Developments of Fracture Plane Control Method and Fragmentation Control Method by High-Precise Time Control Blasting

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Fracture control in blasting is very important in underground excavation and demolition of concrete structures. It is required to produce a maximum of blasting effects with the use of a minimum of explosives. Therefore, it is valuable to obtain an understanding of the dynamic behavior of stress waves, gases and cracks in the blasting process for the development of fracture plane control methods. For the purposes, the model experiments were carried out by means of high-speed videography. A schlieren system using an Ar-ion laser as a light source was set up for visualization of stress waves and cracks in the blasting process. A high-speed video camera system was used to record visualization images in the dynamic fracture process. In this study, a guide hole method utilizing a circular hole with notches near a charge hole for achieving high degree of fracture plane control was presented. The effectiveness of the method was demonstrated by model experiments using PMMA and mortar specimens. … More In the experiment, the dynamic behavior of stress waves and cracks in blasting process was also observed by means of strain measurements and crack velocity measurements. The following conclusions are obtained.The model experiments using the schlieren system and the high-speed video camera system provide much useful information to understand the dynamic behavior of stress waves and cracks in a blasting process. Video images obtained from the experiments showed the propagation of stress waves and the dynamic behavior of cracks propagating along the control fracture plane. The guide hole method with notches is effective in controlling the orientation of the fracture plane and in driving the cracks along the control fracture plane to greater distances. This method can be applied to time controlled blasting for achieving fracture plane control and fragmentation control. It becomes evident from visualization images that the secondary crack is initiated by the interaction of stress waves with controlled fracture surface. Less