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IS 2911:2021 Part 4 is the Indian Standard (BIS) for design and construction of pile foundations - load test on piles. This standard provides the methodology and criteria for conducting initial and routine load tests on pile foundations. It details the setup, procedure, and safe load evaluation criteria for vertical compression, lateral load, and pull-out (uplift) tests to validate foundation design and execution.
Specifies the procedures for conducting various types of load tests on piles to determine their carrying capacity.
Quick Reference — Top IS 2911 Part 4:2021 Values
Key values for pile load testing including test loads, acceptance criteria for vertical, lateral, and pull-out tests, and equipment specifications.
✓ Verified 2026-04-27
Reference
Value
Clause
Initial Test Piles (min)— For projects with >200 piles, min 2 tests are required.
0.5% of total piles, min 1
Cl. 5.1.1
Routine Test Piles (min)— Percentage depends on pile type and strata variability.
0.5% to 2% of total piles
Cl. 5.1.2
Min Concrete Age for Testing— Or when concrete achieves its specified 28-day strength.
28 days
Cl. 5.3
Hydraulic Jack Capacity
≥ 1.25 × Max Test Load
Cl. 6.2.1
Dial Gauge Least Count— For measuring pile movement (settlement/deflection).
0.01 mm
Cl. 6.2.2
Datum Bar Support Distance— D is pile dia. Use the greater value from test pile edge.
≥ 3D or 2.5 m
Cl. 6.2.3
Initial Test - Max Test Load— Or load causing settlement of 10% of pile diameter.
2.5 × Safe Load
Cl. 7.1.1
Initial Test - Load Increment
20% of Safe Load
Cl. 7.1.2
Initial Test - Holding Time (Final Load)— Or until settlement rate is < 0.1 mm/30 min.
24 hours
Cl. 7.1.2
Initial Test - Acceptance (Settlement @ 1.5x Safe Load)— For single piles.
≤ 12 mm
Cl. 7.1.5.1 a)
Initial Test - Acceptance (Net Settlement)— After removing the test load.
≤ 6 mm
Cl. 7.1.5.1 b)
Initial Test - Acceptance (Settlement @ Safe Load)— Alternate criterion from load-settlement curve.
≤ 6 mm
Cl. 7.1.5.2
Routine Test - Max Test Load
1.5 × Safe Load
Cl. 7.2.1
Routine Test - Holding Time (Final Load)— Or until settlement rate is < 0.1 mm/30 min.
12 hours
Cl. 7.2.1
Routine Test - Acceptance (Total Settlement)— At 1.5 times the safe load.
≤ 12 mm
Cl. 7.2.2
Lateral Test - Max Test Load
2 × Safe Lateral Load
Cl. 8.1
Lateral Test - Acceptance (Deflection @ Safe Load)— Or as specified in the design.
≤ 5 mm
Cl. 8.2.1 a)
Lateral Test - Acceptance (Net Deflection)— After removing the test load.
≤ 20% of total deflection
Cl. 8.2.1 b)
Pull-out Test - Max Test Load
2 × Safe Uplift Load
Cl. 9.1
Pull-out Test - Acceptance (Displacement @ Safe Load)— Or as specified in the design.
≤ 5 mm
Cl. 9.2.1 a)
Pull-out Test - Acceptance (Net Displacement)— After removing the test load.
≤ 2 mm
Cl. 9.2.1 b)
⚠ 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