Failure Characteristics and Scale in a Sandstone Joint Subjected to Direct Shear Testing: Experimental Investigation with Acoustic Emission Monitoring


 An in-depth recognition of the failure characteristics and scale of joints is of great significance for the stability assessment in rock engineering. Unfortunately, due to the close fitting of the upper and lower blocks of the joint under direct shear tests, the shear failure of joints are difficult to observe directly during the shear process. Thus, in this work, direct shear tests were carried out on sandstone joints subjected to three levels of normal stress while the acoustic emission (AE) in the rock is synchronously monitored. The failure characteristics of rock joints were then investigated by calibrating the AE system and combining them with the AE location results and shear load curves. A method was established to determine the failure scale of the rock joint that uses the AE moment tensor and first law of thermodynamics. The results show that the degree of failure of the rock joints increases as the normal stress increases. Also, the shear failure of the rock joints is localized and occurs synchronously, rather than sequentially in different areas. The average length of the microfractures formed in the shear process correlates with the average mineral grain size. On the other hand, the maximum length of the microfractures appears to have different values depending on the normal stress present. Our results have significant reference value for the precursory identification of shear disaster in engineering rock masses.