Study on mechanical properties of fractured sandstone under stress-seepage coupling conditions

With the increase of mining depth of resources, the influence of high stress, high pore pressure and engineering disturbance on the mechanical behavior of rocks is more pronounced. This is particularly true in fractured rock formed under complex conditions, affecting the engineering safety. Focusing on fracture-developed aquifer sandstone commonly encountered in deep resource extraction, laboratory tests were conducted to simulate the stress process of fracture formation. Fractured sandstone specimens replicating the in-situ fracture-forming stress environment were prepared. Stress-seepage coupling tests were then performed on these specimens to investigate their deformation, strength, and permeability characteristics. The results show that both the deformation and strength of the fractured sandstone exhibit significant confining pressure strengthening effects and water pressure weakening effects. Under the low seepage pressure, the shear strength of fractured sandstone is determined by cohesion c and internal friction coefficient f, while with the increase of the seepage pressure, the shear strength is mainly determined by the internal friction coefficient f only. The permeability decreases with the increase of the confining pressure and increases exponentially with the increase of the seepage pressure. Considering the influence of confining pressure and seepage pressure, a prediction model of elastic modulus of the fractured sandstone is proposed under the conditions of σ₃≤16 MPa and P_w≤15 MPa.