Failure Mechanism of Face for Slurry Shield-Driven Tunnel in Sand

摘要

To achieve the failure mechanism of face for slurry shield tunnel in sand stratum, a model test device for shield excavation with ideal slurry film was developed. The active failure processes of tunnel excavation face in dry sand stratum for different densities and cover depths were achieved through model test and two-dimensional particle flow code (PFC~(2D). Furthermore, soil deformation, failure mode and soil arching effect of tunnel excavation face were revealed. The results show that the face deformation can be divided into three stages in relation to the support pressure and the excavation face has been failed in third stage. The density of sand has a great influence on the failure mode of excavation face. The failure mode in dense condition is a combination of a wedge with slip arc and a prism chimney, while in loose condition it is a relatively dispersed "trumpet" shape failure zone. However, the cover depth has a negligible effect on the failure mode. In dense sand stratum, a loose failure zone was formed in front of the excavation face and a soil arch was formed above it. The soil arch developed continuously above the tunnel crown to the ground surface. The limit support pressure calculated by PFC~(2D)(two-dimensional particle flow code) increases with the cover depth, which is consistent with the observations in model tests.