International Journal of Geomechanics

Large deformation is a kind of geological hazard in the construction of soft rock tunnels, which hinders construction, threatens workers’ safety, and raises project costs. Accurately obtaining the large deformation characteristics and patterns of tunnels is the prerequisite for taking targeted support measures. First, a viscoelastic–plastic model that can simulate both the short-term strain-softening effect and the long-term creep effect was proposed to investigate the large deformation features of soft rock tunnels. Then, a sophisticated model for creep parameter inversion was developed using the support vector machine, genetic algorithm, and particle swarm optimization. Finally, the deformation, stress, plastic zone, and internal forces in the lining of a large deformation tunnel were determined using the proposed constitutive model and the creep parameters obtained by inversion. As the creep displacement only makes up 14.4–23.2% of the total displacement, the results demonstrate that the elastic–plastic displacement is much more than the creep displacement. Notably, the connection between the top and middle benches has the most pronounced horizontal movement, accompanied by a significant strain-softening effect, which ultimately becomes the weak point in the support system. The excavation disturbs the surrounding rock, causing a high-stress zone and a low-stress zone, with the interface located around the junction of the elastic and plastic zones. The bending moment is positive at the wall waist and negative at the vault and arch waist. In addition, there is a progressive rise in the bending moment from negative to positive at the arch foot.

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.