ABSTRACT

Careful planning is required for a useful and comprehensive inspection of a rock tunnel. Tunnel inspections may be performed manually by visual observations made by walking through the tunnel or with the use of remotely operated vehicles (ROVs). Non-destructive testing and inspection technologies are commonly utilized for the inspection of lined tunnels including geo-radar and infrared thermal imaging. Unwatered inspections are ideally performed during no-flow conditions during a limited time period for a maintenance outage of operation. It is however also possible to perform an unwatered inspection during flowing conditions but this approach is associated with greater risks due to possible ROV power consumption when travelling against the flow. The purpose of unwatered inspections of hydraulic tunnels is to confirm the structural condition and overall acceptability for continued safe operations. A detailed risk assessment is performed as part of the planning for a tunnel inspection in order to fully recognize the possible hazards.