Investigation on elastic–plastic deformation and mechanical failure of varied-moisture expansive soil subjected to dry–wet cycles

Understanding expansive soil behavior under variable environmental conditions is crucial for environment and engineering contexts. This study investigates the deformation mechanism and mechanical behaviors of expansive soil with varied moisture contents under dry–wet cycles. Through theoretical analysis and laboratory tests, we first analyzed the elastic–plastic behavior of expansive soil under dry–wet cycles and then explored the elastic–plastic deformation, fracture characteristics, and mechanical properties therein. Results indicate that the soil aggregates evolve through the four stages of stable, compact, loose, and damaged structures under the dry–wet cycles. The swelling–shrinkage deformation consists of elastic and plastic components, and the magnitude of elastic expansion is always smaller than that of plastic expansion. Meanwhile, the cracks develop with the increased water content and the increased number of cycles. The aperture of the induced cracks increases as the water content increases. Accordingly, the shear strength sequentially decreases with the increasing number of cycles and the increasing moisture content. The decrease in shear strength with the increasing cycles is primarily due to structural damage accumulation followed by the reduction of cohesion, while the decrease with increasing water content is primarily due to the reduction in matric suction and the increased lubrication between soil particles and aggregates. In addition, the cohesion decreases with the increasing moisture content and the increasing number of cycles. However, the friction angle decreases only with a clear increase in the number of cycles, showing less sensitivity to dry–wet cycles in general.