Research on the mechanical properties and energy evolution of pre-cracked sandstone samples

The current research on the strength and crack expansion law of single and multiple pre-cracked rock samples mainly focuses on small-scale pre-cracked rock samples. However, in actual engineering practice, the geological scale and occurrence of rock masses are larger, and the degree of fragmentation and the possibility of dynamic hazards after being affected by mining are greater than those of intact rock masses. In order to solve this problem, uniaxial compression tests on intact fine sandstone rock samples and pre-cracked large scale rock samples are carried out. Based on the analysis of the basic mechanical properties of intact rock samples and pre-cracked rock samples, the evolution mechanism of each energy index (total strain energy, elastic strain energy and dissipated strain energy) before the stress-strain peak of rock samples is obtained, and the influence of the pre-cracked inclination on the energy density during the whole process of deformation and damage of rock samples is revealed. The research results are showed as follows. ① With the increase of the inclination of the pre-cracked, the peak strength and peak strain of the rock sample decrease, and the rock sample changes from tensile splitting damage to shear slip damage. ② Corresponding to the elastic and plastic stages of the rock sample stress-strain, the pre-cracked rock sample has an accelerated energy storage period and a sharp energy consumption period. And as the pre-cracked inclination increases, the proportion of the dissipated strain energy and surplus strain energy of the rock sample increases. The increase indicates that the dynamic ejection damage ability of the rock sample is enhanced, the rock sample is broken, and the energy evolution of the intact rock sample is relatively gentle. Based on the results of the study, it is pointed out that in practical engineering, when exposing large scale and large inclination defects (faults, joints and other geological structures), it is necessary not only to prevent and control the fragmentation of the rock around the defects, but also to monitor the energy changes around the defects so as to reduce the hazard of structural impact of the rock mass.