Fracture network analysis of the St-Eustache quarry, Quebec, Canada, for groundwater resources management

Abstract

A detailed structural survey has been conducted on a fractured sedimentary rock formation in the St-Eustache quarry, Quebec, Canada, to supplement a hydrogeological study. The two main types of discontinuities in the quarry are horizontal bedding planes and vertical joints. The fracture network is classified as a stratabound network that could be considered as an equivalent porous medium (EPM) for groundwater flow for a volume of rock of 25 to 100 m 3 . Using detailed statistical data of the fracture network, a geometric model is used to infer a range of hydraulic conductivity values for the low permeability fractures not directly measured with hydraulic tests and treated as EPM for their interpretation. This analysis shows that the vertical and horizontal fractures have about the same permeability in the rock mass, except for a few high hydraulic-conductivity bedding planes. Hydraulic conductivity of single fractures ranges between 1.7 × 10 −3 and 1.7 × 10 −1 m/s. The porosity of the bulk rock mass inferred from fracture spacing measurements was found to be between 0.03% and 0.3%. Because vertical boreholes provide limited information on vertical fractures, the interpretation of hydraulic tests at the site was greatly improved by the structural surveys.