What is the purpose of IS 11550?

To provide a standardized field procedure for measuring the maximum upward pressure exerted by expansive soils when they get wet.

What is the main apparatus required for this test?

A swelling pressure cell (a type of load cell), a reaction frame, and a data recording unit. (Clause 3)

Is this a laboratory test or a field test?

This is a code of practice for field instrumentation, meaning the test is performed on-site (in-situ) within a borehole or test pit.

How long does the test take?

Observations are continued until the swelling pressure reading stabilizes, which can take from several days to several weeks depending on the soil's permeability.

IS 11550

: 1985

Code of practice for field instrumentation of swelling pressure in expansive souls code of practice for field instrumentation of swelling pressure in expansive soils

CurrentSpecializedCode of PracticeGeotechnical · Soil and Foundation Engineering

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This standard specifies the in-situ method for determining the swelling pressure of expansive soils using field instrumentation. It covers the apparatus, installation procedure, and the method for observing and calculating the pressure exerted by the soil upon wetting.

Code of practice for field instrumentation of swelling pressure in expansive souls code of practice for field instrumentation of swelling pressure in expansive soils

Quick Reference Values

Initial seating pressure on cell5 to 10 kPa

Minimum diameter of bearing plate150 mm

Typical observation periodUntil pressure stabilizes (several days to weeks)

Key Formulas

Swelling Pressure (p_s) = P / A; where P is the maximum force recorded by the load cell and A is the area of the bearing plate.

Practical Notes

Ensuring complete saturation of the soil surrounding the instrument is critical for obtaining the maximum swelling pressure, which may require a dedicated water supply system at the test location.

The reaction frame must be sufficiently rigid and anchored well outside the zone of soil influence to provide a stable reference point against the upward soil pressure.

Installation must be done with minimal disturbance to the natural soil structure to get results representative of in-situ conditions.