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Expansion Index

Test Method

ASTM Designation: D 4829, “Standard Test Method for Expansion Index of Soils”

Summary of Test Method

The specimen is compacted into a metal ring so that the degree of saturation is between 40 and 60 % and the specimen and the ring are placed in a consolidometer. A vertical confining pressure of 1 psi is applied to the specimen and then the specimen is inundated with distilled water. The deformation of the specimen is recorded for 24 hours or until the rate of deformation becomes less than 0.005 mm/hour.

The Expansion Index, EI, is used to measure a basic index property of soil and therefore, the EI is comparable to other indices such as the liquid limit, plastic limit, and plasticity index of soils.

The EI is not used to duplicate any particular field conditions such as soil density, water content, loading, in-place soil structure or soil water chemistry. However, the test procedure keeps all conditions constant allowing direct correlation of data between organizations.

The classification of a potentially expansive soil is based on the following table:

Expansion Index, EI Potential Expansion
0–20 Very Low
21-50 Low
51-90 Medium
91-130 High
>130 Very High


Minimum Sample Size

1 Canvas Bag (40 lb)

Last Updated September 29, 2005

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