Water saturation effects on the mechanical characteristics and fracture evolution of sandstone containing pre-existing flaws

Abstract

To comprehensively investigate the effect of water content on the crack propagation characteristics and fracture mechanism of jointed rock, uniaxial compression experiments were conducted on red sandstone specimens under different water content conditions and different bridge lengths. Acoustic emission (AE) techniques and digital image correlation (DIC) methods were applied to record the AE signals and deformation field of the specimens during the testing. The physical and mechanical properties, crack propagation characteristics and AE parameters of red sandstone under water–rock coupling were analysed. The results demonstrated that the water content and rock bridge length have conspicuous effects on the compressive strength, elastic modulus, temporal b value, P-wave velocity, and crack propagation model. The fracture initiates from the lowest pre-fabricated crack and the fracture mode gradually changes from shear to tensile fracture with the increase of the rock bridge length. Additionally, the micro-structure of the sandstone develops from a relatively dense pore cement structure to an irregular honeycomb structure. And the deterioration of the rock strength parameters could refer to the pore pressure generated by free water.