Energy Evolution Characteristics of Sandstone under Different High-Temperature Pretreatments and Different Confining Pressures

With the development of large-scale tunnel construction and green energy mining toward the depths of the Earth, the study of the mechanical properties and the deformation, and fracture characteristics of the surrounding rock mass under high confining pressures and high temperatures has become an urgent requirement. Therefore, we compare and study the effects of different high temperatures and confining pressures on the mechanical behavior and fracture characteristics of rock samples under loading and unloading conditions. In this paper, uniaxial and triaxial compression tests of sandstone at high temperature, and the stress–strain curves of red sandstone under different temperatures and confining pressures, are obtained. On this basis, the characteristics of energy conversion in the process of rock deformation and failure are studied. The research results indicate that the high-temperature effect weakens the brittle characteristics and enhances the plasticity of red sandstone, and there is a certain lag in the time of rock failure relative to the stress reaching peak strength. The high confining pressure weakens the brittleness and enhances the plastic properties of red sandstone, enhancing the overall resistance of the rock to deformation and enhancing its ability to store elastic deformation energy. According to the law of energy evolution, a new strength criterion is established to describe the three-dimensional spatial critical state surface of macrofailure caused by rock fracture coalescence. The study of the mechanical properties and failure criteria of rocks under high temperatures and pressures from the perspective of energy not only has important value for deep resource extraction but also has important theoretical significance for deep underground engineering construction.