Abstract:The seepage of ultra-deep diaphragm wall joints is one of the typical problems in the deep excavation in Shanghai soft soil area, which affects the safety of foundation pit construction and the quality of the whole project. In this study, combining with a deep excavation project of North Cross Channel in Shanghai, PLAXIS 3D finite element software was used to calculate and analyze the overall deformation of the diaphragm wall under different working conditions during the excavation of the foundation pit, and to find out the relationship between lateral displacement and joint opening leakage of the wall. (1) When the excavated depth is greater than 12m or 20m, the growth rate of lateral displacement is significant. The maximum horizontal displacement of the diaphragm wall occurs near the middle point and gradually decreases to both sides, which is mainly caused by the space effect of the foundation pit corner. (2) The dangerous point of underground wall joint opening leakage does not occur at the maximum lateral deformation at the midpoint of the pit, but between the middle of the pit edge and the corner, and nearer to the corner. (3) Even for the small-sized ultra-deep excavation, when the excavated depth is larger, the displacement of the long side still increases significantly compared with the displacement of the short side. The conclusions of this paper are of guiding significance for the diaphragm wall deformation and leakage control in ultra-deep excavation.
