What is the minimum size of the test plate?

The minimum size is 300 mm (square or circular) with a minimum thickness of 25 mm.

How wide must the test pit be compared to the plate?

The test pit width should be at least 5 times the width of the test plate to minimize confining effects from the pit walls.

When should the plate load test be stopped?

The test is generally continued until a settlement of 25 mm is reached or clear shear failure occurs, whichever is earlier.

What is the frequency of taking settlement readings after applying a load increment?

Readings are typically taken at 1, 2.25, 4, 6.25, 9, 16, 25 minutes, and then at hourly intervals to plot against the square root of time.

IS 1888

: 1982

Method of load test on soils for shallow foundations

CurrentEssentialTesting MethodGeotechnical · Soil and Foundation

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This standard covers the procedure for determining the ultimate bearing capacity, safe bearing pressure, and expected settlement of shallow foundations using an in-situ plate load test. It details the required equipment, test setup, incremental loading procedure, and the interpretation of load-settlement curves for both cohesive and cohesionless soils.

Specifies the method for conducting plate load tests on soils to determine the bearing capacity and settlement characteristics for shallow foundations.

Quick Reference Values

Minimum thickness of bearing plate25 mm

Standard plate sizes300 mm to 750 mm (square or circular)

Minimum width of test pit5 times the width of the bearing plate

Seating load applied before test70 g/cm^2 (approx 7 kPa)

Load increments1/5th of estimated ultimate bearing capacity

Dial gauge sensitivity0.02 mm

Key Formulas

Sf = Sp * [B(Bp + 30) / Bp(B + 30)]^2 — Settlement of foundation in cohesionless soils (dimensions in cm)

Sf = Sp * (B / Bp) — Settlement of foundation in cohesive soils

Practical Notes

The test only stresses the soil to a depth of approximately twice the width of the bearing plate. It may fail to detect deeper weak strata that a full-size foundation would affect.

Water table position significantly reduces bearing capacity. If the water table is expected to rise, tests should be conducted at the simulated water table level or corrected analytically.

In highly cohesive (clayey) soils, total consolidation settlement takes months or years. The standard short-term plate load test provides ultimate bearing capacity but may significantly underestimate total long-term settlement.