Mechanical behavior, mesoscopic properties and energy evolution of deeply buried marble during triaxial loading

A series of triaxial compression tests were conducted on deep-buried marble to reveal its deformation and failure characteristics along with the formation mechanism under high in-situ stress. The effects of confining pressure on the strength, deformation of marble samples were firstly analyzed. Then, the internal failure characteristics and energy evolution of the samples were comprehensively investigated based on the micro-CT scanning technology and energy balance theory. Results show that the strength and deformation at damage stress and peak stress points of marble samples increase with the increase of confining pressure. Micro-CT reconstructions reveal that the microcracks in the uniaxial compression sample are mainly tensile cracks and the failure exhibits obvious brittleness and splitting characteristics. The failure mode of triaxial compression samples gradually changes to shear failure with the increase of confining pressure. The number of cracks decreases first and then increases, and the damage is intensified around the main shear failure plane of samples under high confining pressure, resulting in a large number of conjugate secondary cracks. Further, with the increase of confining pressure, the strength increases linearly at energy hardening point, but increases nonlinearly at energy softening point. At the peak stress point, both total energy U _tp and dissipated energy U _dp increase in a concave function, while the elastic strain energy U _ep and the circumferential strain energy U _3p (negative direction) increase linearly. Besides, the damage evolution driven by energy can be roughly divided into hardening phase, energy storage phase, damage softening phase, and residual phase. These results can provide a useful reference for further understanding the failure mechanism of rock under high in-situ stress for disaster prevention.