Elasto-analysis for a deep tunnel considering intermediate stress and strain-softening behavior

To study the role of the intermediate stress on the bearing capacity in a circular tunnel,a finite difference method,which is used to calculate the strain-softening behavior of rock masses considering the effect of the intermedi- ate stress,is proposed based on unified failure criterion and non-flow associated flue. The accuracy of the proposed method is investigated by example verification. Due to the significant effect of mechanics model on the ground response curve,three different mechanics models,i. e. ,elastic-perfect plastic model ( EPP ),brittle plastic model ( BP ) and strain-softening model (SS),are used to study the effect of intermediate stress and support force on the plastic radius, the stress distribution in the plastic zone and the displacement at the tunnel wall,respectively. The results show that the plastic radius and the displacement at the tunnel wall calculated by EPP are much less than those by other me- chanic models. Therefore, the EPP is suggested to be cautiously used because it does not consider the weakening strength of rock masses in the plastic zone. The intermediate stress can restrain the development of the plastic radius and the displacement at the tunnel wall,especially for EB under no support force condition. This restraining effect of the intermediate stress on the plastic development decreases with the increase of support force. The confining stresses on the boundary of elastic-plastic zone and the boundary of softening-residual zone are not related to support force at the tunnel wall,but decrease with the increase of intermediate stress coefficient.