Experimental study on shear mechanical properties and damage evolution of artificial structural plane under constant normal stiffness

To study the influence of asperity angle and normal stiffness on the shear mechanical properties of the structural plane, a direct shear test of the artificial structural plane with constant normal stiffness (CNS) was carried out using the self-developed coal rock shear seepage coupling test system. The results show that the shear stress presents a periodic oscillation attenuation trend when the asperity angles are 15° and 30°. At the end of shearing, the reduction in peak shear stress with the increase of normal stiffness is 1.78, 1.42, 1.36 and 1.27 MPa, respectively, which is gradually decreasing. While the asperity angle is 45°, the shear stress gradually tends to residual strength after reaching the peak shear stress, and there is a one-to-one correspondence between normal displacement evolution and shear stress. With the increase of the asperity angles, the shear stiffness increases gradually. With the increase of normal stiffness, the peak shear stress of structural planes with 15° and 45° asperity angles increases linearly, and when the asperity angle is 30°, it presents the characteristic of piecewise function, but the peak shear dilatancy angle gradually decreases. The failure mode of the structural plane is obtained by analyzing the mass loss before and after shearing, the proportion of debris particle size, and the evolution of three-dimensional morphology parameters. When the fluctuation angles are 15° and 45°, the failure modes are relatively single, namely wear failure and tooth cutting failure. When the fluctuation angle is 30°, the failure mode has a strong and complex dependence on the experimental conditions, mainly including tooth tip shear failure and full tooth cutting failure. By combining the three-dimensional spatial point cloud data of the structural plane with the normal displacement values at the corresponding shear displacement, a simulated cloud map of the structural plane gap width at a specific shear displacement is obtained, which analyzes the dynamic evolution process of the structural plane during the shear process and obtains its failure mechanism. © 2023 China Coal Society. All rights reserved.