To explore the anisotropy mechanism of joint shear strength from its damage characteristics

shear strength and failure characteristics were quantitatively analyzed. The study found that the shear strength and failure characteristics of joint show similar anisotropy with its morphology

and their anisotropy is weakened with the increase of normal stress. In addition

the influence of the inclination and height characteristics of the sawtooth joints on the shearing behavior was investigated. The analysis shows the angle and height characteristics of asperities have a positive correlation with shear strength

and the angle characteristics also determine the locality of asperities contact state during the shear process. The rough joint surface is composed of many microscopic asperities. The essential reason for the anisotropy of shear strength is the different contact area on the joint surface in different shear directions and the difference of asperities height and dip angle in the contact area. With the increase of normal stress

the failure of more and more micro convex bodies on the joint surface evolves from sliding wear to shear failure

and the difference of failure volume in different shear directions gradually decreases

which leads to the gradual consistency of the energy required for shear

which is the main reason why the anisotropic characteristics of shear strength are weakened by normal stress.