This study considers use of small-scale blasting as a breaching technique in rescue work. This paper focuses on the borehole angle in a reinforced concrete (RC) wall and its influence on fracture manners. In the experiments, the RC wall thickness was 250 mm and the blasting was conducted with a single-charge. Borehole angles were 90° and 45° to the surface of the wall. During breaching, two types of fracture manners were obtained with each borehole angle. While craters were observed on either side (borehole side or back side) at a borehole angle of 90°, craters were observed either on the borehole side or on both sides of the wall at a borehole angle of 45°. For rescue work, breaching needs to remove quickly the concrete of the wall as much as possible, while at the same time produce cracks on the other side without ejecting pulverized concrete. Fracture efficiency was defined to evaluate a fracture, irrespective of where the burden was located. In this study, a borehole angle of 45° resulted in high fracture efficiency in comparison to a borehole angle of 90°. Using the fracture manner in the borehole side at borehole angle of 45° and 90°, the relation between the amount of explosive and the burden required to provide the highest fracture efficiency was proposed, based on experimental results.
rescue work, borehole angle, fracture manner, burden, fracture efficiency