A study of smooth wall blasting fracture mechanisms using the Timing Sequence Control Method

Abstract

High quality of cracking and low depth of damage in sidewall is usually required in a blasting excavation. On the contrary, large spacing of blast holes can efficiently reduce cost. Therefore Timing Sequence Control (TSC) Method can be applied, so as to meet the challenge. In the TSC method, there is a very short delay between two adjacent blast holes, i.e., the Primary borehole (PBH) and the Target borehole (TBH), in sequence. Study of the cracking process around adjacent borehole indicates, larger stress concentration on the hole wall, if the TBH initiates after the stress wave from PBH has past it. The initial crack generated on the TBH is most likely to occur along the direction of borehole attachment.Our study also shows that, keeping the borehole spacing and borehole diameter as constant, a through crack can be formed between the adjacent boreholes when the delay time, spacing of PBH and TBH, and transverse wave velocity obey a certain relationship. Keeping the hole spacing between PBH and TBH, borehole diameter and the delay time for PBH and TBH as constant, borehole through cracks between the adjacent boreholes can be formed only when the spacing of TBH equal or below 25 times of borehole diameter.