Application of 3D Geotechnical Block Models in Design of Open Pit Mines-A Case Study at Mont-Wright Open Pit Mine

摘要

It is a common practice in pit slope design to consider the average parameter values obtained from sampling of each rock mass at the mine, to be characteristics of the mechanical properties of that rock unit. Deterministic conventional techniques used to characterize the mechanical properties of rock masses take into account neither the spatial fluctuations of rock mass properties nor the uncertainty in the properties. This could result in over- or underestimation of rock mass mechanical properties. Underestimation of rock mass properties could lead to the underestimation of safety factors in pit slope design, entailing unnecessary stripping costs and imposing extra time and operational constraints. While overestimation of rock mass properties can result in the design of pit slopes with a higher risk of instability.In this paper, a case study from Mont-Wright open pit mine in Quebec-Canada is used to present the applications of 3D block models of geomechanical properties in the pit design. A 3D geomechanical block model was developed at the Mont-Wright open pit mine using geotechnical borehole data and geostatistical interpolation techniques. The spatial variation of geomechanical attributes such as the Rock Quality Designation (RQD), and Rock Mass Rating (RMR), etc. was modelled. This paper aims to analyse the applicability of the 3D block model for quantifying the spatial variation of geomechanical properties within the pit. The results of statistical analyses performed on the 3D block model indicated that the model statistically follows the borehole data that were used to build the block model. In addition, the 3D geomechanical model performs well in recognizing the rock masses of medium quality. However, the model is poor in representing the rock masses with extreme qualities of very poor and very good. In other words, the 3D model overestimates the poor quality rock masses and underestimates the good quality rock masses. It is concluded that the block model needs to be updated using geostatistical simulation techniques that can outperform the limitations of interpolation through traditional estimation methods.