Face-Stability Analysis of Tunnels Excavated below Groundwater Considering Coupled Flow Deformation

Abstract

In this study, using the kinematic approach of limit analysis, a new numerical model was developed to investigate the effect of the coupled flow deformation on tunnel face stability. By incorporating the innovative mesh-dividing optimization technology with the principle of generating a three-dimensional (3D) rotational failure mechanism into a customized program of linear interpolation, the pore-water distribution in the stage of the global failure ahead of the tunnel face determined by FLAC3D was interpolated on the 3D rotational failure mechanism. The support pressures predicted by the developed model improved the existing upper-bound solutions by at least 14.2% for the case of slight cohesion soils but made little difference with the existing upper-bound solutions for high cohesion soils. The support pressures predicted by the developed analytical method were in close agreement with those from numerical simulations and in situ data. The results showed that the critical face pressures increased linearly with increasing water table elevation. Several design charts are provided for parametric analysis, which can be directly used by tunnel engineers in the evaluation of face stability.