Investigation on the mechanical behavior, permeability and failure modes of limestone rock under stress-seepage coupling

Limestone rock widely exists in various rock engineering, its mechanical behavior and perme-ability evolution have a great influence on the safety and stability of related engineering projects. To study the mechanical behavior, permeability and failure modes of limestone rock under stress-seepage coupling, triaxial compression coupled with permeability tests were carried out. Exper-imental results reveal that the failure of limestone still conforms to the Mohr-Coulomb criterion under stress-seepage coupling, and effective confining pressure 03eff can indicate the effect of gas pressure PG and confining pressure 03 on the deformation parameters of limestone samples. Peak stress 0P and residual stress 0R increase with the enhancement of confining pressure and decrease with the ascent of gas pressure. Permeability evolution of limestone under different gas pressures and confining pressures is generally similar, and the trend of initial permeability kI, peak permeability kP and residual permeability kR decreasing with effective confining pressure 03eff can be expressed by the exponential function. The increase of confining pressure and decrease of gas pressure will retard the acoustic emission (AE) response and inhibit the propagation of micro-cracks. More importantly, limestone samples always show composite failure modes dominated by tensile cracks under low confining pressure, while under high confining pressure, the limestone samples show shear failure modes. The difference is limestone samples are composed of tensile microcracks on the microscale under stress-seepage coupling, and the proportion of shear microcracks grows as gas pressure PG and confining pressure 03 increases. This research can provide a basic reference for relevant engineering applications.