Stability Analysis and Failure Mechanisms of Jointed Rock Tunnel

In the past, only displacement, stress, size and distribution of plastic zone can be obtained when analyzing the stability of jointed rock tunnel. Neither the location and range of the failure surface could be found, nor the quantitative critera of safety factor be obtained. Quantitative analysis of the stability of a jointed rock tunnel is deduced in this paper by model test and numerical analysis. Failure state and safety factor of the jointed rock tunnel are calculated by using FEM strength reduction. The results show that joint obliquity α has a greater impact on the location of failure surface. If α=0°, failure surface distributes symmetrically on both sides. If α=30° and 45°, failure surface rotates with the change of joint obliquity correspondingly and distributes in the up-down parts of the joint. If α≥60°, failure surface transfers to the vault and the foots of the sidewall mainly because of gravity. In particular, if α=90°, a failure surface can be formed in the middle of vault. The safety factor results show that safety factors reduce in different degrees in jointed rock tunnel compared with homogenous tunnel; but, joint obliquity has little impact on the safety factor. With the reduction of joint spacing and strength, the safety factor decreases.