| Engineering rock mass contains a large number of joints of different sizes,which control the strength and stability of engineering rock mass to a large extent.The strength of rock joints mainly refers to the shear strength,which is closely related to the shear direction.Based on the discrete element numerical test method,the forward and backward direct shear tests of rock joints with Barton standard profile features are carried out in this paper,and the shear mechanical properties of rock joints under forward and reverse shear conditions are obtained.On this basis,the shear strength criteria of rock joints considering shear direction are established.The main research results are as follows:(1)Aiming at ten Barton standard profile images,use Matlab image processing toolbox to conduct image pixel analysis,obtain pixel coordinates,average pixel coordinates to obtain two-dimensional coordinate data of discrete points of profile lines,and import them into Matlab program for reconstruction of standard profile lines.The profile reconstruction method is extended to the natural rock joint profile reconstruction,and the rationality of the new reconstruction method is verified by comparing the profile reconstruction and JRC value.(2)Based on ten Barton standard profile line discrete two-dimensional coordinate data and particle flow discrete element numerical simulation software,a numerical model of rock joints with Barton standard profile line topography is established.On this basis,the positive and negative shear numerical direct shear tests of rock joints under four normal stresses(1MPa,3MPa,5MPa and 7MPa)were carried out to obtain shear stress-shear displacement curves and normal displacement-shear displacement curves of rock joints under positive and negative shear conditions.On this basis,the influence of shear direction on the peak shear strength of rock joints was studied,namely: The peak shear strength under the forward shear condition is higher than that under the reverse shear condition(70%).The minimum and maximum difference of peak shear strength of rock joints with different joint plane types is4.11% and 25.18% under positive and negative shear conditions.(3)Based on the shear failure characteristics of rock joints in positive and negative numerical direct shear tests with Barton standard profile characteristics,the influence of shear direction on shear failure of rock joints is analyzed,that is,corresponding to the same rock joints,when the forward shear direction,the main failure location of joint plane is on the slope facing forward shear,and the failure situation is mainly nibbling failure.In the reverse shear direction,the main failure position of the joint plane is located on the slope facing the reverse shear,and the failure mode is mainly climbing and nibbling.(4)Based on the results of numerical direct shear simulation tests for rock joints with Barton standard profile features,a criterion for shear strength of rock joints considering the influence of shear direction was established,and verified by using the data of laboratory direct shear tests for rock joints reported in the literature.The results show that the maximum relative error between the theoretical predicted value and the experimental value of the shear strength criterion is 22.32%,which verifies its rationality. |
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