Study On Failure Mode Of Tunnel Face And Reinforcement Mechanism Of Advanced Bolt

Taking the method of full face excavation-NITM as background, make a study on failure mode of tunnel face by full face excavation. It provides a new analysis mode for the stability of tunnel face. Then the stability coefficient of tunnel face was analyzed based on the failure mode. Using bolt-soil interactional model, this paper made a research of reinforcement mechanism of advanced bolt. Then, analyze the influence of parameters for reinforcement effect.At first, based on result of experiment, four-block failure mode was built using limit equilibrium method. Then take upper bound theory to calculate the stability coefficient under different conditions. When the gravity of soil was not considered, the upper bound of stability coefficient of four-block mode was larger than that of Davisˊmode. With the increasing of gravity of soil, the upper bound of stability coefficient of four-block mode was closer to the lower bound than that of Davisˊmode. It indicated that the four-block mode is more suitable for the tunnels with large gravity or large diameter. Considering the influence of internal friction angle for the stability coefficient, the value of stability coefficient increased with the increasing of the value of internal friction angle. The internal friction angle has a big impact on the stability of tunnel face. It should be considered when the stability of tunnel face is analyzed.Then, build bolt-soil interactional model and analyze the reinforcement mechanism of advanced bolt on basis of extrusion deformation of the tunnel core soil. Reinforcement coefficient k was introduced to calculate the reinforcement effect of bolt and analyze the influence of parameters for reinforcement effect. The results show that the reinforcement effect of advanced bolts has relationship with length of anchorage section, elasticity modulus of bolt, cross section of bolt, density of bolts, elasticity modulus of soil and deformation of soil. Combine theory analysis and numerical fitting to analyze the relationship between the length of anchorage section and the length of bolt. When the bolt and soil have no common deformation, analyze the reinforcement mechanism and calculate the length of slippage.At last, Tunnel excavation process was simulated by finite difference software FLAC3D, and then detect the failure mode of tunnel face. On basis of extrusion deformation and difference extrusion deformation of tunnel face, the impact of parameters of bolt and soil was analyzed.The results of research provide a new analysis mode for stability of tunnel face and theory guidance for parameter design and reinforcement effect evaluation of advanced bolt.