1995 Fiscal Year Final Research Report Summary
A New Blasting Method for Crack Control by Using Charge Holders
| Project/Area Number |
04555153
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| Research Category |
Grant-in-Aid for Developmental Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
資源開発工学
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| Research Institution | Yatsushiro National College of Technology |
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Principal Investigator |
NAKAMURA Yuichi Yatsushiro National College of Technology Professor, 土木建築工学科, 教授 (00112392)
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| Co-Investigator(Kenkyū-buntansha) |
KUBOTA Satoshi Yatsushiro National College of Technology Associate Professor, 助教授 (00132671)
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| Project Period (FY) |
1992 – 1994
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| Keywords | Blast crack control / Charge holders / Stress waves / Shock wave interaction |
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| Research Abstract |
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.
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