Detection of leakage sensitive joint systems using resistivity measurements in connection with sub-sea tunnels

This paper presents an updated engineering geological interpretation of published resistivity profiles from the Maursund sub-sea tunnel in North Norway. It can be demonstrated that zones with low apparent resistivities are characterized by enhanced water leakage and a relatively high frequency of steep to vertical joints (e.g. joints/m 2 dipping 60-90°). Such joint systems are particularly sensitive to water seepage, and have recently been incorporated in an empirical equation for the estimation of water shielding requirements. The investigation has shown that pole-dipole measurements on the sea bottom reflect contrasting hydrological properties when the rock mass has a relatively low content of conductive minerals. RQD-, Q-values and seismic velocities do not generally reflect the variation in apparent resistivity. Hence, resistivity profiles provide information complimentary to seismic velocity data. Integrated interpretation may lead to improved accuracy in the total cost analysis of sub-sea tunnel projects.