Crack propagation and coalescence mechanism of double-hole cumulative blasting in coal seam
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摘要: 針對雙孔聚能爆破孔間煤層裂隙擴展貫通問題，基于對雙孔爆破應力波疊加效應的分析，建立雙孔聚能爆破數值分析模型，研究雙孔同時起爆時應力波的傳播特征、煤體的應力狀態、煤體裂隙擴展貫通規律以及應力波疊加效應對裂隙擴展的影響。結果表明，應力波疊加效應致使兩爆破孔中間截面上部分區域及其鄰域內形成均壓區，迫使部分徑向裂隙轉向，主導爆生裂隙空白帶的形成；兩爆破孔間的定向裂隙相互貫通后，爆生氣體相互作用促進貫通區裂隙的擴展并貫穿空白帶。同時，結合煤層深孔聚能爆破現場試驗發現，在兩爆破孔外側，應力波疊加效應促進裂隙的擴展，該作用隨著遠離爆破孔呈先增加后減小之勢；在兩爆破孔之間，應力波疊加效應抑制部分區域裂隙的擴展，致使兩爆破孔之間不同位置處煤層增透效果有起伏變化。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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圖 1 兩束應力波的正交（a）、斜交（b）干涉
Figure 1. Orthogonal (a) and oblique (b) interferences of the pressure waves
圖 3 煤層深孔聚能爆破數值分析模型
Figure 3. Numerical model of cumulative blasting with linear shaped charge in a coal seam
圖 4 煤層深孔聚能爆破雙孔同時起爆時應力波的傳播與干涉過程。（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
圖 5 煤層深孔聚能爆破模型中各個測點單元位置分布
Figure 5. Position distribution of each measuring point in the cumulative blasting model
圖 6 煤層深孔聚能爆破雙孔齊爆時各個測點單元應力（爆炸壓力）變化曲線
Figure 6. Pressure curve of each measuring point during the simultaneous detonation of two blastholes
圖 7 煤層深孔聚能爆破相鄰兩孔同時起爆后裂隙擴展貫通過程。（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
圖 9 煤層深孔聚能爆破相鄰兩孔同時起爆過程中應力波對兩爆破孔之間裂隙擴展的影響。（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
圖 10 煤層深孔聚能爆破相鄰兩孔同時起爆過程中應力波對兩爆破孔左側和右側的裂隙擴展影響。（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
圖 11 煤層深孔聚能爆破試驗鉆孔布置示意圖（單位：m）。（a）單孔爆破；（b）雙孔間隔5 m齊爆；（c）雙孔間隔9 m齊爆
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
圖 12 煤層深孔聚能爆破前后各個考察孔內瓦斯體積分數及純流量變化規律。（a～b）單孔爆破；（c～d）雙孔爆破；（e～f）單/雙孔對比
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
圖 13 煤層深孔聚能爆破后各個考察孔內瓦斯體積分數（a）及純流量（b）對比圖
Figure 13. Comparison of gas volume fraction (a) and gas pure flow (b) in each test hole
圖 14 煤層深孔聚能爆破后兩爆破孔之間各個考察孔內瓦斯體積分數（a）及純流量（b）對比圖
Figure 14. Comparison of gas volume fractions (a) and gas pure flow (b) in each observation hole between two blastholes
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