Shear and slip failure mechanism and control of tunnels with weak surrounding rock

The slip-line field of homogeneous elastic-plastic surrounding rock and the ultimate load which containes fracture morphology parameters are obtained by using the slip-line field theory. The effects of friction angle, cohesion and support resistance on the stability of tunnels are discussed. The study shows that with the impact of stress redistribution of excavation, shear failure occurres in the surrounding rock and distinct shear slip-lines are formed. The shear slip-line field of surrounding rock of circular tunnel is composed of two families of oblique crossing concentric logarithmic spirals which have the same pole in the center of the tunnel as other parameters except for different directions of rotation. The friction angle, cohesion of rock and support resistance are the main influential factors of shear slip failure of the surrounding rock and also the key points of controlling the stability of the tunnel. Based on the theoretical analysis, the causes of large scale deformation and failure of some coal mine auxiliary shafts are analyzed. The resistance of shear failure and block slip of the surrounding rock is proposed as the core technology of the support scheme, which is finally proved to be efficient in practice.