Case study: tunnels caves

Grizedale Reservoir, UK.

A major utilities company selected Benefil as the appropriate solution to infill a 50m service tunnel situated 20m below a reservoir embankment in Lancashire.

Conditions were challenging: the environmentally sensitive site had no access for HGVs or LGVs, work had to be carried out in a confined space, and there was a weight restriction on the embankment itself.

The Benefil team moved plant and materials to a pathway adjacent to the embankment via offroad vehicles and trailers. Supply hoses were then laid across a 70m traverse – including a 20m drop – to the fill point. Under confined space procedures, Benefil operatives installed delivery hoses within the tunnel, and a portable injection gun was placed at the entrance. Backfilling then commenced from the central spine of the Dam wall towards the operators situated at the downstream valve tower.

Only three days were necessary on site, and the entire filling procedure was observed in real time by infra red cameras within the void.