Face Stability Analysis for Tunnels under Steady Unsaturated Seepage and Inhomogeneity Conditions

In the field of tunnels, the stability of tunnel faces is generally considered in dry, saturated and homogeneous soils. However, the actual condition of some soils has been found to be inhomogeneous, with unsaturated seepage. In this paper, an analytical method is applied to estimate the safety factor when the supporting force at the tunnel face is zero under steady unsaturated seepage and inhomogeneous conditions. This method combines kinematic limit analysis techniques with strength reduction techniques; an efficient stress formulation utilizing suction stress is employed to determine the apparent cohesive force to obtain the solution of the steady unsaturated seepage problem, and indicators of soil inhomogeneity are attributed to the effect on cohesion. A 3D log-spiral collapse mechanism is used to find the zero supporting pressure and determine the safety factor through an iterative method. This paper analyzes the effect of variations in the unsaturated parameters, inhomogeneity parameters and tunnel dimensional parameters on the stability of the tunnel face.