To investigate the effect of high temperature on the energy characteristics of marble, ANSYS/LS-DYNA was used to carry out dynamic compression simulation tests on marble with six temperature gradients at five impact velocities to analyze the mechanical properties of marble under high-temperature dynamic loading and the temperature effect on energy evolution, and to explore the energy criterion for strength failure of high-temperature marble from the perspective of energy dissipation. The results show that the Holmquist-Johnson-Cook (HJC) constitutive model can reasonably and effectively simulate the dynamic damage process of marble under different temperatures. With the increase in temperature, the dynamic peak strength and dynamic elastic modulus of marble exhibit a quadratic negative correlation with temperature, the dynamic peak strain exhibits a quadratic positive correlation with temperature, and the damage morphology is changed from X-type to conjugate shear damage. The increase in temperature reduces the energy storage capacity of the marble specimen to a certain extent, while the effect of high temperature on the energy dissipation capacity of marble is transformed from a facilitating effect to an inhibiting effect with 600 ℃ as the cut-off point. When the temperature reaches 600 ℃, the peak strength is significantly reduced, the ductility of the marble increases, crushing damage is presented, and the dissipated strain energy reaches the maximum value. 600 ℃ can be used as the threshold temperature for the brittle-delayed transformation of the marble. Based on the characteristics of the energy evolution process, the point of a steep increase in dissipated strain energy is regarded as a precursor information point of the precursor of overall instability and damage of marble. The inflection point at which the growth rate of the elastic energy consumption ratio first appears is defined according to the curve of the stress-elastic energy consumption ratio-strain relationship as the energy criterion of the strength failure of marble.

The fracture process of unloading confining pressure in deep-buried rock is related to crack propagation. The triaxial unloading tests under different initial confining pressures of 25,50 and 80 MPa were carried out on the MTS815 Flex Test GT Rock Mechanics Test Platform for the 2400 m deep-buried marble of Jinping II. The deformation and dilatation characteristics and energy conversion law in the process of unloading confining pressure were analyzed. Based on this, the crack evolution law in the deformation and failure process of deep-buried marble under different initial confining pressure conditions was explored. The research results indicate as follows: The deformation and failure process of deep-buried marble under unloading confining pressure has phase characteristics. The crack initiation stress and dilatancy damage stress were determined by the transverse strain difference method and the maximum point of volumetric strain. Based on this, the volume deformation process is divided into stages. And the volumetric deformation process is divided into two stages: stable dilatancy and accelerated dilatancy. The initial confining pressure has an effect on dilatancy of marble, with increase of initial confining pressure, the dilatancy property decreases but the ability to bear dilatancy increases. The propagation of cracks is accompanied by dissipation of energy. In order to clarify the dilatancy failure mechanism of deep buried marble under unloading confining pressure, the crack evolution law in the process of deformation and failure was obtained by integrating the characteristics of plastic strain and energy dissipation. It is found thatinitial confining pressure controls the type and development of cracks. With increase of initial confining pressure, the cracks develop more fully and the proportion of sliding cracks increases, and the failure mode changes from tensile shear failure to shear failure. The ransverse crack strain rate POC₃ was proposed to characterize the crack evolution trend in the unloading confining pressure stage. It is pointed out that the turning point of POC₃ curve corresponds to the extension of the main crack in the rock, and most of them are about 60% of the unloading value of the limit confining pressure. According to this, prediction of unloading confining pressure failure of deep buried rock can be conducted.