Calculation of support forces at the excavation face of a shallow buried shield tunnel in dense sandy soil considering construction disturbances

Abstract

ABSTRACT Too little support force at the palm surface during shield excavation can lead to destabilization of soil before the excavation face and cause ground subsidence. Construction disturbances during excavation can affect the mechanical properties of the surrounding soil, which cannot be ignored when determining the needed support force at an excavation face. Based on the Mohr – Coulomb yield criterion, the collapse of dense sandy soils before the excavation face of shallowly buried shield tunnels is simulated using PLAXIS 3D to determine the collapse mode. Furthermore, the prismatic body in the traditional 3D wedge model is modified to an inverted elliptical-truncated cone with a certain inclination so that the collapse zone is closer to real sliding soils, and the disturbance ratio r is introduced as an index to consider a construction disturbance. The expression of the active limit support force with respect to wedge inclination is derived, and the maximum support force is determined by trial and error to be the minimum support force needed. The results of the modified 3D curved model are in good agreement with the numerical simulation results, as well as the results of theoretical methods and model tests.