Shaped energy blasting has been widely used in the field of geotechnical engineering because of its good orientation and high energy utilization. However, the bifurcation of cracks in the direction of energy accumulation seriously affects the precracking effect in the direction of energy accumulation. In order to study the influence of the shaped energy angle on the crack propagation and bifurcation in the direction of energy accumulation, this paper used theoretical analysis and numerical simulation to study the influence of the energy angle on the crack propagation law in the energy-concentration direction. It was found that the energy release rate in the direction of energy accumulation after blasting was the main determinant of crack propagation and bifurcation in the direction of energy accumulation, and it decreased with the increase of the shaped energy angle. When the energy release rate in the direction of energy absorption exceeded a certain critical value, the stress intensity factor K at the crack tip would be affected by the impact load more than the bifurcation toughness KB, resulting in bifurcation of the crack in the direction of the energy. The SPH method was used to simulate and analyze the energy blasting of four different shaped energy angles. The results show that as the shaped energy angle increases when the shaped energy angle is greater than or equal to 35°, the cracks in the direction of energy accumulation after blasting are bifurcated, two cracks at the crack tip. When the shaped energy angle is less than 24°, only one horizontal crack is generated in the direction of shaped energy, which is in good agreement with the theoretical analysis. The research in this paper will provide a certain research basis for the design of the blasting device and the optimization of the blasting effect.
The development of coal seam fissures and gas migration process caused by mining disturbance has an extremely important influence on gas control and roadway stability. In this study, the desorption, diffusion, and migration tests of adsorbed gas under the coupling effect of temperature and uniaxial compression were conducted on four coal samples from Zhangxiaolou mine, using the temperature and pressure coupling test system of deep coal rocks. The test confirms that the higher the temperature, the faster the desorption and emission of the adsorbed gases in the coal, and the larger the volume of the emitted gases. Meanwhile, it is found that the adsorbed gases in the coal samples of Zhangxiaolou mine are carbon dioxide and methane in the order of content. It is found that during the uniaxial compression process, several large negative values of the pressure of the emitted gas occur during the stable growth stage of the crack. This indicates that the crack expansion makes a new negative pressure space inside the coal sample, and the negative pressure values increase continuously during the unstable growth phase of the crack until the coal sample is destroyed. And after the axial pressure is removed, the escaped gas pressure shows a large positive value due to the rebound of the coal matrix and the continuous desorption of a large amount of adsorbed gas from the new crack location, which has a significant hysteresis with respect to the occurrence of the peak stress. Meanwhile, the SEM images of the coal samples before and after the test are analyzed to confirm the cause of the negative pressure generation.
In order to solve the rock burst disaster during the excavation of deep buried high stress hard rock tunnel, the method of changing the properties of surrounding rock by blasting is proposed in this paper. This method can effectively change the physical and mechanical properties of surrounding rock, reduce the storage capacity of surrounding rock corresponding to variable energy, and transfer the stress concentration position to the deep layer, which is an effective means to control rock burst. Taking the tunnel with rockburst tendency as an example, the stress distribution characteristics and displacement changes of surrounding rock under different modification depths are studied by using the numerical calculation method and elastic-plastic mechanics theory, and the effect is tested combined with microseismic data. The results show that the thickness of tunnel blasting loosening is closely related to the stress concentration of surrounding rock, and blasting loosening can effectively inhibit the occurrence and prevention of rock burst. With the increase of blasting depth, the maximum stress concentration decreases. The relevant research results can be used to reasonably design the blasting and loose surrounding rock reconstruction of high stress rock burst tunnel and improve the theoretical and practical basis.
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