Crack propagation and coalescence mechanism of double-hole cumulative blasting in coal seam
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摘要: 针对双孔聚能爆破孔间煤层裂隙扩展贯通问题，基于对双孔爆破应力波叠加效应的分析，建立双孔聚能爆破数值分析模型，研究双孔同时起爆时应力波的传播特征、煤体的应力状态、煤体裂隙扩展贯通规律以及应力波叠加效应对裂隙扩展的影响。结果表明，应力波叠加效应致使两爆破孔中间截面上部分区域及其邻域内形成均压区，迫使部分径向裂隙转向，主导爆生裂隙空白带的形成；两爆破孔间的定向裂隙相互贯通后，爆生气体相互作用促进贯通区裂隙的扩展并贯穿空白带。同时，结合煤层深孔聚能爆破现场试验发现，在两爆破孔外侧，应力波叠加效应促进裂隙的扩展，该作用随着远离爆破孔呈先增加后减小之势；在两爆破孔之间，应力波叠加效应抑制部分区域裂隙的扩展，致使两爆破孔之间不同位置处煤层增透效果有起伏变化。Abstract: This paper focuses on the radius of coal failure zones under cumulative blasting with shaped charge. Based on the analysis of the mutual superposition effect of the explosion stress waves during the simultaneous detonation of two blastholes, a numerical analysis model of the double-hole cumulative blasting with linear shaped charge was established. Additionally, the propagation characteristics of the stress wave during the simultaneous detonation of two blastholes, stress state of the coal body, mechanism of coal crack propagation and coalescence, and influence of the stress wave superposition effect on crack propagation were evaluated. Results show that the stress wave superposition effect induces the formation of a pressure equalization zone in the partial region of the middle section of the two blastholes and its adjacent regions. This occurrence forces the radial cracks of the two blastholes to turn, and they cannot connect with each other, leading to the formation of a gap blank zone between the two blastholes. After the directional cracks generated under cumulative blasting load coalesce, the collision of the explosive gases produced from the two blastholes further promotes the expansion of the cracks in the directional crack coalescence zone and eventually penetrates the gap blank zone. Field test results of deep-hole cumulative blasting in coal seams show that the explosion stress waves from the blastholes in the opposite side promotes the propagation of the blasting-induced crack on the left or right side of the two blastholes. This propagation first increases and then decreases as it moves away from the blasthole. Between the two blastholes, the stress wave superposition effect from the two blastholes inhibits the propagation of the cracks in some areas, resulting in a W-like fluctuation in the degree of improvement of the gas drainage effect at different positions in the area between the two blastholes.
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图 1 两束应力波的正交（a）、斜交（b）干涉
Figure 1. Orthogonal (a) and oblique (b) interferences of the pressure waves
图 3 煤层深孔聚能爆破数值分析模型
Figure 3. Numerical model of cumulative blasting with linear shaped charge in a coal seam
图 4 煤层深孔聚能爆破双孔同时起爆时应力波的传播与干涉过程。（a）t=1555 μs；（b）t=1710 μs；（c）t=1930 μs；（d）t=3250 μs
Figure 4. Stress wave propagation and interference process during the simultaneous detonation of two blastholes: (a) t=1555 μs; (b) t=1710 μs; (c) t=1930 μs; (d) t=3250 μs
图 5 煤层深孔聚能爆破模型中各个测点单元位置分布
Figure 5. Position distribution of each measuring point in the cumulative blasting model
图 6 煤层深孔聚能爆破双孔齐爆时各个测点单元应力（爆炸压力）变化曲线
Figure 6. Pressure curve of each measuring point during the simultaneous detonation of two blastholes
图 7 煤层深孔聚能爆破相邻两孔同时起爆后裂隙扩展贯通过程。（a）t=2500 μs；（b）t=2925 μs；（c）t=3085 μs；（d）t=6000 μs
Figure 7. Expansion and penetration process of coal seam fractures during the simultaneous detonation of two blastholes: (a) t = 2500 μs; (b) t = 2925 μs; (c) t = 3085 μs; (d) t = 6000 μs
图 9 煤层深孔聚能爆破相邻两孔同时起爆过程中应力波对两爆破孔之间裂隙扩展的影响。（a）t=1955 μs；（b）t=2320 μs；（c）t=2965 μs；（d）t=3085 μs；（e）t=4355 μs；（f）t=5630 μs
Figure 9. Effect of the stress wave on crack propagation between two blastholes during the simultaneous detonation of two blastholes: (a) t=1955 μs；(b) t=2320 μs；(c) t=2965 μs；(d) t=3085 μs；(e) t=4355 μs；(f) t=5630 μs
图 10 煤层深孔聚能爆破相邻两孔同时起爆过程中应力波对两爆破孔左侧和右侧的裂隙扩展影响。（a）t=3085 μs；（b）t=4355 μs；（c）t=5630 μs
Figure 10. Effect of the stress wave on crack propagation on the left and right side of two blastholes during the simultaneous detonation of two blastholes: (a) t=3085 μs; (b) t=4355 μs; (c) t=5630 μs
图 11 煤层深孔聚能爆破试验钻孔布置示意图（单位：m）。（a）单孔爆破；（b）双孔间隔5 m齐爆；（c）双孔间隔9 m齐爆
Figure 11. Trial borehole layout of deep-hole cumulative blasting (unit: m): (a) single-hole blasting; (b) simultaneous explosion of two blastholes at 5-m intervals; (c) simultaneous explosion of two blastholes at 9-m intervals
图 12 煤层深孔聚能爆破前后各个考察孔内瓦斯体积分数及纯流量变化规律。（a～b）单孔爆破；（c～d）双孔爆破；（e～f）单/双孔对比
Figure 12. Variations in gas volume fraction and gas pure flow in each test hole before and after cumulative blasting: (a−b) single-hole blasting; (c−d) double-hole blasting; (e−f) single-/double-hole blasting comparison
图 13 煤层深孔聚能爆破后各个考察孔内瓦斯体积分数（a）及纯流量（b）对比图
Figure 13. Comparison of gas volume fraction (a) and gas pure flow (b) in each test hole
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