Numerical Simulation Study on the Failure Process of Overlying Marine Soft Soil during Vertical Jacking

Based on the on-site data of vertical pipe jacking construction, a numerical model of vertical pipe jacking was established by using the particle flow code PFC2D. The failure process of the overlying marine soft soil layer and the jacking force were analyzed. The numerical model was verified to be reasonable by comparing the jacking force obtained from the field measurement and theoretical calculation. Then, the influence laws of the overburden depth, pipe diameter and pipe spacing on the failure process of the overlying marine soft soil layer were discussed from a mesoscopic perspective. The results show that: (1) During the pipe jacking process, the failure of the overlying soil layer mainly goes through the following processes: Compression at the bottom of the soil layer leads to shear failure → oblique cracks appear around the pipe → cracks expand to form voids → redistribution of the soil layer above the cracks → filling of the voids → new cracks are generated; (2) In the numerical simulation of vertical jacking, the failure surface of the soil layer has obvious nonlinear characteristics, and the error between the simulated maximum jacking force and the measured value is within 9%, which verifies the rationality of the numerical model; (3) With the increase of the overburden depth, the top failure range of the overlying marine soft soil layer increases linearly; (4) When jacking through a layer of silty clay interbedded with silt, the failure range of the surface soil is in a power function relationship with the pipe diameter, and its influence on the surface failure range is much smaller than that of the overburden depth; (5) The failure range of the overlying soil caused by jacking a single pipe was determined, and a reference formula for the minimum pipe spacing in pipe layout was given. The above numerical simulation results have reference value for the optimization of vertical jacking construction technology in the sea area and the layout of pipe spacing.