Dynamic fracture process analysis of controlled blasts to minimize the excavation damage zone in underground excavations

Smooth surfaces with minimum damage in underground excavations have been demanded by the civil and mining industry such as the walls of tunnels and production drifts in underground mines. However, the consequences of aggressive blasting due to the lack of controlled blast design and precision drilling can lead to unexpected damage on the perimeter of the opening. The damages result in overbreak, loose rock to be scaled, and permanent damage to the remaining perimeters with the exposure of ground-fall hazards. To reduce injuries from ground falls, improved blast designs based on practical blast damage in perimeter blasting have been recommended by the National Institute for Occupational Safety and Health (NIOSH) through the DRIFT blast design software. This software models blast design using existing methods for perimeter blasting adding a new concept taken from the buffer row method with the perimeter row to reduce perimeter damage. In this study, to investigate the fracture process and pattern on the perimeter with a different application of the blast design method, the perimeter blasting was numerically analyzed using the two-dimensional dynamic fracture process analysis (2D-DFPA) with different perimeter drill-hole patterns. The influence of the blast design method and initiation error of the detonation on the fracture patterns are also discussed.