Numerical simulation of influence of section geometry on surrounding rock stability of arch tunnel with straight wall

Based on the Mohr-Coulomb strain softening model, the nonlinear CWFS criterion of friction strengthening and cohesion weakening is adopted, and the deterioration behavior of tensile strength and stiffness modulus caused by tensile-shear coupling yield of intact rock mass is considered. Through two different modeling methods, the influence of geometric characteristics of straight wall arch tunnel section on the failure of surrounding rock and rock-burst is simulated. The results show that the geometric characteristics of tunnel section have obvious influence on the stability of surrounding rock. The rise-span ratios are 0.5, 0.297 and 0.16, and the height of straight wall is 0.875 m. The plastic zone, rock-burst zone, tensile yield zone and shear strain localization zone of surrounding rock decrease with the decrease of rise-span ratio. When the rise-span ratios are 0.5, 0.297 and 0.16, and the vertical wall heights are 0.875 m, 1.23 m and 1.47 m, respectively, the plastic zone, rock-burst zone, tensile yield zone and shear strain localization zone of surrounding rock increase significantly with the decrease of rise-span ratio. When the rise-span ratio is 0.16 and the straight wall height H4 = 1.47 m, the maximum shear strain increment is about 10-2 , which is an order of magnitude higher than other schemes. According to Russense rock-burst criterion and shear strain localization results, the rock-burst units are mainly concentrated in the top and bottom of the tunnel section, which is consistent with the rock-burst position recorded in the field tunnel.