Spathis, AT, Yuill, G & Stow, D 2009, 'Assessment of tunnel perimeters produced by blasting', in PM Dight (ed.), SRDM 2009: Proceedings of the First International Seminar on Safe and Rapid Development Mining, Australian Centre for Geomechanics, Perth, pp. 231-238, https://doi.org/10.36487/ACG_repo/902_22
(https://papers.acg.uwa.edu.au/p/902_22_Spathis/)
Abstract: Over break and under break are important measures of conformance to the designed perimeter in a civil or 
mine tunnel excavated by blasting. Three randomised paired trials of a new low-density bulk explosive 
compared with 70 g/m detonating cord loaded in the perimeter were made in different development headings 
of an underground zinc mine. The low-density bulk perimeter explosive produced more over break but less 
under break in two of the three comparisons with the detonating cord. However, a statistical analysis on the 
small number of paired comparisons indicated insufficient power in a paired t-test and further paired 
comparisons are recommended. Rather than the few well defined half-barrels of the detonating cord, 
characteristic scorch/crush zones were evident in the low-density bulk explosive rounds and miners observed 
somewhat increased barring down time in these blasts. Such observations are understandable due to the 
higher effective perimeter charge of the low-density bulk perimeter explosive. The maximum measured over 
break was less than 12% and the maximum measured under break was less than 8% for either blasting 
system. The miners stated that the speed of loading full faces was faster with the low-density bulk explosive 
system, compensating for longer barring-down times. Work is ongoing to improve the low-density bulk 
explosive as an alternative for mines seeking rapid development mining and tunnelling.