Blast damage zone influence on groundwater fluxes through backfilled open pits

Abstract

The blast damage zone (BDZ) surrounding backfilled pits could significantly influence groundwater flow, increase flowrate through backfilled wastes, and potentially increase the dispersion of contaminants to the environment. A conceptual model of the fracture network of the BDZ was first proposed, which consisted of circular fracture oriented along the pit walls, and with a decreasing density with the distance to it. Realistic model parameters were also estimated based on the literature; BDZ equivalent permeability was analytically derived and used in 3D numerical models of conic open pits considering different backfilling scenarios. A total of 16 500 BDZ models were generated to assess the general influence of the BDZ on the flow and the influence of each parameter (fracture trace and attenuation length and fracture radius, aperture, and anisotropy). Results showed that the BDZ generally contributes to reduce (up to three orders of magnitude) the groundwater flow through backfilled tailings, but contributes to increase (by up to 250%) the flow in backfilled waste rocks, especially for wide and fractured BDZ in small pits. This study therefore suggests that the BDZ could be a self-sufficient containment structure to limit contaminant transports from backfilled tailings to the environment, but increases the risk considering waste rock.