In Scandinavia and worldwide, rock tunnels are largely used to transport water in many industries and municipal activities, e.g. hydro and nuclear power, water transport for drinking and wastewater, raw water supply to industrial facilities, etc. These tunnels are usually constantly filled with water but need monitoring and maintenance inspections at regular intervals.
According to the Swedish Energiforsk report (2021:730) "Inner waterways in a hydropower plant commonly have very limited access for inspections and some have never been inspected since the commissioning. Many plant owners lack systematic management of the inner waterways”. We do believe that this problem exists not only in Sweden and not only in hydropower plants.
Degradation of tunnel structure has many similarities in dry and water-filled tunnels; in the water-filled state, however, the hydrostatic pressure and its variation as well as physical erosion by flowing water are also added as possible negative factors.
Tunnel inspections must affect operations as little as possible. This can be achieved by performing inspection and maintenance with a ROV (Remotely operated vehicle) equipped with sonar, cameras and measuring instruments without emptying the tunnel of water and under safe working conditions. The combination of the correct size of the ROV and the length of the cable allows the inspection of tunnels of up to 20 km from a single-entry point.
We present the technical capacity of ROVs equipped with 3D sonar and examples of geological interpretation of inspection results from water-filled tunnels and maintenance solutions. We argue that a ROV equipped with 3D multibeam sonar is currently the most advanced instrument for performing inspections of water-filled tunnels in a safe work environment manner and should be considered as one of the tools for strategic management of inner waterways.
KEYWORDS
Hydropower; ROV; sonar; inspection; tunnel
