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

Abstract

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. Collapsible and expansive soils cover about one-fifth of the Earth’s surface. These soils are characterized by high deformability once a near-saturation condition is approached. As a result, the corresponding hydraulic conductivity can be subject to sever variations because of significant microstructural modification induced after inundation or hydration. However, most of the measuring devices and modeling frameworks fail to take into account the saturation-induced volume changes of problematic soils in estimation of permeability versus void ratio function. Therefore, the significance of volumetric strain during the saturation procedure was first revealed and highlighted through conducting 36 permeability experiments in a low-compliance triaxial permeameter on both collapsible and expansive soils, with various deformation potentials in response to full saturation. Afterward, new models pertaining to both types of soils were developed based on the Kozeny–Carman model with two additional physics-based parameters reflecting the deformation tendency of a given soil. Indeed, the merit of the new modeling framework is the incorporation of collapse and swell potentials into the void ratio function, which can be easily measured with a conventional oedometer cell. Eventually, the proposed modeling approach was validated against measurements conducted in this study as well as several data sets retrieved from the literature.