No abstract

A triaxial test under different confining pressures of the sandstone of Fuxin Hengda Coal Mine was carried out using MTS812.02 test machine to study the elastic energy–strain relationship and damage failure mechanism of deep rock. Then, the energy calculation method was used to calculate the elastic energy of sandstone under different confining pressure conditions. The elastic energy curve of rock under different conditions was drawn. The relationship between strain and elastic energies of rock was established on the basis of the relationship between elastic energy and energy release rate during rock loading. The relationship between strain and elastic energies was simplified by introducing stress state parameters on the basis of the generalized Hooke’s law. The micro-element strength was assumed to satisfy the Weibull distribution, and a new energy nonlinear evolution model was established by introducing the concept of rock micro-element strength. The method of determining the distribution parameters was also proposed. Results showed that the model and the experimental data agreed well with the experimental results. The model was close to the deformation and failure law of rock and could reflect the relationship between elastic energy and strain of rock. This relationship was aggravated by the cumulative effect of microcracks and cracks in the rock and was concentrated in weak areas. The damage evolution model of rock increased with the increase in strain and inclined to 1. The microcracks also penetrated into macroscopic cracks, and the rocks were unstable and destroyed.

Different stress creep tests are conducted on the sandstone in this study to better describe the creep properties of rocks under different stress states. A model that describes the rock creep process is established. The various stages of creep can be described by combining the creep properties of the creep elements of the model. A new method for determining creep parameters is proposed by using the special point on the creep curve and the definition of creep deformation. The relationship between the creep parameters, stress, and time is analyzed. An improved creep model that considers the effects of stress state and time on the creep parameters is developed. This model is verified using experimental data and calculation results. Results shows that the improved creep model better describes the creep properties of rocks and provides a new method for determining future model parameters. The shear modulus of elastic model controls the instantaneous deformation. The shear modulus of viscoelastic model governs the limit of viscoelastic deformation. The shear viscoelastic coefficient of viscoelastic model increases with the increase in stress. The coefficient of viscoplastic model controls the viscoplastic creep rate. The coefficient of a nonlinear Newtonian dashpot mainly controls the accelerated creep deformation of rock. The calculation results of the proposed model agree well with the experimental data under the action of different stress levels. This model accurately reflects the creep characteristics of the primary and steady-state creep stages, and overcomes the shortcomings of the traditional Nishihara model in describing accelerated creep.