Study on blast-induced fracturing for determination of optimal spacing between contour holes using PFC

In tunnel excavation, contour hole blasting is generally accomplished by smooth blasting to minimize the blast-induced stress and fracturing of rock beyond the excavation line. In order to successfully conduct smooth blasting, several factors have to be reasonably determined. They include types of explosives, spacing between contour holes and ratio of spacing to burden. Among these factors, choosing an appropriate spacing between contour holes according to the surrounding rock mass condition is essential in tunnel excavation. The objective of this work is to numerically investigate the optimal spacing between contour holes in five different rock mass class using Particle Flow Code. The extent of damage zone and propagation of fracture were monitored. Fracture information such as types, location, density, counts were tracked and analyzed. The optimal spacing between the contour holes was determined to be around 0.6 m in cases of rock mass class I & II and 0.7 m in cases of class III, IV and V