Abstract: From the viewpoint that rock is a heterogenic material, by introducing microscopic elements in microscopic level, using unit constitutive model based on damage mechanics and statistics theory and adopting RFPA2D, an analysis software for rock fracture process, analysis is made of the deformation failure mode and characters of the tunnel excavated in rock mass cut by bedded weak structural planes at different dip angles, the displacement and stress change at the key points on tunnel surface as well as the safety margin of the tunnel. It will be of great theoretical and practical significance to the further understanding of the failure and instability mechanism of the tunnel in weak structural planes and to the adoption of effective strengthening measures.

Key words: Structural plane, Tunnel, Failure, Numerical simulation