Three-dimensional blow-out stability analysis of shield tunnel face in anisotropic and heterogeneous soils

Many published experimental tests and field observations have shown that blow-out failure is potentially more likely to happen during the excavation of shallowly buried tunnels. However, limited research has been con-ducted to assess the three-dimensional (3D) blow-out stability analysis of shield tunnel faces, especially in anisotropic and heterogeneous soils. To resolve this shortcoming, a 3D blow-out failure mechanism is developed to make it possible to incorporate the influences of the anisotropies and heterogeneities of the soil properties into the determination of the limit blow-out pressure and the limit failure surface in the framework of upper-bound limit analysis theory. For verification purposes, the proposed method is tested through comparisons with existing analytical solutions and numerical results for some special cases. Then, the effects of the anisotropic and het-erogeneous soil properties on the normalized limit blow-out pressure and the limit failure surface are presented and discussed. Finally, applications of the proposed method to blow-out stability analyses considering spatially variable soil properties and inclined ground surfaces are performed to illustrate that the proposed method has the potential to serve as a benchmark for the blow-out stability of tunnel faces under complex geological and geometrical conditions.