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IS 2911:2021 Part 2 is the Indian Standard (BIS) for design and construction of pile foundations - concrete piles. Code of practice for the design and construction of concrete pile foundations. It details geotechnical bearing capacity calculations, structural detailing requirements, pile spacing, and safe execution methodologies including boring and tremie concreting.
Provides comprehensive design and construction guidelines for various types of concrete piles, including design criteria, load carrying capacity, and reinforcement details.
Quick Reference — Top IS 2911 Part 2:2021 Values
Key design parameters, material specifications, reinforcement details, construction tolerances, and safety factors for concrete piles.
✓ Verified 2026-04-27
Reference
Value
Clause
Min. Concrete Grade (Bored Cast-in-situ)— For piles installed by boring methods.
M25
Cl. 5.2.1
Min. Concrete Grade (Precast)— For precast concrete piles.
M30
Cl. 5.2.1
Min. Cement Content (Moderate Exposure)— For concrete surfaces exposed to normal weather.
320 kg/m³
Cl. 5.2.2.1 (Table 1)
Max. Water-Cement Ratio (Moderate Exposure)— For concrete surfaces exposed to normal weather.
0.50
Cl. 5.2.2.1 (Table 1)
Min. Cement Content (Severe Exposure)— For surfaces exposed to severe rain or alternate wetting/drying.
340 kg/m³
Cl. 5.2.2.1 (Table 1)
Max. Water-Cement Ratio (Severe Exposure)— For surfaces exposed to severe rain or alternate wetting/drying.
0.45
Cl. 5.2.2.1 (Table 1)
Min. Nominal Cover (Moderate Exposure)— Clear cover to main reinforcement.
50 mm
Cl. 5.2.2.2 (Table 2)
Min. Nominal Cover (Severe Exposure)— For coastal environment or severe rain.
60 mm
Cl. 5.2.2.2 (Table 2)
Min. Nominal Cover (Very Severe Exposure)— For surfaces exposed to sea water spray.
75 mm
Cl. 5.2.2.2 (Table 2)
Min. Longitudinal Reinforcement— For piles with length exceeding 6 m.
0.4% of c/s area
Cl. 5.3.1.1
Min. Transverse Reinforcement Dia.— Or 1/4th of main bar diameter, whichever is greater.
8 mm
Cl. 5.3.2.1
Max. Spacing of Links (Mid-height)— Whichever is less.
≤ 0.5 x Pile Dia or 300 mm
Cl. 5.3.2.2
Spacing of Links (At Ends)— For a length of 3 x pile dia from top and 2 x pile dia from bottom.
75 mm
Cl. 5.3.2.2
Min. Pile Spacing (Friction Piles)— For piles deriving capacity mainly from friction.
3 x Pile Dia.
Cl. 6.5.1
Min. Pile Spacing (End Bearing Piles)— For piles resting on rock or hard stratum.
2.5 x Pile Dia.
Cl. 6.5.1
Factor of Safety (Static Formula)— For determining safe load from ultimate capacity via static analysis.
2.5
Cl. 6.10.1.1
Factor of Safety (Initial Load Test)— For determining safe load from an initial load test result.
2.0
Cl. 6.10.1.2
Positional Tolerance in Plan— For single piles or piles in a group of two.
75 mm
Cl. 8.2.1
Verticality Tolerance (Vertical Piles)— Allowable deviation of the pile axis from the vertical.
1.5% (1 in 67)
Cl. 8.2.2
Cut-off Level Tolerance— Permissible deviation of the final pile head elevation.
+25 mm
Cl. 8.2.3
Acceptance: Max Settlement (Routine Test)— At test load of 1.5x working load for a single pile.
12 mm
IS 2911 (Part 4) Cl. 7.1.5.1
Acceptance: Net Settlement (Routine Test)— After removal of test load for a single pile.
≤ 6 mm
IS 2911 (Part 4) Cl. 7.1.5.1
⚠ Verify against the latest BIS/IRC publication and project specifications. Amendment Slips may modify values.
Report on Design and Construction of Drilled Piers
Directly covers 'belled drilled piers,' which are functionally identical to under-reamed piles.
BS 8004:2015+A1:2020BSI (UK)
MediumCurrent
Code of practice for foundations
Covers design and construction of bored piles, including provisions for piles with enlarged bases.
EN 1997-1:2004CEN (Europe)
MediumCurrent
Eurocode 7: Geotechnical design - Part 1: General rules
Provides the design framework for all geotechnical structures including bored piles, but is less prescriptive on specific pile types.
AS 2159-2009Standards Australia (Australia)
MediumCurrent
Piling - Design and installation
Comprehensive standard on piling that includes bored piles with enlarged bases (bells).
