Connected Pathways in the EDZ and the Potential for Flow Along Tunnels

Abstract

Two connected permeability experiments have been conducted at the Underground Research Laboratory. The tests allowed the examination of the hydraulic properties of the excavation damaged zone (EDZ). One test was conducted in a drill-and-blast excavation in a low stress environment, the second in a mechanically excavated tunnel in highly stressed rock. These two experiments allowed the comparison of flows through a blast-induced EDZ to flows through a stress-induced EDZ. In the drill-and-blast excavated tunnel, 98% of the flow was eliminated by forcing the fluid pathway to span adjacent blast rounds, suggesting a predominantly discontinuous EDZ. In the mechanically excavated tunnel, high stress concentrations created a very small continuous zone (0.05 m2) of highly fractured rock through which most of the flow occurred. Numerical modeling of a tunnel seal suggests that the construction of a well-designed EDZ cut-off will serve to minimize flows that would otherwise by-pass the tunnel seals.