Change in hydraulic properties of rock mass due to tunnelling

Abstract

Presented and discussed are aspects of changes to the hydraulic properties of rock mass due to tunnelling, but in particularly the change due to the opening or making of new fractures and voids in the rock mass as a result of deformation or relaxation of the tunnel opening and hence an associated increase in the permeability of the rock mass surrounding the tunnel. This process principally occurs in tunnels were high stress fields persist effecting rapid and large scale deformation or relaxation (>100 mm) in the presence of (heavily) jointed rock mass and fault zones. Examples and observations from water and ground inflow events, associated with hydraulic property changes which have occurred during the mining of the Tapovan-Vishnugad Head Race Tunnel, India, are given and which have caused trapping of the Tunnel Boring Machine (TBM) resulting in time delays and cost increases.