ICE London Civil Engineering Awards 2013

Tottenham Court Road Station Upgrade: Central Line Overbridges and Northern Line Interchange Tunnels and Escalator Decline

Principal Contractor: Taylor Woodrow BAM Nuttall
Client: London Underground
Lead Designer: Halcrow Group Ltd
Sprayed Concrete Lining Designer: Dr Sauer & Partners Ltd
Temporary Works & Sprayed Concrete Lining Designer: OTB

The Tottenham Court Road Station Upgrade (TCRSU) is one of London Underground’s (LU’s) largest station expansion and modernisation programmes. Opening in 2016, the new station will accommodate 200,000 passengers per day, with step-free access from street to train.

In December 2009 LU awarded Taylor Woodrow BAM Nuttall Joint Venture (TWBNJV) the contract to carry out the works. The JV employed Halcrow Group as principal designer.

Over 250m of sprayed concrete lined (SCL) tunnels have been excavated between existing 100-year-old station structures, usually running live with trains and passengers. Complexities included the small surface site, important road junction location, and sensitive third party assets.

Central line overbridges
This phase encompasses the two new overbridges constructed above the existing Central line platform tunnels. These will expand capacity for pedestrian access from a new Central line passenger tunnel to the platforms. Construction began in February 2012 and was completed in June 2012.

The platform tunnels are twin bores, with cast iron (CI) segmental linings, lie below a large Victorian brick sewer, less than 2m above the crown of the overbridge. The sewer could not be moved, or disturbed without risking leakage. The solution developed included driving a series of horizontal spiles from the adjacent Royal Mail parcel tunnel to form a support raft beneath the sewer.

In the original design, the overbridge tunnel was to be driven using traditional timber handworks. However, the JV developed an alternative design, from a value engineering scheme from Temporary Works designer OTB, with Halcrow and Dr Sauer, the SCL designer. This utilised a machine-excavated shotcrete cavern spanning the platform tunnels. After excavation to expose the tunnel’s outer face, concrete saddles and abutments were constructed in readiness for installation of the bridge decks - all undertaken while LU operated a full service in the tunnels below. Finally, during two weekend closures, the CI segments in the crown of the platform tunnels were removed at the overbridge locations, concrete encased beams were installed, and cheek plates erected to seal off the platform areas at the tunnel crown.

Innovative design delivered substantial safety improvements (major reduction in manual work; eliminating working under an unsupported face), reduced settlement risk, and significant cost and programme savings.

The JV also identified an alternative route for a proposed service riser between the platform tunnels, eliminating risk to the adjacent sewer.

The keys to success were collaboration between client, contractor and designers, all involved in every stage of design and delivery; continuous liaison with highway authorities and other third parties; and timely public information.  

Northern line over bridges
This phase encompasses the Northern Line Lower Concourse, three cross-passages to the LU platforms and Crossrail station) and the escalator decline from the new ticket hall. Tunnelling began February 2012 and was completed in December 2012.

The 30-degree escalator decline was excavated as the project’s first post-demolition phase. This was then bridged by the diverted Charing Cross Road, enabling the previously split site to be unified. Preparatory works also included re-lining the existing platform tunnels, replacing the platform-side cast iron plates with vertical steel supports to create space for new staircases and lift shafts between the platforms. While platforms were closed to passengers, trains ran centimetres from the worksite.

Approximately 100m of new tunnels (diameters 4.5m to 11m) were excavated and supported by sprayed concrete lining (SCL). Methods included side wall drift in six stages for the 11m dia. concourse. The spoil has been either recycled as back-fill on site or beneficially re-used in quarry restoration.

Innovative designs and approaches enabled work to be completed to the highest safety and quality standards, with no unplanned disruption to station operation. Design changes by the Joint Venture, agreed with LU following detailed cost-benefit analyses, included the following first uses for LU:

- side wall drift, enabling the tunnel face to be closed faster
- steel fibre-reinforced SCL instead of traditional rib and mesh reinforcement
- dry pre-blended reinforced concrete supplied in silos (the UK’s first extensive use); this overcame the highly constrained site conditions and produced very high quality concrete
- spray-on polymer-based waterproof membrane, replacing traditional PVC sheet membrane
These delivered substantial safety improvements (major reduction in manual work; eliminating working under an unsupported face), reduced settlement risk, and significant cost and programme savings.
Keys to success included collaboration between client, contractor and designers, all involved in every stage of design and delivery (including frequent – sometimes daily – design review meetings); continuous liaison with highway authorities; and timely information to the local community.

Results
Innovative design and methodology solutions enabled work to be completed to the highest safety and quality standards, with no unplanned disruption to station operation. These innovations, with excellent programme and environmental management, supported by the project’s ‘Beyond Zero’ health and safety approach, made the overbridges safer, cheaper and less disruptive to build. This project phase, already influencing thinking on construction methods for future LU schemes, will enable significant, sustainable improvements to London’s physical and social environment, transport infrastructure and economy.

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