Lee Tunnel

The £635 million tunnel is expected to prevent 16 million 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 100 m boring machine will be reassembled under east London and used to dig the UK’s deepest tunnel ever.

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.

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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 by lorry to Beckton.

Thames Water’s Head of Capital Delivery Lawrence Gosden said “This machine is the best of its kind in the world.

“Tunnelling is a risky business, especially on a project of this scale, so it's essential we use the best available technology and ensure every last detail meets our unique requirements,” he said.

The largest piece of the machine is the 7 m 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 4-mile route beneath Newham. It will blend 1,000 tonnes of excavated chalk with water, 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.

“The Lee Tunnel is the first of two tunnels, which will collectively capture an average of 39 million tonnes a year of sewage from the 35 most polluting combined sewer overflows,” Mr Gosden said.

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 17 m a day.

River Thames Tunnel

Work to test ground conditions from previously unexplored depths beneath the River Thames – including clay formed 50 million years ago – will continue until the end of June 2011, to help Thames Tunnel engineers develop the best tunnelling route and strategy.

Two rigs are drilling boreholes along the stretch of the riverbed up to 70 m beneath the river to provide core samples, which will be tested to identify the various conditions the tunnelling machine is likely to encounter – which include chalk in the east, mixed gravel in the middle and clay in the west.

The Thames Tunnel is urgently required to help tackle the 39 million tonnes of sewage discharged into the River Thames each year, due to lack of capacity in the capital’s Victorian sewerage network.

Head of the London Tideway Tunnels Phil Stride said “We need to build up a thorough technical understanding of the potential constraints along the proposed route to help us refine our scheme ahead of the second phase of consultation due in Autumn 2011.

“Eighteen boreholes will be drilled by the two rigs, supplementing the samples from the 200 cores we've already taken over the past year. Lab tests will provide us with a detailed understanding of the ground conditions, such as the levels of flint in the chalk, which will inform the design of the tunnel and the four large tunnel boring machines we will need to construct the Thames Tunnel.”

Ground investigations have already been completed in locations including Hammersmith and Fulham, Lambeth, Nine Elms and Vauxhall. Ground samples obtained will be added to a national library of samples, which is held by the British Geological Survey, after construction.

The target date for the submission of the planning application is 2012. Initial construction of the Thames Tunnel is provisionally scheduled to start in 2013 with completion expected in 2020.