Elasto-plastic solution and saturation response of cylindrical cavity expansion in unsaturated soil under constant suction

Abstract:

The stress-strain characteristics and saturation response of cavity expansion under constant suction in unsaturated soil were investigated. The semi-analytical drained solutions were derived for cylindrical cavity expansion in unsaturated soil based on the unsaturated critical state model (UCSM), the soil-water characteristic curve (SWCC) considering hydraulic hysteresis, and the nonlinear model of saturation varying with void ratio under constant suction. According to the equilibrium differential equations of soil elements around the cylindrical cavity, an auxiliary coordinate was introduced considering boundary conditions, and the problem was solved by first-order differential equations with three principal stress components, void ratio, and saturation as basic unknowns. The solutions fully considered the influence of matric suction and over-consolidation ratio on the expansion response, and explored the stress distribution and volume change in soil around the cylindrical cavity, as well as the saturation evolution law during the expansion process. Results show that the soil exhibited the characteristics of suction hardening during the cylindrical expansion under constant suction and the suction hardening phenomenon tended to be stable with the increase in suction. The saturation of soil at and around the cavity wall changed significantly during the expansion process and was greatly affected by suction. For soil with lower suction, the saturation was mainly affected by the water content change. While for soil with higher suction, the saturation was mainly affected by the void ratio change. This solution can well capture the saturation response of unsaturated soil under different stress histories and hydraulic states, which can provide guidance for the interpretation of in-situ tests such as cone penetration tests in unsaturated soil.