Deterioration mechanism of sandstone under coupling compression-shear stress and local borehole water pressure

This study focuses on the shear mechanical characteristics and crack propagation process under the influence of borehole water injection pressure. A self-developed rock shear-flow coupling experimental device was employed to investigate the progressive damage process and mechanical deterioration characteristics of a rock mass under local borehole water injection pressure. Acoustic emission (AE) technology analyzed the damage that occurred during the loading process, with particular emphasis on the AE rate, cumulative AE count, and b-value. In addition, the morphology of the fracture surface was reconstructed and analyzed using 3D scanning. The shear failure process under borehole water injection pressure can be classified into four main stages, with the most notable features being the variations in shear stress and AE rate. The experimental results indicated that the borehole water injection pressure significantly promoted the initiation and extension of tensile cracks and reduced the proportion of shear cracks. The effect of the water injection pressure is significant on the main fracture surface and is more pronounced in reducing the overall internal damage of the sandstone sample. Furthermore, we combined the Dugdale–Barenblatt model to calculate the main crack connectivity before shear fracture under borehole water injection pressure and achieved a quantitative evaluation of the weakening of the shear strength under local borehole water injection pressure.