Evolution of Natural Joints' Mesoscopic Failure Modes under Shear Tests: Acoustic Emission Investigation

Abstract

Natural joints play an important role in the stability performance of rock engineering. To deeply understand the shear mechanism of natural joints (i.e., tensile fracture or shear fracture), direct shear experiments and acoustic emission (AE) monitoring were carried out for different kinds of joints under five levels of normal stress. By disposing the AE signals during a joint's shear process as AE samples databases, an optimal criterion to identify the tensile fracture and shear fracture modes was established based on the AE parameters, and this method was applied to reveal the shear damage of natural joints under the shear process. The results showed that the shear failure regions of natural joints were localized and inhomogeneous on a joint's surface, and the mesoscopic shear fracture and tensile fracture appeared along all the shearing process of the joint. The moment and the type of failure mode changed with the increase of the normal stress, but the main type of fracture did not change in each period during the whole shearing process, which provided a new way for disaster warning of shear damage.