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Last reviewed: 25.11.2013 - 5.11pm
The Lee Tunnel is the first of two tunnels, which will collectively capture an average of 39 million tonnes of sewage a year from the 35 most polluting combined sewer overflows (CSOs), built by the Victorians as part of a sewerage network that still serves London 150 years on.
The £635m tunnel will tackle discharges from London’s largest CSO at Abbey Mills Pumping Station in Stratford, which accounts for 40 per cent of the total discharge.
The four-mile tunnel will run beneath the London Borough of Newham from Abbey Mills to Beckton.
It will help prevent more than 16 million tonnes of sewage mixed with rainwater overflowing into the River Lee each year, by capturing it and transferring it to Beckton Sewage Treatment Works, which is being expanded by 60 per cent to enable it to deal with the increased volumes.
We face the challenge of boring London’s deepest-ever tunnel. This will involve tunnelling through high groundwater pressures and passing through four miles of the most abrasive ground, without any other shafts along the way.
Construction work started in September 2010 to build the 80-metre-deep shaft at Beckton sewage works, where tunnelling work will start.
A 120-metre-long tunnel boring machine, named Busy Lizzie by a local primary school for good luck, will be used to construct the seven-metre-diameter tunnel - the width of three London buses.
In 2011, we lowered Busy Lizzie, our giant tunnelling machine, into position 80 metres below the capital and started tunnelling early in 2012.
The machine has been custom-built to suit the ground conditions, which are predominantly chalk with highly abrasive flint.
Busy Lizzie is a ‘slurry closed faced’ tunnel boring machine. It will blend over 100 tonnes of excavated chalk with water for every one metre of tunnel advance, forming a white slurry – a similar consistency to single cream, before transporting it through a pipe the length of the tunnel, so it can be processed above ground.
Tunnelling work is began in January 2012, progressing at a rate of 17 metres a day. Tunnelling is expected to finish in January 2014.