Differential Mechanical Effects Of Sedimentary Bedding And Gneiss On The Tensile Deformation And Failure

The tensile failure mechanical behavior of anisotropic rocks is closely related to the anisotropy mechanism.Carrying out the differential research on the tensile deformation failure effect of different types of rocks is theoretical understanding of rock mass tensile failure is of great importance engineering and disaster prevention and control.In this paper,two typical rocks with sedimentary bedding and gneiss—sandstone and gneiss—were selected as the research objects,and Brazilian splitting tests were carried out at different dip angles.The tensile strength,strain field evolution,fracture surface roughness and failure mode of the two rocks at different dip angles were compared and analyzed.To explore the differential mechanical effects of sedimentary bedding and gneiss on rock tensile deformation and failure characteristics.(1)Both the tensile strength and the roughness of the fracture surface of the rock show obvious anisotropy characteristics.Among them,the anisotropy of tensile strength produced by sedimentary bedding is significantly stronger than that of gneiss.The average anisotropy coefficient of sandstone samples with sedimentary bedding is 3.33,which is significantly higher than that of gneiss samples(2.05).The roughness of the fracture surface of the two rocks decreases first and then increases with the increase of the loading angle,and the overall roughness of the fracture surface shows that the stronger the tension is,the higher the roughness of the fracture surface is.(2)Sedimentary bedding and gneiss can both affect fracture propagation behavior,but in different ways and degrees.The crack initiation points of bedding sandstone and gneiss in the Brazilian splitting test are distributed at the end of the sample,and the influence of sedimentary bedding on the failure process of sandstone after crack initiation is more than that of gneiss on the failure process of gneiss stronger.Under the same bedding dip angle,the failure crack deflection angle,the proportion of crack distribution along the bedding plane,and the loading angle range of shear failure of sandstone are larger than those of gneiss.(3)The difference between the cohesion of the matrix surface and the cohesion of the weak surface is the main reason for the differential mechanical behavior of sedimentary bedding rocks and gneissic rocks.The sedimentary bedding formed after deposition-compactionconsolidation has a large difference between the cohesion of the matrix surface and the cohesion of the weak surface,and the tensile cracks tend to expand along the weak surface during the expansion process.However,the difference between the cohesion of the matrix surface and the cohesion of the weak surface of the gneiss formed by high-temperature and high-pressure metamorphism is relatively small,and the expansion of tensile cracks is more disordered,showing the destructive characteristics of the coexistence of transgranular and surrounding grains.