Tunnel Face Excavation Stability in Unsaturated Media Based on Limit Analysis Method

In the present work، in the framework of limit analysis method، with consideration of a 3D continuous failure mechanism، stability of tunnel excavation face in unsaturated media was studied. Governing kinematic equations were adapted for unsaturated conditions with introducing unsaturated form of Mohr Coulomb failure criteria. Afterward، a set of parametric analyses، in different form of suction distribution and tunnel geometry were performed. Based on obtained results، matric suction and its distribution influences considerably on tunnel face stability so that، increase in matric suction leads to decrease in limit pressure exerted on tunnel face. In the final section of paper، finite elements numerical analyses in the same conditions of material and geometry were executed. The results indicate that limit analysis predict a limit pressure more than finite elements method.