Mechanism Of Unstable Shear Failure Of Discontinuities Based On Discrete Element Method

With the increase of deep underground projects such as tunnel excavation or underground mining,the disasters caused are becoming more and more frequent.Underground excavation may cause shear failure of adjacent discontinuity.Such shear failure may be stable or unstable.Especially in deep,high-stress underground environments,it is likely that violent and unstable shear failure will be accompanied by a large amount of energy release,which will cause huge damage to engineering and staff.Predecessors have done a certain amount of research on the shear failure of discontinuities with UDEC software,but they have not considered the heterogeneity of discontinuities.The natural discontinuity surface is rough and uneven,and the shear behavior of the discontinuity will be affected by the geometry of the discontinuity.In this paper,combined with previous excellent research results,using UDEC and continuously yielding joint model,and considering the heterogeneity of the parameters of discontinuity,further study on shear failure.The simulation results of the double shear test model show that: in the shear failure(stable and unstable)of homogeneous discontinuity,the peak shear stress of joint of the discontinuity decreases from left to right.In the unstable shear failure of homogeneous discontinuity,the degree of unstable failure of joint of the discontinuity increases from left to right.In the shear failure(stable and unstable)of heterogeneous discontinuity,the size of the parameters at joint of the discontinuity directly affects the magnitude of the peak shear stress of the joint.In the stable shear failure of heterogeneous discontinuity,the post-peak stiffness of the average shear stress-displacement curve of the discontinuity decreases as the homogeneity coefficient decreases.In the unstable shear failure of a heterogeneous discontinuity,the size of the parameter at joint of the discontinuity directly affects the degree of unstable failure of the joint.In the case of underground excavation,the heterogeneity of the discontinuities parameters affects the damage of each joint.The shear stress-time curve and shear displacement-time curve of each joint form a sharp contrast with the homogeneous discontinuities.The heterogeneity of the discontinuities directly affects the amount of energy released during unstable shear failure,and the amount of energy released of the discontinuities with different homogeneity coefficients is different.Considering the heterogeneity of the discontinuity,we can understand the more realistic shear behavior of natural discontinuity.Through the numerical simulation of the double-shear model under different sizes,the results of the negative size effect are obtained.By changing the size of the double shear test model,the result of negative size effect is obtained.The effects of elastic modulus and normal stress on the size effect are also simulated,and the size effect weakens as the elastic modulus and normal stress increase.Therefore,laboratory small-scale test results cannot be directly used in engineering.