Acoustic emission characteristics in tensile-shear failure of non-persistent jointed rocks with different undulation angles

Tensile-shear failure commonly occurs during the construction of deep in-situ tunnels. In this paper, direct tensile-shear tests were conducted on rock-like specimens containing regular serrated joints using a self-developed multifunctional rock mechanical test system. The influence of joint undulation angle variation on the tensile-shear strength, temperature, and acoustic emission (AE) was investigated. The results showed that the peak shear strength of the specimen decreased with the increase of joint undulation angle, and the increase of joint undulation angle led to the rock bridge being more prone to tensile failure and made the crack contour exhibit an obvious step-like feature. When approaching failure, the specimens all generated vigorous AE signals and yielded more cracks, which were accompanied by energy dissipation and manifested a decrease in temperature. During the loading process of the three specimens, the AE b values exhibited an overall trend of first increasing and then decreasing, with a dramatic fall near the peak strength. Cracks were classified by RA-AF values, and the results showed that in the initial loading process, the cracks were primarily of pure tensile types. The number of shear and composite cracks increased significantly when the specimens were close to failure.