Interlayer Shear Sliding Behaviors during the Fracture Process of Thick Sandstone Roof and Its Mechanism Leading to Coal Mine Tremors

To explore the causes of mine tremors in coal mines with sandstone roofs, a three-point bending loading experiment was designed for composite sandstone layers, and the fracture and interlayer shear slip characteristics of the composite sandstone layers were studied using optical measurement and acoustic emission techniques. The results show that the bending of the rock layers led to interlayer sliding deformation, while the fracturing greatly promoted interlayer sliding. The maximum interlayer slip accelerations during bending deformation and fracturing were 0.6 mm/s2 and 3.8 mm/s2, respectively. During the fracturing of the rock layers, the proportion of acoustic emission shear fracture events increased with the continuous occurrence of long-lasting and high-amplitude acoustic emission events. The mechanism of mine tremors in thick sandstone roofs is as follows: the increase in the area of the goaf causes rock bending deformation and fracturing, accompanied by interlayer shear slip, fracturing of the sandstone layer, and friction dislocation at the cementation surface of the adjacent sandstone layers, which jointly cause vibration of the roof.