空孔对直眼掏槽参数及爆破效果的影响研究

为解决含空孔直眼掏槽中炮孔间距、炮孔与空孔距离的确定问题,首先,从爆生气体膨胀做功致裂岩体和空孔效应入手,推导了爆生裂纹的长度计算公式,确定了掏槽炮孔间距a和炮孔与空孔距离L的计算公式,得到了大空孔直眼掏槽空孔处片裂区长度公式,确立了应力集中作用下空孔迎爆侧径向裂纹产生的判据;然后,以灰岩(硬岩)和泥岩(软岩)对比分析了不同设计思想下的爆破参数和掏槽效果;最后,结合工程实践验证了理论分析的可靠性。结果表明:不同设计思想下,含空孔直眼掏槽的爆破破岩机理不同,以a为主时,相邻炮孔间裂纹的贯通是形成槽腔的关键,而以L为主且考虑空孔效应时,炮孔与空孔优先贯通形成槽腔。硬、软岩中应力波(动作用)与爆生气体(静作用)对爆生裂纹长度的贡献率约为4∶1和9∶1,空孔效应导致的软岩的片裂区大于硬岩的,爆破参数设计时应重点考虑;而空孔处产生径向裂纹的临界距离均小于炮孔爆生裂纹长度与空孔半径之和,因此不会产生径向裂纹,爆破参数设计时可不予考虑。以上结果说明,不同设计思想对槽腔掏槽爆破参数和槽腔爆破效果影响较大,基于爆生气体致裂的爆生裂纹长度计算模型可为爆破参数设计提供参考。

Theoretical study of the influence of empty-hole on both the blasting parameters and the blasting effect of straight-hole cutting

The paper is aimed to determine the distance between blast holes (a) and the distance between boreholes and the empty holes (L) in the straight-hole cutting with empty holes. Firstly, by considering the crack mainly being fractured during the quasi-static expansion of explosion gas and the effect of empty hole, the calculation formula of the crack length is derived; and then, the calculation formulas of the distance between boreholes and the distance between blast holes and the empty hole are determined. Moreover, the formula of the length of the crack zone around the empty hole in the straight-hole cutting with large empty holes is obtained, and the criterion of the radial crack at the blasting side of the empty hole is established based on the effect of stress concentration around empty hole. Secondly, by considering two different design ideas, the blasting parameters and cut blasting effect are compared and analyzed for the blasting in both limestone (hard rock) and mudstone (soft rock),while the reliability of the theoretical analysis is verified by engineering practice. The results show that the rock breaking mechanism of straight-hole cut blasting with empty hole is different under the two design ideas. Namely, if a is taken as the main factor, then the coalescence of cracks between adjacent boreholes is the key factor to the formation of the cavity, whilst if L is taken as the main factor, the bore holes and empty holes are preferentially penetrated to form the cavity based on the empty hole effect. In addition, the contributions of stress wave (dynamic action) and detonation gas (static action) to the crack length in both hard rock and soft rock are about 4∶1 and 9∶1, respectively. Considering the empty hole effect, the flake fracture zone in soft rock is larger than that in hard rock, to which more attention should be paid in the design of blasting parameters. Whereas, the critical length of radial crack initiated from the empty hole is less than the sum of the blasting crack length from cutting hole and the radius of empty hole, so that the radial cracks initiated from the empty hole will not be generated, which can be ignored in the blasting parameter design. The results indicate that the two different design ideas have great influence on cutting blasting parameters and blasting effect, and the calculation model of blasting crack length based on the driven of detonation gas can provide a good reference for the design of blasting parameters.