Analysis of mechanical properties and discing stress mechanism of deep marble in Jinping under true triaxial unloading conditions

The discing phenomenon is intimately associated with the condition of in-situ stresses, representing an indirect approach to ascertain original in-situ stresses due to its simplicity, operational ease, and economic efficiency. Moreover, the fracture morphology of discing in rock cores can partially elucidate the disturbance and fracture process. Based on deep marble samples from 2400 m depth at Jinping, this study executed rapid triaxial unloading mechanical experiments under varied operational conditions. It unveiled stress combinations conducive to discing and examined parameter selection for laboratory simulations of the phenomenon. Findings demonstrate that the strength and yield stress of marble samples notably enhance with the increase of the minimum principal stress during triaxial compression tests, paralleled by a gradual reduction in axial strain at the stress peak. In true triaxial unloading experiments, axial strain under equal biaxial confining pressures surpasses that under unequal biaxial confining pressures, which in turn exceeds that under uniaxial confining conditions, thus favoring the laboratory simulation of discing. The selection of axial stress during unloading at the sample’s elastic–plastic critical point, maintaining stress advantageous for augmenting axial strain post-unloading, offers theoretical insights into the discing phenomenon's mechanism.