Structures, propagation characteristics of stress waves and dynamic fracture behavior in blasting

全面了解爆破过程中应力波和裂纹的动态行为，对于岩石开挖和混凝土结构局部拆除中断裂控制方法的发展是必要的。采用PMMA板、砂浆试件和电雷管进行了模型试验，研究了爆炸过程中应力波的结构、传播特性和动态断裂行为。应力波与切口圆孔的相互作用进行了检查和裂纹扩展沿着控制断裂面进行了观察。在这些实验中，应力波在爆破过程中的动态行为是通过应变测量。利用高速摄像机观察了裂纹沿着控制断裂面的扩展。获得了以下结果。（1）入射应力波到达装药孔附近20 ~ 110 mm处的6个应变片时，在PMMA试样中产生的径向压应变峰值从40000 ~ 5000μ应变衰减。传播速度从3000 m/s到2800 m/s不等，速度大于纵波速度。PMMA中的周向应变的峰值从大约6000 μ应变衰减到2000μ应变。高速摄像系统的图像显示，裂纹起源于装药孔以100 ~ 200 m/s的速度扩展。(2)在此基础上，进行了时间控制爆破的断裂面控制试验。装药孔产生的径向裂纹没有穿透控制断裂面，控制断裂面起着阻止这些径向裂纹的作用。(3)利用X射线计算机断层扫描（CT）系统对砂浆试件的裂纹结构进行了观察。X射线CT图像显示了炮孔附近产生的径向裂纹。

It is necessary to obtain a complete understanding of dynamic behavior of stress waves and cracks in the blasting process for the development of fracture control methods in rock excavation and partial demolition of concrete structures. In this study, model experiments were carried out to examine structures, propagation characteristics of stress waves and dynamic fracture behavior in blasting process using PMMA plates, mortar specimens and electric detonators. The interactions of stress waves with the notched circular hole were examined and crack propagation along the control fracture plane was observed. In these experiments, the dynamic behavior of stress waves in blasting processes was measured by means of strain measurements. The crack propagation along a control fracture plane was observed by means of a high-speed video camera. The following results were obtained.(1)Peak values of the radial compressive strain in the PMMA specimen produced by the incident stress wave arriving at six strain gauges placed between 20〜110mm near the charge hole decay from about 40000〜5000μ strains. The propagation velocity charges from about 3000m/s〜2800m/s and the velocity is larger than the P wave velocity. Peak values of the circumferential strain in PMMA decay from about 6000〜2000μ strains. The images of the high〜speed video camera system show that the crack originating from the charge hole propagates with the velocity of 100〜200m/s.(2) On the basis of these experimental results, the fracture plane control experiments using the time controlled blasting method were made. The radial cracks generated from the charge hole didn't penetrate the controlled fracture plane and the controlled fracture plane acts to arrest these radial crack.(3) The X-ray computed tomography (CT) system, which use the X-ray beam, was used to observe crack structure in mortar specimens. The radial cracks produced near the blast hole were shown by the X-ray CT images.