Stability Analysis of 3D Deep Tunnel Face under Steady Seepage Flow Condition

Abstract

The instabilities of tunnel face may occur while shields advance through the rivers or region rich in water. It is of significance to attach the importance to the estimation of face stability during the tunnel excavation. Thus, this paper adopted a three-dimensional (3D) rotational mechanism to analyze the face stability under steady seepage flow field with the aid of the kinematic method in the context of limit analysis. The hydraulic head that derived by fitting the results of trial and error is employed herein to portray the steady seepage flow field. With the aid of a double integration method, the work rate induced by seepage forces acting on the soil skeleton is calculated and accordingly a closed-form solution of support pressure is derived based on the work balance equation. By comparing with the literature, one can validate the rationality and correctness of the present results. The research shows that the proposed method based on rotational mechanism provides a better upper bound estimation, when under seepage condition, the influence of internal frictional angle on the stability of the excavation face is not always monotonic and the influence of head difference on the support pressure is significant. Finally, the normalized stability charts are provided for a quick assessment for practical use during tunnel excavation in water-rich stratum.