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  Controlling the impacts of constructing a large diameter SCL tunnel on adjacent assets for Victoria Station Upgrade, London

  Victoria Station Upgrade (VSU) is a £741 million upgrade of the busiest station on London Underground and one of the UK’s strategic transport infrastructure assets. The Victoria Line is the busiest London Underground line with more than 100 million passengers per year. In order to minimise impact to the already stretched transport infrastructure, key requirements by the client were: the new works do not affect the safe operational of the Underground; road traffic is kept moving, including the buses and taxis using the Victoria Terminus Place bus station, and; the works do not disrupt the many utilities, or neighbouring businesses and residents. These requirements made the tunnelling works technically complex, with intricate geometries to suit the exceptionally constrained site . This in turn posed significant challenges for the project team, including the designers (Mott MacDonald), the ground treatment sub-contractor (Keller) and construction team (Taylor Woodrow Bam Nuttall JV). This paper describes one particularly challenging aspect of the tunneling works: design and construction of a 9m diameter, 30m long sprayed concrete lined (SCL) escalator barrel known as Paid Area Link (PAL) 10 (see. The SCL escalator tunnel described in this paper is unique in that is being excavated under very shallow overburden, the upper part of which is situated within water-bearing granular soils with just over 6m of ground cover. This section of the tunnel employs an annulus of jet grouted columns to stabilise water-bearing granular soils and exclude groundwater from the excavation. The escalator barrel then descends at 30 degrees through an existing concourse tunnel between the operational Victoria Line platform tunnels, with the lower section situated below the Grade II heritage listed Victoria Palace theatre (VPT) with only 2m of clay cover between the SCL and the water-bearing soils . To add to the complexity, the SCL

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