Unsaturated Rankine soil pressure analysis under unsteady seepage

Abstract:

Changes in water content alter soil mechanical properties. Current engineering theories for earth pressure calculation mainly use saturated soil theory. This study investigates unsaturated soil pressure under seepage effects with dynamic soil-water characteristic curves. Unsteady seepage is considered. The Richards equation during seepage process is solved. A theoretical solution for suction considering dynamic soil-water characteristic curves is obtained. Suction distribution patterns are analyzed. Using the suction solution with dynamic effects, the Rankine earth pressure equation for unsaturated soil under seepage is derived. The equation helps analyze dynamic effects on unsaturated soil pressure distribution. The theoretical earth pressure solution is applied to foundation pit support structures. Numerical software simulates earth pressure changes on support structures during rainfall infiltration with different intensities. Safety factors of support structures are calculated using unsaturated soil theory. Results show: Dynamic effects increase active earth pressure and decrease passive earth pressure. Larger suction leads to more significant differences. Under rainfall infiltration, dynamic effects make active earth pressure on support structures smaller than static effects. Faster infiltration rates cause greater pressure differences. Safety factors calculated by unsaturated soil theory exceed those by saturated soil theory. Considering dynamic effects reduces safety factors, indicating rainfall infiltration increases foundation pit instability risks.