Contractors World

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Contractors World UK & Ireland
2011 Volume 1 Issue 8
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 • Seddon and Viaduct Housing Partnership building for the future.

 • GT Access Takes UKs First 15 m Hinowa Booms
 • Snorkel UK Appoints PLP Lift Trucks As Regional Dealer
 • A-Plant to Merge Lion Trackhire and Eve under New Name
 • Lendlease have renewed their framework agreement with Human Recognition Systems.
 • RPS Appointed for GWR Exeter Depot Expansion




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Contractors_World_UK_Lea Tunnel Major works begin


Major Thames Water Tunnel works begin

Work is underway on the Lee tunnel - a critical part of the Thames Water tunnel project, a scheme to virtually eliminate the need to allow untreated sewage to overflow into the River Thames. Many parts of the project are still in the planning stages but some works are in progress at a site called the Lea Tunnel

Bachy Soletanche Ltd in a joint venture with Morgan Sindall and VINCI Construction Grande Projets (MVB) poured the last diaphragm wall panel of the first shaft in February 2011. This diaphragm wall is 1500 mm thick, 89 m deep and reinforced top to bottom. Over 10,700 m³ of concrete has been poured and the same quantity of soil excavated and discharged directly into barges located on the Thames via a conveyor belt.

The verticality tolerance is 0.3%, which equals about 27 cm deviation at 89 m. To meet this constraint the cablette system was adopted to control verticality during excavation. The hydrofraise was also equipped with a gyroscope to act as a secondary system and once the bentonite in the panel had been completely replaced, a Koden reading was taken.

Contractors_World_UK_32 m deep caisson being excavated with Liebherr machinesThe Koden was newly purchased for the project and was fitted with a data port. For the first time, the contractors were able to produce a 3D representation of the diaphragm wall through an automatic processing of the digital data from the Koden. This data was then compared the results between the two cablettes, the gyroscope/cablette and the Koden reading.

With the hydrofraise moved out of the way at the first shaft, the fissure grouting could proceed unhindered. A grout curtain was installed for 11 m below the shaft with the TBM break-out zone being grouted at the same time.
Work began late September 2010 and the completion of the last shaft is planned for the end of 2011. Two hydrofraise machines have been mobilised to carry out these works.

Bachy’s geotechnical involvement in the project includes secant piling to two outfall shafts and the staff are spread throughout the project team to retain their involvement through to the end of the project in 2015.

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