Linear Programming for Scheduling Waste Rock Dumping from Surface Mines

Abstract The removal of overlying waste rock in open pit mines to dumps is conventionally undertaken by draglines or by trucks and shovels, or by a combination of these. Waste rock dumps are the largest remnant structures of open cut mining operations and can absorb a large proportion of the mine operating costs. If the dumps are not properly developed they can be excessively expensive and can become a major safety risk and environmental hazard. There are many examples worldwide where poor design and construction of waste rock dumps have resulted in failures causing considerable loss of life and widespread damage, or have resulted in erosion and seepage that have led to severe environmental pollution. The proper design and scheduling of waste rock dumps and haul routes can significantly reduce costs, minimise the possibility of failures, and avoid harming the environment. This Thesis is limited to the consideration of trucks and shovels for waste rock haulage in open cut mining operations. It describes the development and application of a waste rock dump scheduling model using the Operations Research technique of Mixed-Integer Linear Programming, implemented in the mathematical modelling language AMPL. The model focuses on minimising the haulage cost for each block of waste rock taken from the open pit and placed in the dump. Allowance is made for the selective placement of benign and reactive waste rock, based on an open pit block model that delineates benign and reactive waste rock. The formulation requires input data including the xyz-coordinates of the block model for the open pit, information on whether the waste rock blocks are benign or reactive, the proposed time scheduling of waste rock haulage from the open pit, unit haulage costs, and the geometry of the waste rock dump, including the delineation of the zones that are benign and those that are reactive. The model was successfully tested by using both simple test data and actual mine site data. The application of the model to a simple case confirmed that it produces results that meet the Objective Function in producing an optimal haulage time and cost, and meets the various Constraints imposed. This model for scheduling the removal of waste rock from open cut mining operations with trucks and shovels will require further research and testing and, because the results are generated in a numerical format, there will also be a need to convert them to a graphical format to facilitate their interpretation. Ultimately, it will have the potential to provide a relatively low-cost scheduling tool that meets operators’ economic, safety and environmental goals