LONDON TIDEWAY TUNNELS LEE TUNNEL
AT THE HEAVIES AWARDS 2015, PROJECT OF THE YEAR WENT TO SARENS UK FOR THEIR USE OF COMBINED TECHNIQUES DURING THE CONSTRUCTION OF THE LEE TUNNEL, A VITAL PIECE OF THE LONDON TIDEWAY TUNNELS SCHEME. ANDY ADAMS SPOKE TO PROJECT MANAGER SIMON CRAWLEY TO FIND OUT JUST WHAT THEY ACHIEVED, AND HOW THEY MADE IT LOOK SO EASY.
Designed and built in the Victorian era, Sir Joseph Bazalgette’s brick sewer system has served the nation’s capital well, but is now completely out of capacity, serving a population of 8 million, which is twice that for which it was designed. The result is increasingly frequent discharges of raw sewage directly into the tidal section of the River Thames - 55 million tonnes of it last year alone - a situation which obviously cannot be allowed to continue. The Thames Tideway Tunnel will divert the current overflow and take it to Abbey Mills Pumping Station near Stratford, where the Lee Tunnel will take it on to Beckton Sewage Treatment Works to the east of the city to be processed.
The Lee Tunnel is both a transport and storage system, incorporating a series of vertical shafts along its length,which will serve as holding tanks for incoming sewage. These shafts flush downwards, creating suction, so horizontal props must be placed inside them to stop the walls from collapsing inwards. In the case of the main shaft, this meant 40 concrete props, each weighing 75 tonnes needed to be installed in a shaft 48 meters wide and 120 meters deep. As if that wasn’t enough, when Sarens UK were awarded the job by client MVB it was with a notice period of just 6 weeks!
“The client didn’t go for Sarens’ solution for cost, it was because it was innovative, self contained & safe,” says Crawley. “The other option was to use two cranes to tandem lift, which required the lift supervisor to continuously monitor the position and inclination of the props. This would be very difficult within a 120m deep shaft, having also to accurately co-ordinate the actions of the two crane operators to keep the props in a safe position. Our gantry solution only needed one operator, and no person needed to be near the props while the lift was in progress. Our client believed in Sarens ability to engineer and deliver this system.”