Study On Shear Characteristics Of Regular Dentate Joints

The existence of joints affects the safety and stability of rock engineering.Joints often undergo shear failure under external loading,so research about joint shear properties is essential,it is one of the hotspots of rock mechanics and engineering.A research method combining experimental and theoretical analysis was used to study the shear characteristics of regular dentate joints in this paper.Direct shear tests of joints under different undulating angles and different normal stresses were carried out,and the mechanical properties such as peak shear strength,residual shear strength and deformation of joints without “cavities”,joints with “cavities” and different “cavity” distribution forms were analyzed.It can be seen from the experimental results that the shear stress-displacement curve of the joint can be divided into four stages: the pre-peak linear elastic stage,the pre-peak nonlinear stage,the post-peak softening stage,and the post-peak residual stage.The shear stiffness in the pre-peak linear elastic stage and the pre-peak nonlinear stage before the peak,and the peak shear strength at failure of the joint are not only related to the undulating angle of the dentate protrusion and the normal stress on the joint,but also to the “cavity” distribution(locked patch distribution).The “cavity” distribution has little effect on the internal friction angle of the joint,but great effects on the performance of internal cohesive stress;the residual shear strength is only related to the normal stress on the joint,and not related to its initial morphological characteristics,which is in line with the law of friction.In order to explore the failure patterns and the shear strength of joints under shear loading,the stress state variation of regular dentate joint during direct shear was studied.The stress characteristics and stress states of a single dentate protrusion are analyzed,combined with the tensile stress and shear stress failure criteria,the location of failure surface and failure patterns of the dentate protrusion and the corresponding horizontal displacement when the dentate protrusion is broken under different normal stresses and geometric conditions.The shear strength prediction formulas corresponding to different failure patterns are obtained.Through parameter sensitivity analysis,the influence of different parameters(vertical stress ?,single dentate undulating angle i,friction coefficient ?,horizontal width of uphill slope l)on the failure mode and shear strength of single dentate are obtained respectively.Through comparison analysis,the theoretical prediction results in this paper are in good agreement with the experimental results.So the theoretical prediction results can provide certain theoretical support for analyzing the failure patterns and determining the shear strength of the joint.