Code of practice for design and construction of pile foundations, Part 4: Load test on piles
1985 Edition

IS 2911 Part 4 specifies three principal types of pile load tests:

• Vertical Load Test (Compression): Applies incremental downward loads, generally in 20% steps of the safe load, to ascertain compressive capacity. For raker piles, loading is aligned with the pile axis.
• Lateral Load Test: Evaluates pile resistance to horizontal forces.
• Pull-Out Test: Measures tensile capacity of piles.

Essential information for testing includes pile characteristics, reinforcement details, installation records, soil strata data, water table levels, safe and ultimate load estimates, and details of the reaction system to ensure comprehensive test planning and execution.

Per IS 2911 Part 4 (1985), the safe load determination involves:

• Taking the lower value between two-thirds of the load corresponding to a total displacement of 12 mm (or other specified displacement limits) and the permissible displacement-based load for the structure.
• Applying a suitable factor of safety to the ultimate load capacity derived from the load test.

Load increments are typically about 20% of the safe load, with unloading stages to measure elastic recovery. Tests may proceed up to 50% beyond safe load to observe performance. This approach ensures safety margins while considering displacement behavior.

The standard recommends the following:

• Hydraulic jacks for applying compression or pull-out loads, reacting against rolled steel joists or load frames supported on stable foundations located at least 3 times the pile diameter (or 1.5 m minimum) for compression tests and 2.5 times the diameter for pull-out tests.
• Load measurement via pressure gauges with a sensitivity of 0.01 mm.
• Dial gauges mounted on a datum bar resting on immovable supports at least 3D or 1.5 m from the pile edge to measure settlement.
• Gradual load application with controlled increments and unloading phases lasting at least 15 minutes to capture elastic rebound.

This setup ensures precise load application and displacement measurement for reliable capacity assessment.

Displacement measurement involves:

• Using dial gauges with 0.01 mm sensitivity, positioned in pairs spaced 30 cm vertically on the pile surface.
• For inaccessible cut-off levels, displacement is interpolated using similar triangles; for accessible levels, direct measurement opposite the jack is taken.
• Dial gauge tips rest on a 20-30 mm thick glass plate fixed on a smooth pile surface.
• The datum bar supporting dial gauges is placed on immovable supports at least 3 pile diameters or 1.5 m away.
• Load is applied incrementally with approximately 0.25 mm settlement steps.
• At each increment, load, displacement, and time are recorded in tabular form until settlement rate criteria are met (e.g., 0.1 mm per 30 minutes or 0.2 mm per hour).

This ensures accurate and continuous displacement data for analysis.

Initial pile load tests are conducted primarily for major or critical projects, or when subsurface data is limited, usually involving two or more tests to determine ultimate and safe load capacities, establish acceptance criteria, and assess effects on nearby structures.

Routine tests serve as quality control during production, typically performed on 0.5% to 2% of total piles, to verify safe load capacity and detect anomalies differing from initial test outcomes.

Both test types commonly use the maintained load method, applying incremental loading until displacement rates stabilize within prescribed limits, with tests lasting up to 24 hours or until permissible displacement thresholds are reached.