The contract comprises a 32m-deep shaft, a 5m-long adit and a 2.5m ID, 220m-long pipejack. The drop shaft will convey the storm flows from the existing CSO down though a vortex generator and a drop tube to the connection tunnel.

The geological profile comprises 3m of made ground and alluvium, 6m of River Terrace Deposit and 44m layer of Clay, which is underlaid by the Lambeth group.

The primary lining of the tunnel will be 250mm thick precast concrete (the pipejack) and a 180mm secondary lining built in situ, for a finished ID of 2.2m. The shaft primary lining will be 325mm-thick SCL. The 400mm secondary lining will be casted in situ for a 6m finished diameter. Concrete reinforcement is by steel fibres.

Construction began in September and should take two years.

Barhale Contracts manager Ovi Frunza says: “Barhale is currently operating on all the three sections of the project and also the Thames Tunnel System Modification (TTSM) works at Beckton Sewage Treatment Works in East London that will support the overall Thames Tideway Tunnel project.”

The TTSM comprises a series of underground structures constructed at strategic points along the existing Thames Water network that amongst other functions it will enable flow from the exiting network to be intercepted by the new Tideway tunnel.