Key Differences
≠Prescriptive Geometry: IS 2911 is highly prescriptive regarding the geometry of under-reams, specifying the under-ream to shaft diameter ratio (typically 2.5) and the spacing between bulbs (1.25 to 1.5 times bulb diameter). In contrast, ACI 336.3R provides general guidelines (e.g., bell slope angle) but leaves the final geometry to engineering design based on soil properties and bearing requirements.
≠Application Focus: IS 2911 has a specific and strong emphasis on using under-reamed piles in expansive soils (like black cotton soil) to anchor foundations below the zone of moisture fluctuation. While ACI 336.3R acknowledges the use of belled piers for uplift, its primary focus is on increasing bearing capacity in various soil types, without the same specific emphasis on expansive soils.
≠Multi-Bulb Design: IS 2911 provides explicit design guidance and formulas for multi-under-reamed piles, a common practice in India. Multi-bell drilled piers are significantly less common in US practice, and ACI 336.3R contains limited specific guidance for designing the interaction and capacity contribution of multiple bells on a single pier.
≠Bearing Capacity Formulation for Cohesive Soils: IS 2911 provides a specific formula for the ultimate capacity of piles in cohesive soils (Qu = Ap * Nc * cp + A'p * Nc * c'p + α * c_avg * As), which accounts for bearing at the base and any upper bulbs separately. The ACI approach is more general, applying standard bearing capacity theory to the lowest bell and skin friction to the shaft, with less explicit formulation for the contribution of upper bells.
Key Similarities
≈Fundamental Concept: Both IS 2911 and its international counterparts like ACI 336.3R are based on the same principle: creating an enlarged base (under-ream or bell) on a cast-in-place bored pile to significantly increase its end-bearing capacity and/or uplift resistance.
≈Requirement for Load Testing: Both the Indian Standard and major international codes (ACI, Eurocode) strongly advocate for and provide detailed procedures for conducting pile load tests (static compression, tension/uplift) to verify design assumptions and confirm performance under load.
≈Emphasis on Geotechnical Investigation: All credible pile design standards, including IS 2911 and its international equivalents, mandate a thorough subsurface investigation as a prerequisite for design. The design methodologies in all codes are fundamentally dependent on reliable soil parameters (strength, stratigraphy, density).
≈Construction Principles: The general construction sequence of drilling the shaft, excavating the enlargement (belling/under-reaming), placing the reinforcement cage, and concreting the pile are broadly similar across all standards. They share common concerns regarding borehole stability, cleanliness of the base, and ensuring concrete integrity.
Parameter Comparison
Parameter
IS Value
International
Source
Under-ream / Bell Diameter Ratio (Du/D)
Typically 2.5. Can be up to 3.0 in special cases with permission.
No prescribed ratio; commonly up to 3.0 times shaft diameter, based on design requirements.
ACI 336.3R-14
Vertical Spacing Between Bulbs
1.25 to 1.5 times the under-ream diameter (Du).
Not specified, as multi-bell piers are uncommon. Design would be based on shear analysis between bells.
ACI 336.3R-14
Factor of Safety on Bearing Capacity (from soil properties)
2.5 to 3.0
Generally 3.0 for end bearing and 2.0 to 3.0 for side resistance.
ACI 336.3R-14
Factor of Safety on Bearing Capacity (from load test)
2.5 for initial test; 2.0 for routine test.
Typically 2.0.
ACI 336.3R-14
Minimum Longitudinal Reinforcement
0.4% of pile stem cross-sectional area.
Typically 0.5% to 1.0% of the gross cross-sectional area (references ACI 318).
ACI 336.3R-14 / ACI 318
Bell Slope Angle (from horizontal)
Not explicitly defined; formed by the cutting tool geometry.
Recommended to be at least 45° to 60° for stability, depending on soil type.
ACI 336.3R-14
Concrete Slump (for Tremie/Underwater Placement)
150 - 200 mm
175 - 225 mm (7 - 9 inches)
ACI 336.1-19
⚠ Verify details from original standards before use
Key Values6
Quick Reference Values
minimum longitudinal reinforcement0.4% of gross area
minimum clear cover50 mm
slump for tremie concreting150 mm to 200 mm
minimum spacing friction piles3 times pile diameter
minimum spacing end bearing piles2.5 times pile diameter
minimum grade of concreteM25
Key Formulas
Qu = Ap * Nc * cp + alpha * c * As — Ultimate bearing capacity of pile in cohesive soil
Qu = Ap * (0.5 * D * gamma * Ngamma + pd * Nq) + sum(K * pdi * tan(delta) * Asi) — Ultimate bearing capacity in cohesionless soil