Field Moisture Content Effects on Shrink-Swell of Clays

Geotechnical engineers have substantial involvement in classification of sites for residential developments in accordance with AS2870-1996 “Resi dential Slabs and Footings” to aid in footing design.

The standard procedure for site classification is based on soil strata and properties. In Australia, the most commonly adopted model incorporates the AS1289 7.1.1-1998 Shrink -Swell Index test method, which is taken to represent the surface movement per unit depth per unit suction change.

The result of the Shrink-Swell test is assumed to be the same if the soil is sampled at different moisture contents. However, the validity of the results when sampled at substantially dry or wet insitu moisture content is uncertain, particularly for highly reactive clays.

This paper discusses an experimental study to measure Shrink-Swell Index of two heavy clays of varying moisture contents. An experimental model was developed to achieve uniform moisture contents within the samples. The results were compared with those from undisturbed samples of the same clay. Statistically significant results were obtained.