Limit analysis for 3D stability of slurry trench under unsaturated seepage conditions

To address stability issues in constructing underground diaphragm wall trenches, we applied an upper-bound limit analysis method using a three-dimensional rotation failure mechanism. This approach considered unsaturated stable seepage conditions. We derived the safety factor expression through an energy balance equation and employed a genetic algorithm to find the minimum safety factor and critical slip surface. We analyzed the impact of various parameters on trench stability under unsaturated seepage conditions. Our results show that 3D analysis yields higher safety factors compared to 2D analysis. Safety increases with slurry-to-soil density ratio, cohesion, and friction angle, but decreases with reduced slurry depth relative to trench depth. Suction in unsaturated soil enhances trench stability, with its effect varying based on seepage conditions and soil types. Additional load increases decrease the safety factor, especially with greater three-dimensional effects. Reducing slurry height expands the critical slip surface area, with different seepage conditions significantly affecting clayey trenches but having a negligible impact on sandy ones. These findings provide valuable insights for designing underground diaphragm wall trenches in unsaturated seepage conditions.