Expansion Potential According to Uniform Building Code

A common procedure to determine the expansion potential of a soil is to use the Uniform Building Code expansion index test. The soil sample is compacted into a confining ring using a specified compaction energy. If the degree of saturation is between 49% and 51%, the specimen is ready for testing, or else the test specimen procedure is repeated after adjustment of initial water content. The Uniform Building Code expansion index test attempts to control all variables that influence the expansive characteristics of a particular soil. Yet soils having low specific gravity and clayey gravels may not be accurately classified. This is because the test specifications require the use of a specific gravity of 2.7 and there is no correction to account for particles retained on the No. 4 sieve. The expansion index should also be calculated at the end of primary swell, rather than at the time indicated in the test specifications. The weighted expansion index is used for nonuniform soils, but virtually ignores the expansiveness of the soil below a depth of 0.91 m (3 ft).