Effect of the seepage flow on the face stability of a shield tunnel

Abstract

To assess the face stability of a shield tunnel excavated in saturated soils under steady seepage flow condition, both numerical simulation and theoretical analysis are carried out. Based on the characteristics of the hydraulic head distribution, an analytical solution for the hydraulic head distribution ahead of tunnel face in the homogeneous and isotropic ground is proposed. And based on the upper bound theorem of the limit analysis, the analytical head equation is introduced into the 3D rotational rigid block collapse mechanism to take into account of the effect of the seepage flow. The comparisons show that the presented method agrees well with the numerical analysis and other existing studies. Finally, an analytical solution for the hydraulic head distribution ahead of tunnel face considering the permeability anisotropy is also presented and discussed. It is suggested that the neglect on the permeability anisotropy of soils may lead to an overestimate on the required face pressure.