A Procedure for Determining Volumetric Shrinkage of an Unsaturated Soil

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Courtesy of ASTM International

Measurement of unsaturated soil volumes can be used to monitor drying shrinkage and allows calculation of the volumetric air content/moisture content relationship. From this relationship, the onset of significant desaturation can be established as a bound to the validity of conventional soil testing under saturated conditions and of conventional analysis procedures for the particular soil.

Measurement of soil volumes over the full range of drying shrinkage is difficult because the soil is liquid at high-moisture contents, but changes to a deformed, cracked, unsaturated solid when dry. The method of volume measurement should be accurate and consistent, since it is used to calculate small changes in the small volumes of air present in the soil. Ideally, it should not stress the specimen or interfere with drying. Further, the method should be capable of distinguishing any volumes of air in exterior cracks or depressions in the soil surface. Finally, the method should be easily repeatable to enable progressive measurements of soil volume during the drying process. A simple, fast method of soil specimen volume measurement is described, based on measurement of displaced volumes of toluene in a pycnometer-like flask. It is compared with a method of calculating volumes from one-dimensional measurements of specimen length and moisture content during drying.

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