Prediction of the pervious surround performance of blast damage zone to reduce groundwater flow in backfilled open-pits

ABSTRACT Reducing groundwater flow in backfilled open-pit to limit interactions of the backfilled wastes with the environment often relies on the creation of preferential flow paths around the disposed wastes in the form of a pervious surround. The blast damage zone, which consists of an enhanced permeability zone near the pit walls, could naturally contribute to creating such preferential flow, thus eliminating the need to build a permeable envelope, reducing costs and maximising the volume for wastes deposition. The objective of this research was thus to propose parameters that could easily be accessed on the field, so practitioners could predict the flow deviation and evaluate if the BDZ is a sufficient containment structure to reduce interactions between backfilled wastes and the environment. Results showed the BDZ deviation could be predicted using the BDZ size and pit wall permeability only, and within a precision of 15% without prior assumptions on the wastes or rock permeability. Three abacuses and one semi-analytical equation were proposed, and several criteria were derived to ensure the BDZ would act as a natural pervious surround. The results of these study should help mining operators and regulatory agencies to assess the BDZ effect on groundwater flow in backfilled open-pits.