Experimental Study On Shear Mechanical Behavior And Acoustic Emission Characteristics Of Joint Surfaces In Rock-Like Materials

Shearing sliding along the joints is the main failure type of engineering rock mass.Acoustic emission technology can monitor the development of cracks and energy in the process of rock mass failure.Therefore,it is of certain engineering significance to study the mechanical behavior and acoustic emission characteristics of rock joints in laboratory.The artificial symmetric saw-tooth triangular joints made of cement mortar were specimens in this paper.YZW-30 rock straight shear apparatus and DS2 full information acoustic emission signal analyzer were used to carry out acoustic emission test during the direct shear process to study the influence of normal stress and asperity base angle on the mechanical behavior and acoustic emission characteristics of saw-tooth triangular joints.The main research results are as follows:(1)For saw-tooth triangular joints with small asperity base angles,the main failure type in direct shear tests is wear-out failure,while the cutting failure occurred for sawtooth triangular joints with large asperity base angles.Failure occurs only at the tooth tip of triangular joints under lower normal stresses.With the increase of normal stresses,the failure gradually expands to the entire triangular joints,the shear strength of joints increases gradually,and the dilation phenomenon gradually decreases in the shear process.With the increase of the asperity base angles,the shear strength of saw-tooth triangular joints gradually increases,the cohesion and friction angle of saw-tooth triangular joints also gradually increase.(2)The shear strength of saw-tooth triangular joints obtained in the test was fitted by Patton's bilinear shear strength model and Ladanyi's shear strength model respectively.Failure of saw-tooth triangular joints with small asperity base angles is mainly caused by friction between the upper and lower joints,which is more suitable for the bilinear shear strength model proposed by Patton.With the increase of the asperity base angles,the failure of saw-tooth triangular joints is related not only to the frictional effect between the joints,but also to the strength of the triangular sawtooth,so Ladanyi's shear strength model can reflects the cause of failure further.(3)During the direct shear test,there are little acoustic emission signal in most phases,and the obvious acoustic emission signal appears near the peak shear strength.Accumulated AE counts and energy show the same changing trend,and the curves can be divided into "quiet period","slow rise period" and "sharp rise period",which can be used to predict whether shear failure will happen for the jointed rock mass.With the increase of normal stresses,the peak time of the AE signal is delayed,the accumulative AE counts and accumulative AE energy are decreasing.With the increase of the asperity base angles,the slope of "sharp rise period" in the accumulative AE counts and accumulative AE energy curves is increasing,and the peak in accumulative AE counts and accumulative AE energy curves is also increasing.(4)PFC2D was used for numerical simulation,in which the direct shear test of sawtooth triangular joints is simulated to study the shearing mechanism and micro-cracks development.The numerical results showed that the results of numerical models are in good agreement with physical experiments and this numerical approach can reproduce the shear behavior of rock joints under different loading conditions.Numerical direct shear tests were carried out on asymmetrical joints under different normal stresses.With the increase of normal stresses,the shear strength gradually increases,the dilation phenomenon gradually decreases,and the number of cracks gradually increases.The relationship between shear strength and normal stress of asymmetrical joints is consistent with Braton's JRC-JCS shear strength model.