Face Stability Analysis of Tunnel with Pipe Roof Reinforcement Based on Limit Analysis

Based on the kinematic method of limit analysis and the shear strength reduction technique, the three-dimensional model for expressing the tunnel face stability with pipe roof reinforcement was established. For a typical example, the solutions computed by the proposed approach were compared with the results given by wedge model, trapezoid wedge model and centrifugal-model test. The proposed approach was also employed to study how the cover depth of tunnel, tunnel diameter and soil parameters affect the support pressure and safety factor of tunnel face. It is shown that the calculation results of limit analysis is smaller when compared with that by wedge model and trapezoid wedge model, and also more closer to the results of centrifugal-model test. It is also found that for the relative depth investigated ( / 0.5 ~ 8H D =), cover depth has a little influence on the stability of tunnel face for a given diameter, but a good linear relationship exits between safety factor and tunnel diameter. The linear and quadratic formulas are able to account for the influence of cohesion and friction angle of soil on limited support pressure of tunnel face, respectively. The analytical results of tunnel face stability also reveal that the safety factor of tunnel face with pipe roof reinforcement is about 1.05~1.20 times of that without pipe roof reinforcement. The effect of pipe roof reinforcement on tunnel face stability is not significant