1 EFFECT OF FRACTURE PERMEABILITY ON CONNECTIVITY OF FRACTURE NETWORKS

Many open pit mines are located in fractured rock systems where water flow paths are complex and difficult to predict. These flow paths are typically controlled by a small subset of fractures that are permeable and interconnected. Most models of flow in fractured rock systems are based on a network of interconnected fractures that are all assumed to be permeable. However this assumption is rarely observed in natural rocks where a significant fraction of the fractures within a connected cluster could be impermeable. Thus in studying fracture flow systems, we need to consider the permeability status (i.e. permeable or impermeable) of individual fractures in addition to the fracture network’s connectivity. Primary percolation clusters based on connectivity alone can be generated according to the fracture density, and probability density functions of fracture length and fracture orientation. These primary clusters, potentially including impermeable clusters, may not all conduct water. Hence percolation clusters need to be refined so that they comprise only open fractures. The density of these refined clusters can then be linked to the hydraulic conductivity, providing a more realistic representation of the natural system. Here we use numerical simulations to examine the effect (on connectivity and permeability) of removing a portion of fractures that are assumed to be impermeable. A discrete fracture network model is applied to formulate an analytical relation between two potentially measurable quantities of fractured rock systems, i.e., scan-line density of all fractures within core samples or boreholes and scan-line density of conductive fractures intercepted by boreholes. 1