Work to test ground conditions from previously unexplored depths beneath the River Thames will continue until the end of June, to inform the Thames Tunnel’s tunnelling route and strategy.
Two rigs are drilling boreholes along the stretch of the riverbed up to 70m beneath the river to provide core samples, which will be tested to identify the various conditions the TBM is likely to encounter.
Head of 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.
“18 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.
“To minimise the duration of works, the rigs will operate 24 hours a day, seven days a week in most locations for about one week. Where we cannot work continuously, it may take up to three weeks.
Work is scheduled to take place in the following locations:
- Barn Elms and Blackfriars Bridge (south side) – from 17 May
- Tower Bridge (south side) and Hammersmith Bridge (south side) – week commencing 23 May
- Wapping (near King Edward Memorial Park) and Bermondsey, near Chambers Wharf –from 5 June
- Deptford (Borthwick Wharf) and Bermondsey (near King’s Stairs Gardens) – week commencing 13 June
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 proposed Thames Tunnel is a sewer up to 32km long which needs to run from west to east London, up to 75mbelow ground, broadly following the route of the River Thames.
It is needed to help capture the 39M.t of untreated sewage which are discharged each year into the River Thames via combined sewer overflows (CSOs), and transfer it to Beckton Sewage Works for treatment.
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 programmed completion in 2020.