Rock breaking effect of plasma blasting under confining pressure
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摘要: 为向深部应力作用下爆破破岩工程提供新型破岩方法，开展了4组不同围压作用下的等离子体砂岩爆破实验，通过CT扫描和三维重构，对比分析岩石内部三维裂纹的形态结构和分布状况，研究等离子体爆破破岩技术在不同围压作用下破岩效果，并通过LS-DYNA进行数值模拟，建立了等离子体等效炸药模型，补充验证耦合应力场中等离子体爆破的作用规律，探究不同围压作用下等离子体爆破破岩机理以及岩体在爆破过程中内部裂纹扩展、分布及损伤演化规律。结果表明：相同电压作用下，随着三向围压的升高，岩石表面裂纹的数量和分布范围都呈逐渐减小的趋势，砂岩内部裂纹的复杂程度和贯通程度显著降低。由于在等离子体爆破产生的动态应力场和围压作用产生静态应力耦合场中，等离子体爆破产生的冲击波在爆炸初始阶段发挥主要作用效果，不同围压作用下岩石的裂纹形态和中心膨胀区域未出现明显差异，随着冲击波的衰减，三向围压在等离子体爆破过程的中后期发挥决定作用，抑制岩体的裂纹扩展和损伤演化。同时，随着围压升高，其对岩体内部裂纹扩展的抑制效果越显著，导致岩石内部三维裂纹的体分形维数和损伤度与围压作用均近似呈线性减小关系。Abstract: Plasma blasting rock breaking technology is characterized by green, high efficiency, controllability, and has a good application prospect in deep rock breaking. In order to provide a new rock-breaking method for the rock-breaking engineering under deep stress, four groups of plasma sandstone blasting tests under different peripheral pressures were carried out. The morphology, structure and distribution of three-dimensional cracks inside the rock were comparatively analyzed by CT scanning and three-dimensional reconstruction, so as to study the effects of the plasma rock-breaking technology in rock-breaking under different peripheral pressures. Meanwhile numerical simulation is conducted by using LS-DYNA, and a plasma equivalent explosive model in the coupled stress field is established to assist the verification of the coupled stress field, the plasma blasting mechanism as well as the rock-breaking process in the blasting process. Numerical simulation is conducted by using LS-DYNA to establish the plasma equivalent explosive model, supplementing the verification of the role of plasma blasting in the coupled stress field, and investigating the mechanism of plasma blasting under different pressures, as well as the rock body in the blasting process of the internal crack expansion, distribution and damage evolution laws. The results show that under the same voltage, with the increase of the 3D peripheral pressure, the number and distribution range of cracks on the surface of the rock exhibit a trend of gradual reduction, while the complexity of the cracks within the sandstone and the degree of penetration are significantly reduced. Due to the dynamic stress field generated by plasma blasting and the static stress coupling field generated by the surrounding pressure, the shock wave generated by the plasma blasting in the initial stage of the explosion plays a major role for the effect of different pressures under the action of the rock crack morphology and the center of the expansion of the region does not show obvious differences. With the attenuation of the shock wave, the 3D surrounding pressure in the middle and late stages of the plasma blasting process plays a decisive role in inhibiting the cracks of the rock mass expansion and damage evolution. At the same time, with the increase of the surrounding pressure, the more significant inhibition effect on the expansion of cracks in the rock body, resulting in the body fractal dimension and damage degree of 3D cracks in the rock body, while the role of the surrounding pressure approximately follows a linearly decreasing relationship.
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图 1 等离子体爆破破岩技术示意图
Figure 1. Schematic diagram of plasma blasting rock breaking technology
图 2 围压作用下等离子体爆破破岩实验装置图
Figure 2. Device diagram of plasma blasting rock breaking test under confining pressure
图 5 不同围压下砂岩试件上表面破裂结果
Figure 5. Surface fracture results of sandstone specimens under different confining pressures
图 8 爆后试件提取裂纹后的二值化图像
Figure 8. Binary image of post explosion specimen after extracting cracks
图 10 不同视角下内部裂纹分布图
Figure 10. Distribution of internal cracks from different perspectives
图 11 砂岩三维裂纹体的体分形数
Figure 11. Volume fractal number of three-dimensional sandstone fracture body
图 12 不同围压下试件体分形维数与损伤度
Figure 12. Fractal dimensions and damage degrees of specimens under different confining pressures
图 14 不同围压下测点有效应力随时间的变化
Figure 14. Effective stress variation curve of measuring points under different confining pressures
图 15 不同围压作用测点位移变化曲线
Figure 15. Displacement variation curves of t points under different confining pressures
图 16 不同围压作用下试件损伤演化云图
Figure 16. Cloud diagram of damage evolution of specimens under different confining pressures
表 1 爆后砂岩试件的上表面测量参数
Table 1. Upper surface measurement parameters of sandstone specimens after explosion
砂岩试件 施加围压/MPa 中心粉碎区面积/mm2 裂纹平均宽度/mm 最大裂纹长度/mm H-1 0 1193.99 3.90 53.40 H-2 2 778.92 2.30 49.40 H-3 4 514.46 1.30 46.00 H-4 6 349.49 0.60 43.00 
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表 2 裂纹特征参数表
Table 2. Table of fracture characteristic parameters
岩石试件 加载围压/
MPa裂纹表面积/
mm2裂纹密度/
mm−1裂纹有效
直径/mmH-1 0 28558.44 0.029 4.75 H-2 2 17146.92 0.017 4.20 H-3 4 12401.51 0.012 3.74 H-4 6 9503.69 0.010 3.39
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