Hydrogeological Decision Analysis: 3. Application to Design of a Ground‐Water Control System at an Open Pit Mine

Control of ground water plays an important part in operations at many open pit mines. Selection of an efficient and cost-effective ground-water control program is frequently complicated by the complex and somewhat uncertain hydrogeo-logic environment found at most mine sites. This paper documents a case study of dewatering operations at Highland Valley Copper that shows how risk-cost-benefit analysis can be used to identify the best ground-water control strategy to improve stability of pit walls under such conditions. For each of a specified set of design alternatives, the analysis involves evaluation of an economic objective function, comprised of revenues, operating costs, and monetary risks associated with slope failure. The risk calculation requires an accurate estimate of the probability of slope failure on the pit wall. The calculation involves a coupled, steady-state, saturated-unsaturated, finite-element ground-water flow model and a limit equilibrium slope stability model. The coupled model is invoked in a conditional Monte Carlo simulation that is based on a geostatistical description of the level of uncertainty inherent in the available hydrogeological and geotechnical data. Although the emphasis in this paper is on identifying the optimum slope angle and ground-water control strategy for open pit mines, the framework is equally well-suited to the analysis of design issues for any engineering projects in which the hydrogeological environment plays an important role.