Model tests on failure characteristics of red weak surrounding rock of shallow buried tunnels

During the construction of shallow buried tunnel with weak surrounding rock mass, large deformation and landslide accident are likely to occur, which has become one of the difficult problems for tunnel construction. The model tests are performed to study the deformation failure modes as well as the stress disturbance characteristics of red weak surrounding rock of Nanhua No.1 Tunnel project of Guangtong-Dali Railway. The results show that there are cracks with an angle of 45°+φ/2 to the horizontal plane at both sides of the tunnel waist after tunnel excavation, and these initial cracks gradually extend upwards to the crown, eventually forming a collapse arch with a height of approximately 0.5 times the tunnel diameter. Moreover, the tunnel excavation will cause the stress redistribution of surrounding rock stress, forming a circle of stress-reducing zone around the tunnel, and at the outside is the stress increase zone, while the rock mass collapse area is mainly located in the stress-reducing zone. In order to reduce the collapse risk, on the one hand, the exposed surrounding rock should be supported as one whole ring as soon as possible. On the other hand, the rock mass in the stress-reducing zone should be appropriately reinforced to make full use of its self-supporting capacity. These findings can be used to guide the design and construction of this project and may provide reference for future similar projects.