Completion of tunnelling work on the 6.4km Lee Tunnel in east London, UK, has been recognised with a royal underground visit by HRH The Prince of Wales. The visit, on Wednesday (18 February), also marks the 150th anninversary of the city’s historic sewer network, which was opened in 1865 by the Prince’s great great grandfather, King Edward VII.
Prince Charles descended 75m below ground to inspect the 8.88m o.d. (lined to 7m i.d.) diameter CSO tunnel that runs between an 80m launch shaft at Beckton sewage works, through to the new Abbey Mills Pumping Station. Excavation of the main tunnel was completed by TBM in January 2014, following a drive that began in 2012. Thames Water says it expects to commission the new CSO tunnel and associated pumping infrastructure in December (2015).
The main tunnel, completed without intermediate shafts, is the deepest in London. A slurry Mixshield machine manufactured by Herrenknecht was selected to complete the drive under high groundwater pressures and through highly abrasive ground characterised by chalk and flint. More than 100 tonne of excavated chalk and water was removed as slurry for every one metre of tunnel advance. The last stage of constuction will finish at the end of this year when the final shaft has been excavated.
In addition to the 83m deep x 20m wide Beckton Overflow shaft, which also doubled as the launch shaft for the main TBM drive, three other deep shafts measuring 83m x 25m, 92m x 25m and 98m x 38m were excavated for the project. TBM works were completed by the MVB contractor joint venture of Morgan Sindall, Vinci Construction and Bachy Soletanche under a £422 million contract with Thames Water. A smaller diameter 750m connection tunnel was excavated separately using a 3m diameter TBM under a construction contract held by a joint venture of Laing O’Rourke and IMTECH.
The £635 million Lee Tunnel project is the first phase of the larger Thames Tideway Project. Final planning permission for the 25km-long Thames Tunnel, which will connect at its eastern extremity with the Lee Tunnel at Abbey Mills Pumping Station, was granted last year (2014). It is now in the construction procurement phase, and award of the first of three major tunnelling contracts, collectively valued at up to £2.25 billion, is expected later this year.