Experimental Study On Mechanical Properties And Failure Mechanism Of Layered Rock Mass

The layered rock mass is the most widely distributed type of rock mass in the most extensive construction and construction.It has important academic significance and engineering practical value to carry out research on its deformation and failure mechanism.In this paper,the strength and deformation and failure characteristics of layered rock mass are studied.The layered rock mass samples are made by gypsum.The indoor uniaxial compression test and direct shear test of layered rock mass are carried out.Based on the test results,the analysis of the corresponding results are carried out.The main work and achievements of the thesis are as follows:(1)The uniaxial compression tests of layered rock mass were carried out.The influence law of the lamination angle of the bedding plane on the uniaxial compressive strength and elastic modulus of the rock mass were studied.The lower layer of different laminar angles and the uniaxial compression failure morphology of the rock mass were analyzed.The results show that the mechanical properties and failure modes of the layered rock mass specimens are mainly affected by the dip angle of the bedding plane,but the influence of the spacing of the lamellar planes is small,and the uniaxial compressive strength increases with the dip angle of the bedding plane is firstly decreased and then increased,which is approximately "U-shaped" change law,and reaches the minimum value at about 60°.The variation of the elastic modulus with the inclination angle of the bedding plane is firstly reduced and then increased,but it is approximately "V-shaped",and reaches a minimum at about 45°.The deformation angle of the bedding plane is different,and the failure modes of the specimens are also different.The main failure mechanisms are tensile failure,shear slip failure,and combined failure of the two.(2)The direct shear tests of layered rock mass were carried out,the characteristics of the relationship between shear stress and tangential displacement of layered rock mass were analyzed,the influence of the dip angle on the shear strength of layered rock mass were studied,and the shear failure mechanism of layered rock mass was revealed.The results show that the relationship between shear stress and tangential displacement of layered rock mass can be divided into five stages: compaction,elastic deformation,microcrack development and macroscopic fracture formation,macroscopic fracture propagation and penetration stage,shear slip and displacement.The shear strength of the specimen is the lowest when the bedding angle is 0°,and the shear strength of the specimen is the highest when the lamination angle is 30°.The smaller the number of bedding in the sample,the better the integrity of the rock mass and the higher the peak shear strength.According to the shape of the specimen after shear failure,the failure mechanism is summarized as slip,shear and tensile fracture.The shear failure mechanism of the sample with a bedding angle of 60° was explained by a simplified theoretical calculation.(3)The direct and reverse direct shear tests of layered rock masses were carried out.The shear stress-tangential displacement relationship curves of the layered rock mass under forward shear and reverse shear and the similarities and differences of the normal displacement-tangential displacement relationship are compared and analyzed.The law of shear strength of layered rock mass samples under forward shear and reverse shear is studied.The deformation failure mechanism of layered rock mass under forward shear and reverse shear is revealed.In general,the shear stress-tangential displacement relationship curve,peak shear strength and residual shear strength,dilatancy(or shearing)of the layered rock mass with the same bedding angle during normal and reverse shearing The effects and destruction modes are different,and further research is worthwhile.(4)Through the in-depth interpretation of the theoretical basis of the Brazilian splitting method,combined with the relevant test results,the application range of the tensile strength of the rock mass measured by the Brazilian splitting method is studied,and the deficiencies of relevant norms and standards are pointed out.Recommended method for body tensile strength testing.