Code of Practice for Design and
Construction of Pile Foundations
The primary standard governing the design, construction, and testing of pile foundations. Covers driven precast, bored cast-in-situ, driven cast-in-situ, under-reamed, and timber piles — along with load testing procedures.
📋 Multi-Part Standard: IS 2911 is published in four parts with multiple sections. Part 1 covers concrete piles (Sections 1–4), Part 2 covers timber piles, Part 3 covers under-reamed piles, and Part 4 covers load tests. Always use the relevant part for your pile type.
IS 2911 is a four-part series covering the full spectrum of pile foundation types used in practice. Each part addresses a specific pile type or test procedure.
| Part / Section | Title | Pile Type |
|---|---|---|
| Part 1 / Sec 1 | Driven Precast Concrete Piles | Precast RCC / PSC, hammer-driven |
| Part 1 / Sec 2 | Bored Cast-in-Situ Concrete Piles | Bored hole, concrete cast in place (2010) |
| Part 1 / Sec 3 | Driven Cast-in-Situ Concrete Piles | Casing driven, concrete cast in place |
| Part 1 / Sec 4 | Bored Precast Concrete Piles | Under-reamed bored piles |
| Part 2 | Timber Piles | Treated timber, driven |
| Part 3 | Under-Reamed Piles | Bulb-type bored piles in expansive soils |
| Part 4 | Load Tests on Piles | Maintained load, cyclic, lateral tests |
Most Widely Used Section Part 1/Section 2 (Bored Cast-in-Situ) is the most commonly referenced section in building practice, covering the standard mechanically bored pile used in urban construction.
The ultimate load capacity of a single pile is the sum of base resistance (end bearing) and shaft resistance (skin friction). The safe load is obtained by dividing by an appropriate factor of safety.
| Basis of Capacity | Factor of Safety (FOS) | Remarks |
|---|---|---|
| Static load test conducted | 2.5 | Initial test pile; settlement criterion also applies |
| Formula-based only | 3.0 | No load test; higher uncertainty |
| Dynamic formula | 2.5 – 3.0 | Hiley / Engineering News formula; less reliable |
FOS is Not a Substitute for Load Testing IS 2911 strongly recommends conducting initial load tests on at least 0.5% of piles (minimum 2 piles) for every project. Formula-based FOS of 3.0 is a conservative fallback, not a preferred approach.
The most common pile type in urban construction. A hole is bored by mechanical auger or rotary rig, reinforcement cage is lowered, and concrete is cast in place — with or without temporary casing.
| Parameter | Requirement | Clause |
|---|---|---|
| Minimum pile diameter | 300 mm | Cl. 4.1 |
| Minimum reinforcement | 0.4% of gross cross-sectional area | Cl. 7.1 |
| Concrete cover (nominal) | 50 mm | Cl. 7.2 |
| Concrete grade (minimum) | M25 (M30 for marine/aggressive) | Cl. 6.1 |
| Slump for tremie concreting | 150 – 200 mm | Cl. 6.2 |
| Slump for dry boring | 100 – 150 mm | Cl. 6.2 |
| Concreting under water | Tremie pipe method only | Cl. 6.3 |
| Tremie pipe diameter | Minimum 150 mm; max aggregate ≤ 1/4 pipe dia | Cl. 6.3 |
Tremie Concreting Rules The tremie pipe must always be embedded at least 1.5 m into the fresh concrete during pouring. Withdrawing the pipe above the concrete surface causes segregation and voids — a common defect in bored piles.
Pile Cut-off Level Concrete must be cast at least 600 mm above the design cut-off level to allow removal of laitance-contaminated concrete. The top 600 mm is broken away after curing.
When piles are arranged in groups, the group capacity may be less than the sum of individual pile capacities due to group efficiency. Both individual pile failure and block failure of the group must be checked.
| Pile Type | Min. Centre-to-Centre Spacing | Remarks |
|---|---|---|
| Friction piles | 3D | D = pile diameter; reduces overlap of stress zones |
| End-bearing piles | 2.5D | Less critical — load transferred to firm stratum |
| Under-reamed piles | 2× bulb diameter | Measured centre to centre of bulbs |
For block failure, the group is treated as a single large pier with dimensions equal to the pile group plan area. The block capacity is computed as the sum of base resistance of the block and perimeter skin friction. The lesser of block capacity and sum of individual capacities governs.
