A Spatial Numerical Approach for Heterogeneous Slope Stability Analysis in Open Pit Mines

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It is common practice in the preliminary stages of pit slope design to consider the engineering mechanical properties of rock masses, encountered at the mine site, as constant. The average parameter values obtained from sampling of each rock mass are considered to be characteristic of the mechanical properties of that rock unit. Deterministic conventional techniques used to characterize the engineering mechanical properties of rock masses take into account neither the spatial fluctuations of rock mass properties nor the uncertainty in the properties. This can result in over- or under-estimation of engineering rock mass properties and can have a significant impact on the results of any slope stability analysis. Under-estimation of engineering rock mass properties can result in the under-estimation of safety factors in pit slope design, entailing unnecessary stripping costs and imposing extra time and operational constraints. On the other hand, over-estimation of engineering rock mass properties can lead to the design of pit slopes with a higher risk of instability. This research project aims to develop new advanced modeling approaches that will allow incorporation of the spatial variability of rock mass properties into the pit slope design process. The main objective of this work is to advance the understanding of the influence of spatial variability and anisotropy of rock masses on the mechanics of rock slope failure. This methodology would allow the inherent heterogeneity of rock masses to be taken into account in open pit mine planning and design, on the understanding that more accurate knowledge of the spatial distribution of rock mass mechanical properties promotes safe and economic pit design. In the course of this research project, the geotechnical information (borehole database, ground mapping and core testing information) from two open pit mine sites will be used as known values of rock mass mechanical properties. The geological and geotechnical field information allows the boundaries and contacts of different geotechnical zones in the study area to be identified. In practice, each domain takes the form of a 3D solid model or envelope. This will be followed by division of the geotechnical domains into 3D blocks. A geostatistical simulation approach will be used to generate spatially variable properties of rock mass, based on the available sampling data. Several realizations of the spatial variability of the geomechanical properties will be created in the form of 3D block models. These block models together with discrete fracture network models will be used as inputs for generation of 3D continuum and brittle fracture numerical models for rock slope stability analysis. A Monte-Carlo simulation approach will be used for slope stability analyses of the stochastic numerical models. This allows to relate probability of slope failure to spatial variability of geomechanical properties and consequently better quantification of uncertainty and risk. These innovative spatial numerical models enable more effective assessment of pit slope design. Consequently, this will have a very positive impact on the economic and technical aspect of open pit mine planning and design.