For those that don’t know, Crossrail is a 118-kilometre (73-mile) railway line under construction in London and its environs.
It is expected to begin full operation in 2019 with a new east-west route across Greater London. Work began in 2009 on the central section of the line—a new tunnel through central London—with connections to existing lines that will become part of Crossrail.
It is one of Europe’s largest railway and infrastructure construction projects and WJ was trusted enough to secure work on the Crossrail Passages: the tunnels needed between the Crossrail TBM drive tunnels to house control equipment, sumps and for emergency evacuation.
The tunnel horizons in the East London area are situated within the Lower London Tertiaries deposits, with the tunnel invert found at varying levels within the London Clay, Lambeth Group and Thanet Sand formations. With excess pressures reaching up to 3 bar, WJ needed to employ a wide range of strategies to achieve the required depressurisation including: surface ejectors and deepwells, in-tunnel probing, wellpoints, ejectors and passive wells. Each scheme was tailored to the specific combination of ground profile, pore pressures and surface/tunnel access constraints prevailing at each cross passage.
Use of stuffing boxes and lost bit drilling was often essential to control ground loss for tunnel installations. In some cases, chalk dewatering was proved to be the best option for several adjacent cross passages, reducing the surface access requirements and overall cost. Something WJ constantly strives for.
A challenging and gratifying project, it was exciting to be involved in this innovative phase of London’s transport history.
- LOCATION: East London
- CLIENT: Crossrail
- MAIN CONTRACTOR: DSJV (Dragados Sisk JV)