Meitan xuebao (Apr 2024)
Damage and failure mechanism of pre-static loaded rock under cyclic impact
Abstract
To study the damage and failure mechanism of rocks under the coupling effect of high ground stress static load and cyclic impact disturbance generated by mining and excavation, the multi-strain rate dynamic static superposition rock mechanics test system was used to carry out the experiments with different pre-imposed static loads (0.45/0.65/0.85σc) superimposed cyclic impact and the same pre-imposed static load superimposed with cyclic impact loads of different frequencies (0.5/1.0/2.0 Hz). The experimental results indicate that the peak strength of rocks in the dynamic static superposition test is smaller than that in the static load test, and the maximum deformation is greater than that in the static load test, indicating that the dynamic static superposition load has a significant promoting effect on rock damage. The evolution of strength, deformation, and failure under dynamic and static superimposed loads are consistent, also, peak strength, fracture duration are linearly negatively correlated with pre-loading static, and logarithmically positively correlated with cyclic impact frequency. The maximum strain, fracture fractal dimension, and fragment fractal dimension are linearly positively correlated with pre-loading static, and logarithmically negatively correlated with cyclic impact frequency. Under different dynamic and static superpositions, the evolution trend of the fractal dimension of rock surface cracks and fragment sizes are basically consistent, and the former is larger than the latter, that shows the synchronicity of the development of rock surface and internal cracks, and rock surface cracks are more prone to generation and expansion. As the pre-loading static increases or the impact frequency decreases, the rock failure gradually intensifies, and the failure mode undergoes a transition from “inclined shear failure to vertical tensile failure to overall burst failure”. The burst failure position extends from bottom to overall. To quantify the damage mechanism of pre-loading static and cyclic impact, a dynamic static superimposed damage factor evolution model was established, which comprehensively considers static load damage, different peak, frequency, and number of cyclic impact damage, and strain rate strengthening effects. Further dynamic and static superposition experiments were conducted, and the error rates of rock peak strength obtained from theoretical calculations and experimental results were 0.5%, 1.8%, 0.6%, and 1.7%, respectively, the errors were relatively small. The theoretical calculation strength based on the superposition of dynamic and static damage factors is lower than the experimental strength. Preliminary analysis shows that this is due to the microscopic hysteresis of damage development under high-frequency cyclic impact. The actual cumulative damage generated by cyclic impact is less than single impact damage multiplied by cycle number. In the later stage, the microscopic testing can be carried out to explore the evolution law of rock microscopic damage under cyclic impact and further improve the theoretical model.
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