地应力作用下偏心装药的炮孔裂隙分布

根据爆炸应力波和爆生气体的理论,考虑地应力的作用,结合断裂力学中最大周向应力理论,推导出了偏心不耦合装药条件下初始裂隙和扩展裂隙的计算公式。选取2号岩石乳化炸药和3类典型岩石参数对偏心不耦合装药下的裂隙范围进行了计算,并分析地应力对爆炸应力波引起的初始裂隙的影响。结果表明:炮孔壁上各点的不耦合系数由偏转角度α、炮孔与药卷半径之差决定;炮孔上不耦合系数的不同,致使偏心不耦合装药结构下裂隙分布十分不均匀,耦合侧与不耦合侧裂隙长度存在较大差异;地应力的存在抑制了裂隙的扩展,随着地应力的不断增大,炮孔周边裂隙范围逐渐减小,不耦合侧最短裂隙对应角度α逐渐增大,且其裂隙范围接近粉碎区半径。当3类岩石爆破施工中遇到高地应力时,采用三角形布孔,考虑不耦合侧裂隙很短或者不产在的情况,炮孔间距应控制在0.45~0.70 m之间。

Distribution of Blasthole Fracture in Eccentric Charge Under In-situ Stress

Drilling and blasting is widely used in mining and tunnel excavation as an economical and efficient method of excavation.Among them,smooth blasting is the most common.The theory of smooth blasting theory is based on the concentric uncoupled charge structure. In the actual smooth blasting,the charge structure will change due to the existence of its own gravity,forming eccentric uncoupled charge.The change of the charge structure has made the previous theory no longer applicable,and the earth stress is a problem that cannot be ignored as the depth of the excavation changes. Therefore,in the presence of in-situ stress,the fracture area formed by eccentric blasting is determined to provide a theoretical reference for blasting construction.Because of the eccentricity effect,the uncoupling coefficient of the blasthole is different after charging.According to the definition of the concentric uncoupling coefficient,the equivalent uncoupling coefficient of each point of the eccentric uncoupled blasthole is given. Then based on the theory of blast stress wave and explosive gas,considering the effect of earth stress and the initial damage of rock,combined with the theory of maximum circumferential stress in fracture mechanics,the calculation formula of initial crack and extended fracture under eccentric uncoupling charge was derived. The No. 2 rock emulsion explosives and three kinds of rocks were selected as examples to calculate the initial fracture range of the marble,shale and sandstone under the eccentric uncoupled charge,drawing with Origin software.By observing the difference between the coupled side and the uncoupled side,and exploring the influence of the ground stress on the initial crack caused by the explosion stress wave,we compared and analyzed the variation of the initial crack range under different ground stresses.The results show that the uncoupling coefficient on the wall of the blasthole is related to the difference between the deflection angle α,the blasthole and the radius of the lap.The equivalent uncoupling coefficient on the wall of the blasthole hole results in a very uneven distribution of the eccentric uncoupled charge structure,and there is a large difference between the length of the coupling side and the uncoupled side.With the increase of ground stress,the range of cracks around the blasthole is gradually decreasing,and the angle α of the shortest crack on the uncoupled side gradually increases,and its range gradually approaches the radius of the smashing zone.The presence of visible ground stress inhibits the expansion of the crack.The higher the ground stress,the smaller the crack range.When high geostress is encountered in the selected three types of rock blasting constructions,it is necessary to consider the fact that the cracks on the non-coupling side are short or non-existent.The blast holes are arranged in a triangle and the hole spacing is controlled between 0.45 and 0.70 m.