Discrete Element Numerical Simulation Of Failure Mechanical Characteristics And Anchoring Mechanism Of Non-persistent Jointed Rock Mass

Most of the rock mass in nature has a large number of joints,faults and other defects,which make the rock mass have the characteristics of discontinuity and anisotropy,and easily lead to instability and failure of rock engineering.A large number of engineering practices show that the bolt has a significant supporting effect on jointed rock mass.Therefore,it is of great significance to study the deformation and failure characteristics of jointed rock mass and the anchorage crack arrest effect for the safety and stability of engineering.Due to the complexity of in-situ test and the failure evolution process of jointed rock mass specimens cannot be directly understood by laboratory test with current technical means,and numerical simulation tools can solve these problems better.In this paper,based on the discrete element PFC^3Dsoftware,the mechanical properties,failure characteristics and anchorage crack arrest effect of anchored jointed rock mass under uniaxial compression are studied,and the influence of confining pressure on the failure mode of joint specimen and bolt supporting effect is analyzed.The main conclusions are as follows:1.Using PFC^3D particle flow software and parallel bond model,the numerical model of non-persistent jointed rock mass sample is established.The method of removing particles is used to generate the pre cast joints,and the bolt is generated by re assigning new parameters to the particles in a specific area,and a complete numerical model of joint samples is obtained.The numerical simulation of the instantaneous uniaxial compression test of non-persistent jointed rock mass with bolt is carried out.The simulation results are compared with the indoor test results,and the feasibility of the numerical simulation experiment is verified.2.Under uniaxial compression test,the influence of joint angle and anchorage angle on the peak strength and elastic modulus of the specimen was analyzed.The evolution of microcracks in each group of specimens was analyzed.The limiting effect of bolts on the initiation and development of microcracks was studied.Then,the micro-crack characteristics of each group of samples are analyzed.The effects of joint angle and anchorage angle on the number of microcracks and the growth rate of micro-cracks at the peak strength are mainly studied,and the influence of bolt on the initiation stress of non-persistent joint rocksamples is analyzed.3.The conventional numerical simulation test of triaxial compression is carried out by PFC^3Dsoftware,and the stress-strain curves of joint samples under various working conditions are obtained by numerical simulation test.Through the analysis of the curve,we can get the variation law of the sample stress with the joint angle and the confining pressure strength.It is found that the trend of the stress-strain curve of the sample with bolt is basically the same as that of the sample without bolt,and they all contain the elastic stage,the yield stage and the failure stage.Furthermore,the strength parameters of rock samples with non-persistent joints are analyzed,including the variation of peak strength,the influence of confining pressure on elastic modulus and the influence of confining pressure and bolt on anisotropy.4.According to the triaxial compression numerical simulation test,the macro failure mode of the specimen is analyzed from the final failure mode diagram under each working condition,and the influence of different joint angle and confining pressure strength on the failure mode of the specimen is analyzed.Then,the micro-crack evolution process of the selected sample is used to analyze the micro mechanism,and the process of micro-crack initiation,propagation and through failure under triaxial compression is explained in detail.The crack initiation stress is calculated and compared with that under uniaxial compression.The influence of confining pressure and bolt on the crack initiation stress is analyzed.5.Based on the Jinping tunnel project,the numerical simulation of tunnel excavation and support is carried out by PFC^3D.The results show that for tunnel without support,the micro-cracks mainly gather around the tunnel,with a large degree of damage,obvious far-filed stress and large deformation of the tunnel;after the bolt support is used,the damage degree of the tunnel is effectively slowed down and the far-filed stress is large.The damage of surrounding rock mass is also restrained,and the deformation of tunnel is obviously restricted.