Abstract:A statistical damage numerical model was employed to investigate the fracture mechanism of underground openings under triaxial stress state. A three-dimensional tunnel model was established by considering rock heterogeneity described by Weibull distribution. The strength reduction method was introduced into the numerical model to achieve progressive failure of surround rock mass by decreased rock strength gradually. The fracture patterns and safety factors of the underground openings in different stress fields were also obtained quantitatively. Failure patterns under different lateral pressure ratios and axial stresses were analyzed by varying the lateral pressure ratios of the maximum principal stress to the minimum principal stress. The influence of intermediate principal stress on the opening stability, and the stress condition of zonal disintegration phenomena were discussed. The results showed that the failure behavior of the surrounding rock mass was complicated due to the various triaxial stress states. Both lateral pressure ratio and axial stress had significant influences on the tunnel failure patterns. When the direction of tunnel axis is parallel to the maximum principal stress,the zonal disintegration of underground openings appeared because of large axial stress,and the ruptured zone resulted in tensile strain concentration. The numerical model can obtain the fracture patterns and evaluate the tunnel stability,which will be much helpful for revealing nonlinear deformation and failure behavior of rock tunnels in tunnelling engineering.
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