An analytical model for face stability of tunnels traversing the fault fracture zone with high hydraulic pressure

Abstract

The issue of tunnel face stability traversing the fault fracture zone with high hydraulic pressure has been addressed based on a new three-dimensional limit equilibrium model. First, the finite element numerical simulation is conducted to reveal the effects of the differences in permeability coefficient of strata on both sides of the geological interface on the distribution of seepage flow field nearby tunnel face. With this discovery, an existing universal approximate formula for hydraulic head nearby tunnel face is modified to accurately calculate the hydraulic head distributions under this scenario. Second, introducing the effect of geological interface, a new limit equilibrium model that consists of a trapezoid and a prism is proposed. The distributed loading exerted by the prism upon the trapezoid is deduced by considering the effects of seepage force and geological interface. Then, limit support pressure is derived according to the limit equilibrium state of the trapezoid. Finally, the comparison of the predicting results of the proposed limit equilibrium model with the results of the numerical simulations and the existing failure mechanism is performed, which indicates that the proposed trapezoid-prism model can well predict the tunnel face stability traversing the fault fracture zone with high hydraulic pressure.