A settlement hazard risk management framework for the development of backfilled open-cut quarries

Surface mining operations typically lead to the disturbance of large areas of land over the life cycle of mines. With growing pressures on land use, particularly in urban areas, brownfield sites such as closed open-cut mines are being considered more and more for redevelopment opportunities. Naturally, these areas require reinstatement to some workable final surface level which is then suitable for the future development. Nevertheless, the business case that supports the decision to develop these complex areas should aim at balancing and optimising the investment required in the rehabilitation of the original site itself, as well as the cost of subsequent infra- and superstructure development. Controlled backfilling of these disused operations is often complex, including considerations of variability and engineering characteristics of the available backfill materials and the influence of groundwater recovery. Variations in the properties of the backfill material may not have any significant impact on some after-use activities (e.g. when the area is intended for conservation or agricultural land use after rehabilitation), but subsequent surface infrastructure development could be severely affected by settlement of backfilled land. The strategic planning and closure process for open-cut mines typically involves a number of different stages and a detailed consideration of the potential behaviour of the backfill is crucial in ensuring successful development. The purpose of this paper is to present a Risk Management Framework (RMF) focused on addressing excessive post-construction settlement. This RMF needs to form part of a more comprehensive geotechnical, and ultimately overall risk management and mine closure plan.