Numerical simulation of passive failure of underwater shield tunnel excavation face in sandy soil layer

Based on the Mohr-Coulomb strength criterion and uncorrelated flow rule, Abaqus is used to simulate the passive failure of the excavation surface of underwater shield tunnel in sandy soil layer, and influences of the buried depth ratio C/D, height of overlying water level H and friction angle φ in sandy soil on the surface displacement are analyzed. The failure mode of the soil in front of the excavation face is also discussed. The results show that the support pressure of standard excavation face is related to C/D, sand φ, and there is a positive correlation between them; the surface displacement is greatly affected by the change of C/D, and when C/D increases from 0.8 to 1.5, the maximum longitudinal and transverse displacement decrease by 80% and 86% respectively; hydrostatic pressure will only limit the development of lateral surface displacement and has little effect on longitudinal surface displacement; when C/D is small, the passive failure mode presents an inverted pyramid shape extending to the surface, which belongs to overall failure; when C/D increases to 4.3, the soil arch cannot reach the ground surface, which belongs to local damage.