Crack Propagation Law of Notch Blasting under Unidirectional Confining Pressure
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摘要: 深部煤矿爆破是初始地应力场与爆炸荷载共同作用的结果，采用单向动-静组合加载试验平台和动态焦散线试验系统，在有机玻璃板上施加与炮孔切槽平行或垂直的单向围压作用，探究了初始应力场强度对爆生裂纹的扩展规律。结果表明：炮孔切槽能够有效控制初始应力场的分布范围，促进能量集中释放，提高定向爆破效果，同时爆炸动载荷与围压静载荷分别在炮孔近区和远区占主导作用；水平初始应力场增强了切槽尖端应力集中程度，促进了主裂纹的扩展，且随着应力场增强，促进效果越明显，同时抑制了次裂纹的产生；竖直初始应力场降低了切槽尖端的应力集中程度，抑制了裂纹扩展，并使裂纹扩展模式由Ⅰ型转变为Ⅰ-Ⅱ复合型，且随着应力场的增强，剪切断裂越明显，且裂纹沿最大主应力方向扩展。Abstract: The deep coal mine blasting is the combined action of the initial ground stress field and the explosion load. By using the unidirectional dynamic and static combined loading test platform and the dynamic caustic experimental system, the expansion law of the initial stress field intensity on the blasting crack is explored under the horizontal or vertical unidirectional confining pressure applied to the blasthole notch on the plexiglass plate. The test results show that the grooving of the blasthole can effectively control the distribution range of the initial stress field, promote the concentrated release of energy, and improve the directional blasting effect. At the same time, the dynamic effect of explosion and the static effect of confining pressure are dominant in the near and far areas of the blasthole, respectively. The horizontal initial stress field increases the stress concentration at the crack tip and promotes the growth of the main crack. With the increase of the stress field, the promotion effect is more obvious, and the occurrence of secondary cracks is inhibited. In contrast, the vertical initial stress field reduces the stress concentration at the notch tip, inhibits the crack propagation, and transforms the crack from type Ⅰ fracture to type Ⅰ-Ⅱ mixed fracture. With the increase of stress field, the shear fracture is more obvious, and the crack propagates along the direction of the maximum principal stress.
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Key words:
- high ground stress /
- grooving blasting /
- dynamic caustics /
- crack propagation /
- high-speed camera
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图 7 试件破坏过程的动态焦散线系列图像
Figure 7. Dynamic caustic series diagram of specimen failure process
图 8 爆生主裂纹扩展速度随时间的变化
Figure 8. Variations of the growth rate of the main crack caused by explosion with time
图 9 爆生主裂纹动态应力强度因子随时间的变化
Figure 9. Variations of the dynamic stress intensity factor of the main crack caused by explosion with time
cp/(m·s−1) cs/(m·s−1) Ed/GPa $ \nu_{\mathrm{d}} $ c/(m2·N−1) 2320 1260 6.1 0.31 0.85×10−10 
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V/(L·kg−1) Q/(kJ·g−1) T/℃ D0/(m·s−1) 2320 5.9 4950 6600
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表 3 模型应力加载试验方案
Table 3. Model stress loading test scheme
Scheme Confining pressure design/MPa Actual loading/MPa $ {\sigma }{_{\rm H}} $ $ {\sigma }{_{\rm V}} $ $ \mathrm{\sigma}{_{\mathrm{H}}} ' $ $ \mathrm{\sigma}{_{\mathrm{V}}} ' $ M-1 0 0 0 0 M-2 1 0 3.3 0 M-3 2 0 6.6 0 M-4 0 1 0 3.3 M-5 0 2 0 6.6
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表 4 爆生主裂纹长度
Table 4. Blasting main crack length
Scheme Main crack No. Main crack length/mm Average length/mm M-1 A1 46.76 48.44 A2 50.11 M-2 B1 38.82 40.65 B2 42.47 M-3 C1 54.19 53.40 C2 52.61 M-4 D1 34.79 32.64 D2 30.49 M-5 E1 31.54 29.64 E2 27.74
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