The Crossrail project in London included reusing the disused Connaught Tunnel. The 550m long tunnel runs below the Royal Docks, close to London City Airport. The tunnel was originally built in 1878. The planned refurbishment works proved challenging as the brick tunnel invert had to be replaced, further complicated by the fact that the crown of the portion running under the Victoria docks is very close to the dock bed. A solution was required to allow these delicate works to be undertaken to tight program constraints.
Working closely with our client, we developed a solution which allowed the staged replacement of the brick tunnel invert in greater lengths than was previously considered feasible. Our enhanced sequence allowed our client to enjoy significant program savings with reduced propping of the temporary excavation. Where the tunnel passes below the docks, cofferdams were used to facilitate the delicate refurbishment works. We independently checked the twin-walled cofferdams to ensure a robust design to allow the safe renewal of this historic tunnel.