Numerical modeling of volumetric behavior of unsaturated expansive soil under wetting and drying cycles

Expansive soils undergo volumetric changes due to moisture variations as a result of soil-atmosphere interaction. In this study, the moisture-induced volumetric changes in unsaturated expansive soil under wetting-drying cycles were modeled. The variations in moisture content during wetting and drying cycles were analyzed for a specific type of expansive soil using one-dimensional coupled hydro-mechanical analysis within the framework of the Barcelona Expansive Model for expansive soils (BExM). The modeling was performed utilizing the finite element method in CODE_BRIGHT. The volume changes in the soil due to wetting and drying cycles, associated with changes in moisture and suction in the unsaturated zone, led to repetitive swelling and shrinkage deformations in the expansive soil. The effects of these variations were significantly more pronounced in the initial cycles, and after several cycles, the cyclic behavior within a specified range persisted for the same defined range of suction changes. However, this trend shifted towards more elastic behavior at lower rates of suction changes. Furthermore, the effect of surcharge on the volumetric behavior of swelling soil during wetting and drying cycles was investigated. As the surcharge increased, the magnitudes of cyclic deformation decreased. By comparing soil deformation under two different surcharge, elastic behavior was observed in the first three initial cycles for higher surcharge, followed by irreversible deformations. For lower surcharge, irreversible deformations were observed after the first cycle until equilibrium was reached after several wetting and drying cycles.