水电坝基开挖中不同典型炮孔诱发振动的差异及其内因分析

明确水电坝基开挖中不同类型炮孔诱发振动的特性,对爆破振动安全控制具有重要的指导意义。通过现场试验比较了主爆孔、预裂孔和光爆孔三种典型炮孔诱发振动峰值(PPV)及振动主频(DF),并结合不同炮孔爆破作用边界条件的分析,借助数值模拟计算了不同爆破作用边界条件下岩石的动力响应特性,最后从爆炸能量分配与塑性区发展的角度,探讨了不同炮孔诱发振动差异的内因。研究结果表明:若单响药量与爆心距处于同一当量水平,预裂孔诱发的PPV及DF均相对大于主爆孔与光爆孔,而光爆孔诱发的PPV水平及DF与主爆孔大体相当;预裂孔一般先于主爆孔起爆,抵抗线较大,且多采用径向和轴向不耦合装药,由导爆索侧向引爆,其爆破损伤区和塑性区半径较小,消耗于岩石破碎的能量较少,转化为振动能的比例较大;光爆孔的装药结构及起爆方式与预裂孔相同,但其抵抗线较小,转化为振动能的比例及塑性区大小与主爆孔大体相当;爆破作用边界条件(装药结构、起爆方式及抵抗线等)的改变会导致爆炸能量分配及塑性区发展的不同,也是引起振动差异的内在因素。

Analysis of vibration differences induced by different typical blast-holes and the inherent causes in excavation of hydropower dam foundation

The study on the vibration characteristics induced by different kinds of blast-holes in hydropower dam foundation excavation is of significance for the safety control of blast vibration. Based on onsite blasting experiments, the Peak Particle Velocity (PPV) and the Dominant Frequency (DF) of blast vibration induced by the production blast-holes, the presplitting blast-holes and smooth blast-holes were compared in dam foundation excavation. Moreover, combining with the analysis of the blasting boundaries, the dynamic responses of rock mass were studied by using the numerical simulation software. Finally, the inherent causes of the differences of vibration induced by different kinds of blast-holes were discussed, from the views of the distribution of explosion energy and the development of plastic zone. The results indicate that when the maximum charge of each shot and the distance between the explosive center are at the same level, the PPV and the DF induced by presplitting blast-holes are relatively larger than those induced by production blast-holes and smooth blast-holes, while the PPV and DF induced by smooth blast-holes are approximate to the production blast-holes. The presplitting blast-holes are always the first fired blast-row. Their burden width is thus bigger than that of production blast-holes and smooth blast-holes. Moreover, the explosives charging in the presplitting blast-holes are generally radially and axially decoupled with the rock mass, so they are laterally initiated by the detonating cord. As a result, the blast-induced damage zone and the plastic zone is relative smaller. Therefore, less energy is consumed by rock fragmentation and more explosive energy is transmitted into vibration energy. The smooth blast-holes have the similar charging structure and initiation mode with presplitting blast-holes, but the burden width of smooth blast-holes is smaller. Consequently, the blast-induced plastic zone and transmitted vibration energy of smooth blast-holes are similar with that of production blast-holes. The blasting boundary (i.e., charging structure, initiation mode and burden size etc.) plays an important role on the distribution of plastic zone and explosion energy, which is the inherent cause of the differences of vibration characteristics.