de Graaf, WW & Etchells, SJ 2013, 'Blast induced damage mechanism on final walls and the blasting methods to minimise damage', in PM Dight (ed.), Slope Stability 2013: Proceedings of the 2013 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering
, Australian Centre for Geomechanics, Perth, pp. 1315-1326, https://doi.org/10.36487/ACG_rep/1308_93_deGraaf
At most open pit mines, profitability is affected appreciably by the final slope angles of the pit. Steep stable and safe pit walls can be formed by accurate final wall drilling and blasting techniques. The violence of the blasting process both leaves damaged surfaces that must be made safe, and breaking beyond the desired limit will increase mining costs. Much can be done to significantly reduce the damage, although the geological conditions and geometry of excavation ultimately limits success.
The aim is to make the transition from well fragmented rock to an undamaged slope or wall in as short a distance possible. The success of final wall blasting techniques depends on the aims being achieved despite the conflict of purpose that may exist in the mine’s production environment. Various drilling and blasting techniques are applied to minimise the impact from blasting that causes damage on the perimeter wall. These techniques have a common objective to minimise fracturing and loosening of the rock beyond the excavation line, and include line drilling, pre-splitting, buffer blasting and trim blasting.
In final wall blasting, the degree of confinement of the explosives energy adjacent to the slope plays a key role in the amount of wall damage produced. The energy of the explosives should be directed away from the final wall. Avoid the false notion that the explosives energy must always be minimised to limit blast damage to the walls. The challenge remains to apply explosives energy in ways that limit damage to the walls, but produce the required fragmentation of the ore to enable high productivity. Perimeter blasting is about techniques to limit damage to the walls, by creating split surfaces to define boundaries and terminate crack development, reducing energy against the back wall, and diverting it away from the perimeter zone.
de Graaf, W.W. (2010) Southern African Institute of Mining and Metallurgy, Drilling and Blasting School, Specialized blasting techniques, pp. 151–174.
International Society of Explosives Engineers (2011) ISEE Blasters Handbook 18th Edition, J. F. Stiehr (ed),
Laubscher, D.H. (1990) A Geomechanics Classification System for the Rating of Rock Masses in Mine Design, Journal of the South African Institute of Mining and Metallurgy, South African Institute for Mining and Metallurgy, Vol. 90(10), pp. 257–273.
St J Tose, S. (2006) A review of the design criteria and practical aspects of developing a successful pre-split, in Proceedings International Symposium on Stability of Rock Slopes in Open Pit Mining and Civil Engineering, 3–6 April 2006, Cape Town, South Africa, The South African Institute of Mining and Metallurgy, Johannesburg, pp. 525–546.