Blasting damage characteristics of surrounding rock around the arch foot of horseshoe tunnel
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摘要: 为解决隧道拱脚周边孔爆破难成形以致超挖和掌子面底部欠挖问题,研究了马蹄形隧道拱脚周边孔爆破围岩的损伤特征。依托方山隧道,建立了拱脚周边孔的三维数值模型,模拟了拱脚处围岩的损伤情况,分析了爆破效果与自由面形状、装药量以及空孔偏转角的映射关系,并通过现场试验进行了验证。结果表明:自由面形状显著影响围岩的损伤范围和炸药的能量利用率,相较于平直自由面,凹形自由面的损伤范围小,岩石的夹制作用更大,炸药爆破难以有效破碎围岩,能量利用率仅为78%;爆破效果随着装药量的增加呈先增大后减小的趋势,当拱脚周边孔的线装药密度为0.624 kg/m时,爆破效果最佳;此外,通过布设空孔和调整空孔偏转角,可以改善拱脚周边孔的爆破效果。采用优化后的爆破参数,拱脚处最大线性超挖量降低了53.1%,隧道轮廓成型平整。Abstract: To address the issues of over-excavation at the tunnel arch foot due to the difficulty of forming the perimeter hole blasting and under-excavation at the tunnel face bottom, the damage characteristics of surrounding rock caused by perimeter hole blasting at the arch foot of a horseshoe-shaped tunnel were studied through a combination of theoretical calculations and numerical simulations. On the theoretical level, an in-depth analysis of the stress distribution and crack radius in the arch foot area was conducted based on the principles of blasting mechanics, and the theoretical charge length for the perimeter holes at the arch foot was derived. Building on this, a 3D numerical model of the perimeter holes at the arch foot was established through numerical simulation. During the modeling process, the damage evolution in the surrounding rock during blasting was simulated by introducing an appropriate damage model, and post-blast damage cloud maps were generated. By comparing the damage cloud maps under different conditions, the relationship between blasting effectiveness and parameters such as free surface shape, charge amount, and void deflection angle was analyzed, further revealing the mechanisms by which these parameters influence the blasting formation results, which were validated through field experiments. The research results indicate that the shape of the free surface significantly impacts the extent of surrounding rock damage and the energy utilization efficiency of explosives. A concave free surface results in a smaller damage range compared to a flat free surface, with greater rock confinement, making it difficult for the explosives to effectively fracture the surrounding rock, leading to an energy utilization rate of only 78%. The blasting effectiveness shows a trend of first increasing and then decreasing with the increase in charge amount, with the optimal blasting effectiveness achieved when the linear charge density of the perimeter holes at the arch foot is 0.624. Additionally, by setting voids and adjusting the void deflection angle, the blasting effectiveness of the perimeter holes at the arch foot can be improved. With the optimized blasting parameters, the maximum linear over-excavation at the arch foot was reduced by 53.1%, resulting in a smooth tunnel contour. The research outcomes are engineeringly feasible and provide valuable insights for similar projects.
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表 1 隧道的爆破参数
Table 1. Tunnel blasting parameters
炮孔分类 段别/段 孔距/m 孔数 单孔装药量/kg 周边孔 11 0.6 30 0.60 拱脚周边孔 13 0.6 2 1.65 表 2 岩石的材料参数
Table 2. Material parameters of rock
密度/(kg·m−3) 初始裂隙度 压碎压力/MPa 压实压力/GPa 弹性剪切模量/GPa 静态抗压强度/GPa 拉压强度比 剪压强度比 2600 0 125 6 21.9 167.8 0.04 0.21 压缩屈服面
参数拉伸屈服面
参数参考压缩应
变率/s−1参考拉伸应
变率/s−1失效压缩应
变率/s−1失效拉伸应
变率/s−1压缩应变
指数拉伸应变
指数0.53 0.7 3×10−5 3×10−6 3×1025 3×1025 0.026 0.007 表 3 炸药的材料参数
Table 3. Material parameters of explosive
ρ/(kg·m−3) D/(m·s−1) A/GPa B/GPa R1 R2 ω E0/(MJ·m−3) 1200 3000 373 3.74 4.15 0.9 0.15 4.192 表 4 空气的材料参数
Table 4. Material parameters of air
C0 C1 C2 C3 C4 C5 C6 ρ/(kg·m−3) E0/(MJ·m−3) 0 0 0 0 0.4 0.4 0 1.29 2500 表 5 工况的设计参数
Table 5. Design parameters of working conditions
工况 孔深/m 装药量/kg 自由面形式 γ/(°) 1 2.4 1.5 平直自由面 2 2.4 1.5 凹形自由面 3 2.4 0.9 凹形自由面 4 2.4 1.2 凹形自由面 5 2.4 1.8 凹形自由面 6 2.4 1.5 凹形自由面 0 7 2.4 1.5 凹形自由面 15 8 2.4 1.5 凹形自由面 30 9 2.4 1.5 凹形自由面 45 -
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