Study on evolution law of rock compression energy and nonlinear evolution model

In order to study the evolution law of compressive energy of rocks under different confining pressures, MTS815.02 testing machine was used to perform triaxial compression tests on Fuxin Hengda coal mine sandstone under different confining pressures, and the elastic energy change curves under different conditions were calculated by energy calculation method. The law of rock energy evolution under different confining pressures and the influence of elastic modulus on the variation of elastic energy under the same confining pressure were analyzed. Based on the generalized Hooke′s law and the law of conservation of energy and the relationship between elastic energy and energy release rate, a new energy nonlinear evolution model was established by introducing the concept of micro-element strength. The results showed that with the increase of confining pressure, the elastic energy and total energy of the rock showed a linear increase trend at the peak point and the energy in conventional triaxial compression was much larger than that of uniaxial compression. It showed that the confining pressure can effectively improve the bearing capacity of the rock. In the pre-peak stage, the model curve was fitted to the test data to a higher degree, and in the post-peak stage, the model curve could also better describe the relationship between elastic energy and axial strain. The overall model curve had a good fit with the test curve. This indicates that the model is closer to the actual deformation and failure evolution law of the surrounding rock, and the established model can better reflect the relationship between rock elastic energy-strain changes, and the parameters in the damage model could be determined through experiments. The introduced distribution parameters also has obvious physical meaning. Although the model curve and the post-peak test curve have large deviations, the model can not only describe the curve change law of the pre-peak stage, but also describe the change law of the post-peak curve, which makes up for the shortcomings of the original energy model that can not describe the curve of the post-peak curve.