Centrifugal model tests and numerical simulation of three-dimensional space effect of deep and large foundation pit under the confined water level fluctuation

The deformation of foundation pit is considered as a typical three-dimensional (3D) space problem, but it can be simplified as a plane strain problem under specific conditions. Through 3D centrifugal model tests of a foundation pit, the deformation laws of the middle and the corner of the long side of the foundation pit were achieved under the fluctuation of the confined water level. Then 3D numerical simulation was further carried out, and the obtained results were compared with the results from the centrifugal model test. The numerical method was also used to analyse the effects of foundation pit length, excavation depth, confined water level and foundation pit area on the 3D space of foundation pit. The results showed that the corner effect was verified by the horizontal displacements at different sections of the ground wall and the surface settlement outside the foundation pit. When the length of the foundation pit was more than six times the excavation depth in Yangtze River Terrace I, the middle section of the foundation pit was basically in the plane strain state. As the excavation depth increased, the plane strain ratio increased significantly. However, the increase rate slowed down when the depth was greater than 25 m. The corner effect was more obvious with increasing confined water level, and the plane strain ratio reached 0.46 when the level exceeded 3 m. The research results provide the basis for the design and construction of the deep and large foundation pit in the typical binary structure strata of the Yangtze River Terrace I.