Numerical Study On Crack Propagation Mechanism Of Rock Under Dynamic Loading

With the sustainable development of the domestic economy in recent years, the scale of the underground geotechnical engineering is more and more big and all kinds of complex rock mechanics problems are taken seriously. Instability and failure of many large engineering structure are closely related with dynamic loads, such as mining, tunnel blasting, et al. As rock is a heterogeneous material, when the stress is higher than the strength of rock, instantaneous energy release results in stress redistribution, which triggers dramatic deterioration of rock mechanical properties and rapid propagation of cracks. If don’t attach importance to it, serious engineering accident will occur and huge economic losses will be caused. Therefore, research on crack propagation mechanism of rock under dynamic loading is of important theoretical value and practical significance.Numerical code RFPA-dynamic is used to study the crack propagation mechanism of rock under dynamic loading in this paper, the main contents are as follows:1. By reading the relevant documents, the failure modes and crack extension of rock mass under dynamic loading are summarized in the aspects of theory, lab tests and numerical simulation.2. Two-dimensional numerical models of the rock explosion under in-situ stress condition were established. The process of crack initiation, propagation and coalescence of the rock mass under blasting load was simulated and the effect of explosive stress amplitude, stress ratio and confining pressure on the blasting cracks propagation are studied. The following conclusions were summarized:(1) When the stress ratio K increases from 0 to 0.75, the failure modes of rock mass is similar, two vertical main cracks are ultimately formed which are consistent with the direction of the maximum compressive stress, the length of the propagation cracks decreases and the damage of the rock becomes weak.(2) The explosive stress amplitude has a significant effect on the crack propagation, with explosive stress amplitude improves, the propagation capability grows.(3) When stress ratio K=1, four main cracks appear around the hole, and the initial stress field inside the rock changes when the confining pressure increases. The main failure mode turns from tensile-shear to shear and the length of propagation cracks decrease gradually. It illustrates that the confining pressure has an apparent inhibition to the propagation capability of blasting cracks.3. Numerical model was established to simulate the propagation process of single prefabricated crack in the rock specimens subjected to dynamic loading. Influences of the length and amplitude of stress wave, the inclination angle of pre-existing crack on the process of crack propagation are investigated. The difference crack propagation mechanics of rock subjected to dynamic loading and static loading are studied. The results show that:(1) When the length of stress wave is relatively short, new crack initiation is started from the top of pre-existing crack, and its direction and length are consistent with the pre-existing crack. When the length of stress wave continues to increase, the wing cracks are initiated from the ends of the pre-existing cracks and propagate perpendicularly to both ends of the rock specimen up and down. The failure pattern of rock specimen subjected to dynamic loading is similar to that under static loading when the length of stress wave increases to a certain degree.(2) The failure degree of the rock mass increases with the increase of the amplitude of stress wave.(3) Rock strength increases and rock mass is more difficult to damage with the increase of the inclination angle of pre-existing crack when it bears dynamic loading.(4) When the stress wave is very short, crack propagation mode is mainly controlled by the length of stress wave, the influence of the inclination angle of pre-existing crack is not obvious.(5) The failure modes of rock specimens subjected to dynamic loading and static loading vary greatly. Reflection tensile wave is generated in the parallel direction of joint surface and spallation phenomenon arise, but wing crack is more likely to arise when the rock is under the static condition.