Influence of Parameter Variation of Saturated–Unsaturated Soil on Deformation and Stability of Foundation Pit

The soil–water interaction of unsaturated soil has a significant impact on the characteristics of the soil. Capillary action makes the distribution range of unsaturated cohesive soil deep, and the effect of matric suction changes the characteristic parameters of the soil, affecting the deformation and stability of the foundation pit. In this paper, the theory of zonal shear strength of saturated–unsaturated soil is established. The physical and mechanical initial parameters of soil are obtained through tests. The deformation and slope stability of foundation pit are studied by finite element method. The theory is applied to the deformation and stability analysis of the foundation pit of the drainage pump station in Lanxi. When the excavation reaches a depth of 5 m, the error between the monitoring value of the horizontal displacement of the top of the foundation pit and the simulation result of the model is within 10% when considering the change of the unsaturated soil characteristic parameters; When the excavation reaches the depth of 9 m, considering the change of unsaturated soil characteristic parameters, the extreme value of stability coefficient of the foundation pit slope before and after adding steel support increased by 16.0% and 6.7% respectively. The theoretical model and numerical simulation results of saturated unsaturated soil in this paper are more consistent with the actual situation. The research results can be applied to the slope stability analysis of foundation pit excavation engineering.