Experimental study on mechanical behavior, permeability, and damage characteristics of Jurassic sandstone under varying stress paths

Repeated mining of upper and lower coal seams causes roof sandstone to be repeatedly disturbed and results in the continuous deterioration of its permeability and damage properties, causing water leakage in the overlying aquifer, which significantly affects the surface environment and mine safety. This paper employed monotonous triaxial compression (MTC) tests and axial stress cycle loading and unloading (ACLU) tests to investigate the mechanical behavior of Jurassic sandstones. The acoustic emission (AE) data and permeability coefficient of the sandstones were simultaneously measured during mechanical testing. Results indicate that increased confining pressure enhances mechanical strength of the sandstones and reduces sandstone permeability, while increased permeation pressure reduces mechanical strength of the sandstones and enhances sandstone permeability under the MTC and the ACLU. The peak volumetric strain of the sandstones decreases and the volume expansion advances with decreasing confining pressure or increasing permeation pressure. The overall variation of permeability coefficient is closely related to the volumetric strain of the sandstones under the MTC and the ACLU. The AE characteristics exhibit a certain correspondence with different deformation stages and permeability variations of the sandstones under the MTC and the ACLU. In addition, the confining pressure and stress loading path can effectively change the damage evolution characteristic of the sandstones.