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Excavation of first Lee Tunnel shaft completed

MVB — a joint venture of Morgan Sindall, Vinci Construction Grands Projets and Bachy Soletanche — has completed the excavation of the first of three shafts at Beckton for Thames Water’s 6.4km Lee Tunnel.

The 20m diameter, 75m deep Beckton overflow shaft was constructed by building 1.5m thick, 90m deep diaphragm walls and installing a 4.5m thick domed base slab. A slip formed liner will now be constructed in the shaft.

Diaphragm walls are also now complete for the Beckton pumping shaft and the Beckton connection shaft while excavation and finishing works are still to be done. Work is also now underway on the final deep shaft at Abbey Mills, which is the site for the start of the Lee Tunnel.

The £635M sewage storage tunnel will help prevent 16M.t of sewage entering the River Lee each year during heavy rainfall when the sewers become overwhelmed with stormwater, and untreated sewage is released to the river through combined sewer overflows (CSOs). The 7m diameter tunnel will capture discharges from London’s largest CSO at Abbey Mills Pumping Station in Stratford and transfer the flows to Beckton sewage works, which is being expanded by 60% to deal with the increased volumes. The tunnel will reach a depth of up to 75m and is due for completion in 2014.

The Lee Tunnel shafts

Diaphragm walls are complete on the three Beckton shafts, and work is continuing on the Abbey Mills shaft.

Fissure grouting has been completed for the tunnel boring machine (TBM) breakouts and for an 11m curtain below the overflow shaft’s diaphragm walls. Jet grouting will also be used at the Beckton Culvert.

The project also involves continuous flight auger (CFA) and rotary piling for the inlet bridge, tower cranes, power supply complex and culverts. The TBM, named Busy Lizzie by a local schoolboy, will be launched at Beckton at the start of next year.

 Internal diameterDepth below ground to structural slab levelD-wall depthD-wall thickness
Abbey Mills shaft25m68m83m1.2m
Beckton Connection shaft25m78.5m92m1.5m
Beckton Pumping shaft38m86.5m98m1.8m
Beckton Overflow shaft20m74.5m90m1.5m

 

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