Face Stability Analysis of EPB Shield Tunnels in Dry Granular Soils Considering Nonuniform Chamber Pressure and a Dynamic Excavation Process

Abstract

The support pressure at the tunnel face of earth pressure balance (EPB) shield machines is usually assumed to be uniform from the crown to the invert, which is a notable simplification of reality. In this study, the effects of nonuniform soil pressure in the chamber and the dynamic shield excavation process on the face stability are investigated using a three-dimensional (3D) discrete element method (DEM) model. The behavior of the excavation face subjected to different overburden depths and ground conditions is assessed and also compared with previous research. The results show that the limit face pressure and failure zone is overestimated without considering the nonuniform soil pressure in the chamber. When considering the nonuniform soil pressure in the chamber, a partial failure mode is observed in granular soil that is characterized by flow originating at the upper part of the excavation chamber and limited flow ahead of the face. This effect has a nonnegligible influence on face failure mode and the arching effect, especially near the invert, which is in contrast with the findings associated with global failure modes considered in previous studies.