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.

Seepage force is simplified as seepage volumetric force in the stress field along the radial direction. Out-of-plane stress and seepage force are incorporated, and the theoretical solutions for stress, displacement, and plastic radius of a circular opening for the elastic-brittle-plastic and elastic-plastic rock mass are proposed based on the Mohr–Coulomb (MC) and generalized Hoek-Brown (HB) failure criteria. The presented solution and Wang’s solution (2012) are compared, and the corrected version of the proposed method is validated. Numerical examples of the proposed method based on the MC and generalized HB failure criteria reveal that the distributions of stress and displacement in the surrounding rock of the tunnel are significantly influenced by seepage force and out-ofplane stress. Displacement and plastic radius when seepage force and out-of-plane stress are considered are larger than those when the seepage force is not considered; the regulations of stress, however, run opposite. The results of displacement and plastic radius based on the generalized HB failure criterion are larger than those based on the MC failure criterion.

Similarity Solution for the Synchronous Grouting of Shield Tunnel Under the Vertical Non-Axisymmetric Displacement Boundary Condition - Volume 9 Issue 1 - Jinfeng Zou, Songqing Zuo

The effect of out-of-plane stress on theoretical solutions of stress, displacement, and plastic radius for a circular tunnel were studied by using the generalized Hoek–Brown (HB) failure criterion and nonassociated flow rule in elastic–brittle–plastic rock masses. A technique of using equivalent Mohr–Coulomb and generalized HB strength parameters was adopted to compare results of the developed method and published results. The presented solution was validated by existing theory. The results of the developed method were found to be larger than those previously published, which were determined through programming.