak foundation soil without ground improvement. If foundation soil is c_u < 25 kPa OR CBR < 2 %, embankment may fail by base shear or settle excessively. Apply ground improvement (PVD with surcharge, vibrocompaction, geogrid reinforcement) per IRC:34 or specific design. 9. Heavy rolling on freshly-placed subgrade in rainy season. Rolls grass-cuttings, mud, water into the subgrade; result is uneven density. Either delay until dry, or use vibration only with a tamping roller. 10. No 'proof rolling' before placing pavement layers. The standard pre-pavement check is a heavily-loaded roller pass — any spongy spots indicate insufficient compaction below; replace before pavement layers are placed.
Standard road construction cascade for a typical project:
1. Survey + design — alignment, profile, cross-section, soil testing. 2. Right-of-way clearance — land acquisition, tree felling, utility shifting. 3. Site preparation — strip topsoil (200-300 mm typical), grub out vegetation, original-ground proof rolling. 4. Drainage works first — culverts, cross-drainage, side drains positioned ahead of embankment construction. 5. Embankment construction (this code, IRC 36): - Source selected fill from approved borrow / cut - Lay loose lifts 200-250 mm - Bring to OMC ± 2 % (water-add or aerate-dry) - Compact to 95 % MDD (body) / 98 % MDD (top 500 mm subgrade) - Test density per 1000 m² per layer; reject and re-compact if below threshold - Repeat lifts up to design profile 6. Subgrade finishing — top 500 mm to 98 % MDD with selected material (CBR ≥ 8 %). 7. Pavement construction (IRC:37 for high-volume / IRC SP 72 for rural): - Granular sub-base (GSB) - Wet-mix macadam (WMM) base course - Bituminous courses (DBM + BC) or surface treatment 8. Shoulders + side drains (as per cross-section). 9. Road furniture — kerbs, road signs, line markings, crash barriers. 10. Defect-liability period — typically 1-2 years for highways, 3-5 for PMGSY rural roads.
The embankment is the foundation of the entire pavement above. Any compromise on IRC 36 quality cascades into early pavement failure — under-compacted embankment causes settlement, cracking, drain damage. The price difference between strict and lax compaction is small; the long-term cost difference is enormous.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Compaction Energy (kJ/m³) | |||
| Minimum Dry Density (% of MDD) | |||
| Maximum Plasticity Index (PI) | |||
| Optimum Moisture Content (OMC) Tolerance | |||
| Layer Thickness (Compacted, meters) |