Model experiment to study cumulative damage effects of young shotcrete under blasting load
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摘要: 利用模型实验的手段模拟了巷道的爆破掘进，并在实验中辅以声波测试，通过分析声波波速和声波波形的变化规律，研究了新喷射混凝土在多次爆破动载作用下的累积损伤效应。实验结果表明，爆破次数、与掌子面之间的距离和爆破药量均会影响喷射混凝土的累积损伤，这种影响体现在声波波速和波形2个方面：爆破次数增加、距离减小和药量增加，则声速降低值越大，波形变化越明显，即累积损伤值越大；爆破次数和距掌子面的距离均与累积损伤呈非线性关系，其中距离与爆破损伤之间的非线性关系可以用二次多项式进行较好的拟合；第一次爆破对声速和波形影响最大，造成的单次损伤值也最大；在小药量爆破的情况下，测试面的最大累积损伤值达到了0.1268，表明爆破近区喷射混凝土的损伤是需要关注的重点。Abstract: In this work we simulated the blasting excavation in a mine tunnel using a model test. Adopting the sound wave test method, we investigated the cumulative damage effects of young shotcrete under multiple blasting loads by analyzing variations of acoustic velocity and acoustic waveform during the model test. The results indicate that all the following factors, the times of blasting, the distance between the tunnel face and the test plane, and the dosage of the explosive used as are responsible for the cumulative damage of shotcrete. Their influences are shown both in the acoustic velocity and the acoustic waveform: the more times of blasting, the shorter distance, and the greater explosive dosage, then the greater the reduction value of the acoustic velocity and the more obvious the change of the acoustic waveform, and the greater the cumulative damage value. Specifically, there is a nonlinear relationship between the times of blasting and the cumulative damage. Between the distance and the cumulative damage there also exists a nonlinear relationship, which can be well fitted by a quadratic polynomial. Furthermore, it is found that the first time of blasting affects the acoustic velocity and the acoustic waveform the most, and causes the greatest damage. In general, when the explosive dosage is small, the maximum cumulative damage reaches 0.1268, which indicates that the shotcrete damage close to the blasting area should be the major concern.
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Key words:
- mechanics of explosion /
- cumulative damage /
- model test /
- young shotcrete /
- sound wave test /
- blasting load
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图 3 喷射混凝土爆破累积损伤曲线
Figure 3. Damage accumulation curves of shotcrete under blasting load
图 5 累积损伤随距离变化的拟合曲线
Figure 5. Fitted curves of damage accumulation varying with distance
表 1 Ⅲ类围岩及模型材料力学参数
Table 1. Mechanical parameters of type Ⅲ surrounding rock and model materials
介质 γ/(kN·m-3) E/GPa ν σp/MPa cL/(km·s-1) Ⅲ类围岩 24.50~26.54 6~20 0.25~0.30 20~60 3~4.5 模型材料 18.85~20.42 0.77~2.56 0.25~0.30 2.56~7.69 1.22~1.84 实测值 19.6 2.49 0.29 7.8 1.61 
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表 2 主要参数的相似比例系数
Table 2. Proportional coefficient of main parameters
序号 对应物理参量 相似准则 相似比 1 线尺寸(L) CL 6 2 质量密度(ρ) Cρ 1.3 3 加速度(a) Ca 1 4 弹性模量(E) CE=CLCρCa 7.8 5 单轴抗压强度(σ) Cσ=CE 7.8 6 炸药药量(q) Cq=CρCL3 280.8 7 炸药爆速(v) Cv=CE0.5Cρ-0.5 1 8 应力(σ) Cσ=CE 7.8 9 时间(t) Ct=CL0.5 2.45
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表 3 回归拟合系数
Table 3. Regressive fitted coefficient
爆破次数 A B1/mm-1 B2/mm-2 R2 1 0.0457 1.4×10-4 -3.6×10-7 0.9716 2 0.0537 1.5×10-4 -3.8×10-7 0.9210 3 0.0782 2.0×10-5 -1.8×10-7 0.9802 4 0.0801 4.1×10-5 -2.0×10-7 0.9836 5 0.1041 7.0×10-6 -1.8×10-7 0.9337 6 0.1327 -5.2×10-5 -1.1×10-7 0.9972
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