Shear failure characteristics of intermittent joints under constant normal stress

In order to deeply understand the shear failure mechanism of intermittent joints, shear tests and acoustic emission monitoring of intermittent joints with different joint angles are carried out. Based on the dominant frequency of acoustic emission signal, the quantitative analysis of fracture degree in the failure process is realized. By combining the shear failure strength, shear failure structures and the evolution process of fracture degree, the shear failure characteristics of intermittent joints are studied. The results show that the variation trend of SR1 at stage I of intermittent joints presents horizontal transverse S-shape, and SR2 presents symmetrical joint angle distribution. When the joint angle is positive small angle, SR1 is greater than SR2, while when the negative angle and positive large angle, SR2 is greater than SR1.The failure structures of intermittent joints can be divided into plane failure structure, zigzag failure structure and block failure structure, three failure structures are actually determined by four crack propagation modes. Joint angle controls the occurrence of large-scale failure, intermittent joints will have large-scale failure in stage I and stage II when subjected to large joint angle. However, the large-scale failure only occurs in stage I when the joint angle is small. The failure process of intermittent joints can be divided into four categories. With the increase of joint angle, the failure process develops from "unimodal abrupt" to "bimodal stable-stable", then to "bimodal abrupt-stable", and finally to "bimodal abrupt-abrupt".