Pile Cap Design IS 2911 requires the pile cap to be designed to transfer loads from the column to all piles in the group. Minimum pile cap thickness = pile diameter + 150 mm or 300 mm, whichever is greater. Pile cap must extend at least 150 mm beyond the outermost pile edge.
Negative skin friction (NSF) occurs when the surrounding soil settles relative to the pile shaft — typically in soft compressible soils, fills, or areas with surcharge loading. Instead of contributing to pile capacity, the settling soil drags the pile downward, adding to the applied load.
| Mitigation Method | Description | Effectiveness |
|---|---|---|
| Bitumen coating | Coat pile shaft with hot bitumen (2–3 mm thick) | Reduces NSF by 50–80% |
| Slip layer / sleeve | Double-casing or polythene sleeve around shaft | Effective in soft clays |
| Pre-consolidation | Allow fill to consolidate before pile installation | Eliminates future NSF |
| Larger pile diameter | Increases end bearing to offset NSF | Structural approach |
NSF Must Be Included in Design Load IS 2911 requires that negative skin friction be treated as an additional downward load on the pile — not as a reduction in capacity. Ignoring NSF in soft-soil sites is a common design error.
IS 2911 Part 4 specifies procedures for testing piles to verify capacity and performance. Two categories of tests are defined: initial tests (to establish design capacity) and routine tests (to verify workmanship on working piles).
| Test Type | Purpose | Load Level | Number |
|---|---|---|---|
| Initial (Preliminary) Test | Establish ultimate capacity; calibrate design | Up to 2.5× safe load or failure | Min. 0.5% of piles (≥ 2) |
| Routine (Acceptance) Test | Verify working pile quality | 1.5× safe load | 0.5–2% of working piles |
| Cyclic Load Test | Separate base and shaft resistance | Incremental loading/unloading cycles | As specified |
| Lateral Load Test | Lateral capacity and stiffness | Per design requirement | As specified |
| Acceptance Criterion | Limit | Clause |
|---|---|---|
| Settlement at 1.5× safe load | ≤ 12 mm | Cl. 6.2 (Part 4) |
| Net (permanent) settlement at safe load | ≤ 6 mm | Cl. 6.2 (Part 4) |
| Maintained load hold period | 24 hours at each load increment | Cl. 5.1 (Part 4) |
Pile Integrity Test (PIT) IS 2911 also recognises non-destructive testing methods including the Pile Integrity Test (low-strain sonic echo method) and Cross-Hole Sonic Logging (CSL) for bored piles. PIT detects major defects such as necking, cracks, and voids in the pile shaft without excavation.
Under-reamed piles have one or more enlarged bulbs formed by a special under-reaming tool at the base or along the shaft. They are particularly effective in expansive (black cotton) soils where seasonal swelling and shrinkage cause uplift forces on foundations.
| Parameter | Requirement | Remarks |
|---|---|---|
| Bulb diameter (Du) | 2.5 × shaft diameter (D) | Standard single under-ream ratio |
| Min. spacing (multi-bulb) | ≥ 2 × bulb diameter (Du) | Centre to centre of bulbs |
| Min. pile length | 3.5 m below ground level | To anchor below active zone |
| Bulb depth (expansive soils) | Below 1.5 m (active zone depth) | Varies by region; 2 m in some areas |
| Concrete grade | M20 minimum | M25 preferred |
Ideal for Expansive Soils Under-reamed piles are the recommended foundation type for low-rise buildings on black cotton soil (vertisols). The bulb anchors the pile below the active zone, resisting both downward loads and seasonal uplift forces from soil swelling.
Multi-Under-Reamed Piles Where greater capacity is needed, two or more bulbs can be formed along the shaft. The spacing between bulbs must be at least 2Du to prevent interference between the bearing zones of adjacent bulbs.