Practical rock engineering in the optimization of stope dimensions — application and cost effectiveness

CIM Bulletin, Vol. 82, No. 926, 1989

J. W. Bawden, J. Nantel, and D. Sprott, Centre de Recherche Noranda, Pointe Claire, Quebec

The mine operator has two prime objectives when he operates a mine: (1) the mine must be safe, and (2) the mine must operate with the lowest possible costs. The operator constantly faces a dilemma; if he is over cautious with regard to safety, his costs may be very high, and if he is over-zealous in trying to reduce costs, the safety of his operation may be jeopardized. Modern bulk mining methods rely heavily on high productivity non-entry sloping techniques (e.g. open sloping, VCR, etc.). Such techniques have the advantage of removing the operator from the active and sometimes dangerous mining face and of minimizing costly development. On the other hand, this generally results in a certain loss of flexibility in following irregular ore—waste contacts. If slopes are opened too large and/or are inadequately supported, severe dilution with resulting escalating costs usually results. If initial access drift support is inadequate for latter mine induced stresses high rehabilitation costs may also be incurred. Optimization of stope dimensions should logically occur as part of a general mine rock engineering program, within the over-all mine planning context. The same program should help highlight those areas where drift rehabilitation may be a problem. Whenever successful mining is performed, rock engineering is being applied, either by design or by chance. The cost implications of planned practical rock engineering as an integral part of mine planning and design can be very significant to the ultimate mining "bottom line". At Noranda Minerals Inc. allowable stope dimensions are derived using a combination of numerical stress analysis and empirical design techniques. This paper discusses the use of the above techniques and their limitations as tools for rock mechanics based stope dimension optimization. The potential cost implications of such design efforts within the general mine planning context are also addressed.
Keywords: Rock mechanics, Cost effective mining, Empirical design techniques, Underground mining Mine design, Support systems, Safety.