A New Blasting Method for Crack Control by Using Charge Holders

在岩石开挖和混凝土结构局部爆破拆除中，断裂控制是非常重要的。基于井筒中冲击波相互作用产生的动态效应，提出了一种利用两个楔形气腔的电荷保持器实现高度压裂控制的新方法。对装药座控制爆破裂缝的有效性进行了实验研究。装药座在井筒内产生冲击波汇聚效应，冲击波压力有效地作用于腔壁。在孔洞顶端位置的井壁上产生拉应力场，并产生受控裂缝。用电雷管作为药包，用PMMA板进行应力波的光学可视化，用砂浆试件和铅试件进行爆破效果的模型试验，得到了以下结果。激光照相术拍摄的照片显示，应力波从两个楔形空腔的尖端沿裂纹控制方向向外传播。装药座中的冲击波和气体的作用所引起的爆炸效应引发了裂缝，形成了一个控制破裂面。电荷保持器有效地消除了对井壁的损害，并将受控裂缝驱动到更远的距离。

Fracture control is very important in rock excavation and partial demolition of concrete structures with blasting. In this research, a new method for achieving high degree of fracture control by using charge holders with two wedge-shaped air cavities, based on the dynamic effects caused by the shock wave interactions in a borehole, are presented. The effectiveness of the charge holders for blast crack control is studied exprimentally. The charge holder produces shock converging effects in a borehole and the shock wave pressure acts effectively on the cavity walls. The tensile stress fields are produced on the borehole wall at the locations of the apexes of the cavities and controlled cracks are initiated. The following results were obtained from model experiments using a electric detonator as a charge, PMMA plate for optical visualizations of stress waves, mortar specimens and lead ones for examing blasting effcts. The photographs taken by the laser-shadowgraphy show that the stress waves propagate outward from the apexes of two wedge-shaped air cavities along the crack control directions. The blasting effects caused by the actions of the shock waves and gases in the charge holders initiate the cracks forming a control fracture plane. The charge holders are effective in eliminating the damage to the borehole wall and in driving the controlled cracks to greater distances.