Abstract: The horizontal and lateral displacements of pile-cap and the ground settlement of the surrounding soils of a foundation pit of a subway station in sandy soil were investigated based on the in-situ monitoring data. The changing rules of the displacement of the inner supporting system and the deformation of the surrounding soils with excavation time and excavation depth were obtained. A two-dimensional finite element model was built to analyze the internal forces of the supporting structures as well as the stress redistribution in soils behind those piles. Numerical results agree well with the in-situ monitoring data. Results indicate that the horizontal displacement of the pile-cap in the long side direction of the foundation pit is three times than that in the short side direction; the maximum lateral displacement of the piles occurs at 1/2H(H is the depth of the foundation pit). The range of the ground settlement induced by excavation and drainage is 3H. The largest deformation in the surrounding soil is located 22m away from the excavation edge(0.82H~0.96H). It is found that the inner supporting system can effectively improve the stability of the foundation pit.

Key words: sandy soil, deep foundation pit, stability, evaluation, mechanical effects