ABSTRACT

The design of foundation systems on expansive soils requires knowledge of unsaturated soil mechanics. Expansive clay minerals are electrochemically active particles, especially in the presence of water. This affinity for water leads to soil mass volume changes with changes in soil moisture content. When a cohesive soil mass hydrates, the materials experience a volume change (termed swelling or heaving), the magnitude of which depends on the clay chemistry and the initial degree of saturation.

The results from the swell test method, which tends to provide a conservatively higher estimate of movement due to the lateral confinement of the soil sample in a steel ring, is used as a basis to design most of the foundation systems. However, this test is not representative of conditions in nature, where the vertical swell strain is only a portion of the total volume change. This test method can also produce conservative estimates of movement due to complete inundation of the sample with water throughout the entire active zone depth, which is not generally typical in-situ. In order to avoid overly conservative design and to provide better performing foundation systems, in this study a heuristic approach is revealed for producing guidelines to design efficient foundation systems at a reasonable cost. The heuristic approach will also be shown to comport with principles of unsaturated soil mechanics.