Pit Slope Optimization Based on Hydrogeologic Inputs

With the variability of commodity prices and the constant increase of mining costs, it has become increasingly important to optimize pit slopes of mines, taking into consideration the complexity and the uncertainties presented by ground conditions. The variables in slope stability, geology, rock mass strength, structural defects, inherent and induced stresses, rock weathering, alterations, and groundwater, are well known, as are their impacts  on  slope  performance.  Most  variables  cannot  be  changed  to  optimize  slopes. However, groundwater is one variable that can be managed during pit excavation, to reduce the effect of pore pressure on slope stability. Hydrogeologists and rock mechanics engineers combine their efforts in order to quantify, simulate, and control the effect of groundwater pressures on pit slope performance. Based on comprehensive field hydrogeological data collection and interactive numerical groundwater and geotechnical modeling, it is possible to evaluate the water pore pressure effect on the pit slope, to provide an efficient depressurization strategy to meet the geotechnical engineering targets, and thus to develop cost-effective mine plans. This  paper  discusses  how  proper  management  of  groundwater  conditions  can contribute to mine planning and operations, through pit slope optimization. We show a complete approach from collection of hydrogeological data in the early stages of a project to design of an appropriate depressurization plan, taking into account the rock mass conditions, the mining plan, and the time to achieve an optimal pit slope.