Study On Shear Mechanical Properties Of Rock Joints Under Cyclic Loading And Unloading

Taking rock joints as the research object,the shear characteristics of cyclic loading and unloading of irregular natural joints are studied by combining the indoor physical model test and numerical simulation.Based on the physical model test,the sensitivity analysis of the micro parameters is carried out.On this basis,using PFC2 D,considering the influence factors such as normal stress,joint occurrence,shear direction and so on,the numerical simulation supplementary research is carried out.The main results are as follows:(1)Through the indoor cyclic loading and unloading shear test,the influence of normal stress on the shear characteristics of jointed rock mass is obtained.The shear strength of joint face increases with the increase of normal stress in the shear process,and the shear stiffness decreases with the increase of shear displacement,and is strengthened and stable in three stages,when the joint shear is cut.When the shear stress is at the initial stage,the shear stiffness decreases with the increase of shear displacement.When the shear stress reaches the peak shear stress,when the shear displacement continues to increase,the shear stiffness is strengthened to a certain extent and then begins to stabilize.With the increasing of the shear displacement,the overall shear expansion angle increases first and then decreases.(2)Based on PFC2 D numerical simulation,the results show that the number of rock bridges has a certain effect on the peak shear stress of jointed rock mass,and the peak shear stress increases with the increase of the number of rock bridges and then decreases.The number of rock bridges has little effect on the deformation law in the pre-peak shear deformation zone of jointed rock mass.Although the shear stiffness is similar to that of the peak shear strength,the range of the whole variation process is relatively small.(3)With the increase of joint plane angle,the peak shear strength and stiffness of jointed rock mass show a nonlinear decreasing trend.When the joint plane increases to a certain angle,the peak shear strength decreases slowly and has a steady trend.For the same joint angle under the same normal stress level,the positive and negative shear direction has a great influence on the shear failure form of jointed rock mass,thus affecting the shear mechanical properties of the jointed rock mass.The shear strength and stiffness corresponding to the negative shear direction are larger.