A SEMI-ANALYTICAL METHOD FOR EMBEDDED DEPTH STABILITY OF STABILISING PILES IN FOUNDATION PIT CONSIDERING UNSATURATED EFFECTS

Abstract

The soil bears pronounced unsaturated features as the foundation pit being larger and deeper. This study aims to investigate the influence of suction on the stability evaluation of foundation pit projects. In the category of upper bound limit analysis theorem, a straight and logarithmic spiral line combined mechanism is employed to simulate the slip surface and a horizontal slice method is advised to formulate the energy balance equation. The errors between this paper and the benchmark solution are generally less than 2.0% when the soil mass is discretized into 200 layers, indicating the satisfactory performance of the horizontal slice method and the agreement with engineering requirements. Parametric analyses are conducted and the findings indicate that the stability of foundation pit in fine-/coarse-grained soils would be underestimated/overestimated when suction is not considered in analyses. The foundation pit in fine-grained soils is more sensitive to water infiltrations. Factor of safety (FOS) drops 34.90% for SWCC-D and 16.40% for SWCC-C. For deeper foundation pits, FOS increases nearly linearly with respect to the embedded depth ratio H₂/H and the brace height ratio H₁/H. The findings provide insights into the role of suction on the foundation pit stability. This semi-analytical method can serve as an effective tool for stability analyses of unsaturated foundation pits.