Open Pit Mine Flooding Prognosis making use of Analytical Element Modelling in Fractured Hard Rock

A large number of South Africa's open pit mines are located in fractured rock. Analytical solutions to pit flooding mainly make use of the Dupuit- Forchheimer approximation. A typical example of such a solution is the solution proposed by Marinelli and Niccoli (2000). The challenge with most of these solutions is that the pit geometry is generally chosen as symmetrical and that the solution cannot accommodate geological structures. Numerical solutions to partial differential equations are available in the form of finite-difference, finite-volume and finite-element schemes. These solutions are able to solve for complex geometries and can accommodate geological structures, but require appropriate grid refinement to represent geological structures. The analytical element method (AEM) is a numerical method used to solve partial differential equations. It was initially developed by Strack (1989). The method does not rely upon discretization of volumes or areas in the modelled system; only internal and external boundaries are discretized. The AEM allows the open pit to be modelled as an asymmetrical element with thin and irregular inhomogeneities, which can be used to represent geological features. The AEM solution to pit flooding is more realistic than the typical analytical solution due to the relaxation of the pure analytical solution restrictions. This is especially true for scenarios where strip mining is simulated with continuous backfill taking place. Applying the AEM solution to open pit flooding scenarios is a quick and effective way to obtain first order flooding results. The advantage is that elements e.g. inhomogeneities that constitute the model, can be switched on or off since they are not dependent on a specific grid. This allows for quick changes to the model, by introducing new elements or removing elements to determine their influence on the result obtained.