爆炸载荷下空孔及其缺陷对裂纹扩展影响机理研究

Effects of empty hole and its defects on the crack propagation under explosive loading

空孔在岩石爆破中的作用越来越受到重视,为研究岩石爆破中空孔及其缺陷对裂纹的影响,以PMMA代替岩石材料,利用动态焦散线系统重点研究空孔及其背爆侧缺陷对裂纹扩展的影响。在预制裂纹长度及其与炮孔间距不变的条件下,空孔直径为10 mm,20 mm和30 mm时,裂纹扩展长度分别为1.46 cm,2.13 cm和5.29 cm;裂纹扩展速度分别为266.64 m/s,366.63 m/s和466.64 m/s;应力强度因子分别为0.89,1.11和1.34;即随着空孔直径的增大,背爆侧预制裂纹扩展越容易。通过建立力学模型解释其机理,空孔直径加大了应力波的反射范围,增强了空孔边界处岩体单元的受力强度,导致裂纹的产生和发展。一定范围内空孔直径大小条件下,空孔反射应力波产生的合力方向对背爆侧裂纹扩展产生影响,主要表现为应力波的强度的水平分力方向与裂纹扩展方向的关系,当两者方向相同时对裂纹扩展起到促进作用,裂纹扩展越长;当两者方向相反时,起到抑制作用,裂纹扩展越短。

The role of empty hole in rock blasting is getting more and more attention.In order to study the influences of empty holes and their defects on the cracks propagation in rock blasting,PMMA was used to replace rock materials,and a dynamic caustics system was used to mainly study the influences of empty holes and their defects at the back-blast side on the cracks propagation.Under the conditions of the same pre-crack length and the same distance from the blasthole,when the hole diameter is 10 mm,20 mm and 30 mm,the crack length is 1.46 cm,2.13 cm and 5.29 cm,the crack propagation speed is 266.64 m/s,366.63 m/s and 466.64 m/s,and the stress intensity factor is 0.89,1.11 and 1.34,respectively,it is found by the experiments that as the diameter of the empty hole increases,the pre-crack propagation at the back-blast side is easier.The mechanism was explained by establishing a mechanical model.The increase of the diameter of the empty hole enlarges the reflection range of the stress wave,and enhances the intensity of the forces acting on the rock mass unit at the boundary of the empty hole,which leads to the generation and development of cracks.Under a certain range of hole diameters,the direction of the resultant force generated by the reflected stress wave of the empty hole affects the crack propagation at the back-blast side,which is mainly manifested in the relationship between the directions of the horizontal force component of reflective stress wave and the crack propagation.When the two directions are the same,the crack propagation is promoted propagated crack length is longer,when the two directions are opposite,the crack propagation is suppressed with shorter propagated crack length.