A 100m long tunnel boring machine, which will be used to dig a four-mile sewer tunnel under east London, has been switched on for the first time during a handing-over ceremony in Germany.
This is the first and last time the machine will be seen in its entirety before it is taken apart to be reassembled 80 metres below London, where it will construct the Lee Tunnel.
The £635M tunnel, the UK’s deepest ever, will prevent 16M tonnes of sewage entering the River Lee each year – a result of London’s Victorian sewers not being big enough to cope with heavy rainfall.
A team of Thames Water tunnelling experts will rigorously inspect every aspect of the machine over the next two weeks at Germany’s Herrenknecht factory to ensure it is up to the major engineering challenge ahead, before it is transported over to the UK.
“The Lee Tunnel is the first of two tunnels, which will collectively capture an average of 39Mt a year of sewage from the 35 most polluting combined sewer overflows,” said Thames Water’s head of capital delivery Lawrence Gosden.
“We face the challenge of boring the deepest tunnel in London at some of the highest groundwater pressures that a machine of this type has tunnelled in. We will be passing through four miles of themost abrasive ground, without any other shafts along the way.
“The Lee Tunnel will tackle discharges from London’s largest overflow at Abbey Mills in Stratford, which accounts for 40 per cent of the total discharge. That’s why we’re dealing with this, the worst one, first.”
From mid-June, the tunnelling machine will be transported to London, where it will be reassembled in sections at Beckton sewage treatment works, before it is lowered into the ground. The machine will be transported by barge via Germany’s River Rhine to Rotterdam then shipped across the North Sea to Tilbury, on the Thames estuary in Essex, before being driven overnight in bits by lorry to Beckton.
The largest piece of the machine is the eight metre diameter cutter head, which will be transported in four parts. Even in pieces the equipment will be so wide Thames Water will need to temporarily move lamp posts and other obstacles on nearby streets to get it to site.
A ‘slurry closed faced’ tunnel boring machine is being used to tunnel the four-mile route beneath Newham. 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 on the Lee Tunnel is due to begin in January 2012 and is expected to finish in late 2013. The machine is likely to progress at a rate of 17m a day.
In addition to the Lee Tunnel and proposed Thames Tunnel, Thames Water is also upgrading London’s five major sewage works so they can treat more waste, preventing them becoming overloaded in rainfall, and improving the quality to which sewage is treated, to further improve river water quality.
MVB, made up of three civil engineering contractors - Morgan Sindall, Vinci Construction Grands Projets and Bachy Soletanche are working together to deliver the Lee Tunnel.