A Study on the Drilling Methods to reduce Overbreak in Tunnel Blasting

터널발파 작업시 여굴 저감을 위한 천공방법 연구

  • 김양균 (코오롱건설㈜) ;
  • 김형철 (코오롱건설㈜) ;
  • 유정훈 (코오롱건설㈜)
  • Published : 2003.06.01


Overbreak or underbreak is one of the most important factors in evaluating the results of a tunnel blasting. Overbreak, which depends on the quality of rock, the type and quantity of explosives, and drilling conditions, has been a target of challenge to many blasting engineers because it directly affects construction cost. Drilling is generally known as one of the primary factors to generate overbreak. This study presents a real working model to reduce overbreak based on the analysis of drilling accuracy and overbreak generated from various working methods related to drilling. As the first step of the study, 45 experiments have been performed. The factors investigated are: marking contour line, the position of perimeter holes, the change of look-out with drilling rig position, and the proper space between perimeter holes. It is concluded that workers and engineers' will and efforts are the most important factors to reduce overbreak and that improving drilling method and pattern could reduce overbreak to a considerable amount.


Overbreak;Look-out;Perimeter Hole;Marking