Measurement and Modeling of the Saturated Hydraulic Conductivity Functions of Collapsible and Expansive Soils

Collapsible and expansive soils cover almost one-fifth of the Earth's land surface. The key feature of these categories of problematic soils is the considerable volumetric strain upon saturation under constant stress. However, most studies on saturated hydraulic conductivity of soils assumed no volumetric tendency of the specimen subjected to water saturation. As a result, a significant error may arise from this assumption in collapsible and expansive soils. In accordance with the standard testing protocols, no modeling approaches regarding the hydraulic conductivity can consider the significant changes in void ratio caused by the saturation-induced collapse or expansion phenomena. Therefore, this study aims to introduce a new modeling framework for the saturated hydraulic conductivity of problematic soils with a marked volumetric tendency upon saturation. Accordingly, 36 tests are conducted on two typical soil types representing collapsible and expansive soils with three levels of saturation-induced volume changes and a wide range of void ratios. All tests are conducted in a low-compliance double-cell twin-burette triaxial permeameter. Afterward, new modeling frameworks based on the Kozeny–Carman model are developed to account for the collapse and swell potentials. The results reveal unique functions between the saturated hydraulic conductivity and the reliable void ratio for both collapsible and expansive soils. Eventually, the performance of new models is validated against some independent data sets retrieved from the literature and discussed.