A model station
ED NEWMAN-SANDERS, technical director at Atkins, tells RAIL how an innovative ‘kit of parts’ solution has been implemented to construct Crossrail’s new station at Custom House
Crossrail contractors employ new construction methods at Custom House.
The new Crossrail station at Custom House in London’s Docklands presented a unique opportunity to deploy novel methods of design and construction.
Not only is it the only above-ground station being built in Crossrail’s central station, but it will welcome thousands of regional and international visitors to London’s largest exhibition and conference centre, ExCel London.
Due to open in December 2018, the station will also be an important transport interchange with the adjacent Docklands Light Railway (DLR) and local bus services, in addition to providing the focus for regeneration in the London Borough of Newham.
These factors gave the design brief of Custom House an added dimension, as its showpiece status meant it also had to embody Crossrail’s vision and identity. As it is not constrained by an underground setting, Custom House will serve as an inspiration for the whole project and the local community, and thus required iconic architecture.
The station development is made up of two parts: a new 24-hour public route from Custom House to ExCel and the Royal Docks; and the Crossrail station itself, consisting of an elevated concourse and ticket hall above an island platform.
The team behind the building of Custom House consists of Atkins, Laing O’Rourke, Arup and Allies & Morrison. The design, however, would have to take into account a number of constraints at the site, including: the existing DLR running along the southern boundary and remaining fully operational throughout any construction sequence; a busy footpath and congested Victoria Dock Road running along the northern boundary; and a public right of way running across the top of the site to link pedestrians between Victoria Dock Road, the DLR station and the ExCel conference centre. This had to be maintained at all times, and also accommodate people with reduced mobility.
Further constraints included the main site being bounded by the Victoria Dock tunnel portal to the west and the Connaught portal to the east. This meant that contractors on each contract had to temporarily work within the other sites’ boundaries to complete their work.
A line of high voltage cables also overhangs the DLR to the south of the site, stretching from pylons to the east and west of the station. While not overhanging the main station site directly, they were close enough to be a major risk to any lifting operations on the site.
“Our strategy for the construction of Custom House included pre-fabricated
Shifting construction activity from site to factory reduces health and safety risks and ensures more consistent and higher-quality production. EWMAN-SANDERS, Technical Director at Atkins
and standardised components, with a ‘kit of parts’ forming the platforms, columns, concourse slab and roof,” explains Newman-Sanders.
“This unusual and innovative approach had a number of advantages. It minimised work on site that, in turn, drove down programme time, preliminary costs and the impact on the local community.
“Off-site manufacture also required fewer deliveries and vehicle movements around the site, reducing the traffic, noise and effects on air quality.
“Shifting construction activity from site to factory also improves working conditions and reduces health and safety risks, while the more controlled conditions of the factory ensure more consistent and higher-quality production.”
The development of a pre-cast concrete solution brought other benefits to the construction phase, by allowing swifter installation by crane of repetitious units, a benefit made more acute by the proximity of live overhead power cables and the restriction this imposed on the construction sequence.
As the project’s main contractor, Laing O’Rourke fabricated these major components at its Explore facility in Nottinghamshire, then delivered them to the site for positioning and commissioning on a ‘just in time’ basis.
Laing O’Rourke’s operations director Steve Jones says: “This approach is revolutionising construction in the commercial sector, but this was one of its first applications in a major rail infrastructure project.
“The seamless integration of the ‘virtual’ design model and the off-site manufacturing plant allowed us to create highly precise major structural elements, delivered exactly when we needed them. It’s an innovative strategy that has great potential for the many railway infrastructure projects in the years ahead.”
As Crossrail’s only new above-ground station, designers Allies & Morrison had the opportunity to design the station as a free-standing building rather than an interior fit-out. While there was plenty of scope for architectural expression, the design would need to fit into the urban setting of Newham, and also reflect its role as an icon for the capital’s newest railway line.
The 18° angle between Victoria Dock Road and Freemasons Road which joins at the southern end of the station sets the structural layout for the building with this geometry expressed in the design, from the paving to the ceiling details.
The solidity of the pale concrete building is offset by a canopy above the concourse, constructed of a steel-framed grid
containing air-filled translucent ‘pillows’ to provide shelter and allow natural light to filter into the station.
Enhancements have also been made to the surrounding public area with a new landscaped area featuring plants, cycle parking and improved lighting.
Robert Maxwell, Allies & Morrison’s lead architect for Custom House, adds: “At its simplest, the form of building laid out at the southern end of Freemasons Road produces a tripartite architectural composition. The plinth, or base, consists of a continuous monolithic wall necessary for protection from vehicle collisions; the principle façade, or middle, the colonnade capped by the edge and balustrade of the concourse; and the roof, ETFE pillars supported on slender steel columns.
“Our arrangement of the station produces a simple, legible route from the entrance to the train doors. The upper level is intentionally generous and open in feel to aid orientation and route selection for passengers. This open aspect enables observation and passive surveillance for both those approaching and within the station.”
The concrete superstructure consists of a series of pre-cast reinforced concrete frames, columns and floor units, held together with a hidden concrete ‘stitch’.
The platform structure comprises precast concrete panels spanning a system of primary beams, supported typically by three of four lines of beams resting on piles, driven through four metres of soft alluvium ground below.
There is a naturally ventilated space below the platform for maintenance of services, including two 11kV cables powering the
Crossrail lines, drainage pipes and other electrical and communications services.
There are three new overhead footbridges linking the DLR, ExCel and the London Borough of Newham to the new station. All three structures comprise steel fabricated primary box beams with a composite slab cast on permanent pre-cast concrete planks. Of these bridges, the ExCel footbridge had the largest span and was installed using two cranes working in tandem.
The project team decided that using a gantry crane was the best solution in such a restricted area to mitigate the risk of using a mobile crawler crane so close to 400kV overhead power lines. Another benefit of using a gantry crane was its ability to track back and forth over the structure once completed.
Newman-Sanders adds that modelling all of the components at Custom House in 3D provided a valuable tool in improving communication between teams around buildability, site inductions, logistics,
The construction team was heavily constrained by the proximity of the Dockland Light Railway that runs along the entire length of Custom House’s southern boundary, and remained operational throughout the build. This is the view of the Crossrail site looking north from Custom House DLR station platform. LAING O’ROURKE. sequencing and health and safety. The 3D model was also digitally linked and synchronised with the project programme to visualise and plan the complex sequence of installation. This was in turn linked to Laing O’Rourke’s factory database.
By using unique QR codes on each component, the status of each of the 880 precast components could be tracked, planned and recorded from the design stage through to casting, delivery and installation on site.
Once on site, mobile devices were used to scan the QR codes, which then brought up the appropriate quality form for completion. This was an efficient way of carrying out all quality and health and safety checks, maximising traceability and simplifying the handover process.
Newman-Sanders concludes: “Using a ‘kit of parts’ approach, the close collaboration of Atkins, Laing O’Rourke, Arup and Allies & Morrison developed a solution that was elegant, durable, cost-efficient and safe to erect on the constrained site, with the majority of the fabrication process taking place in a controlled factory environment.
“The team not only overcame the unique challenges for design and construction presented by the site, but also delivered the iconic ‘ambassador’ for the new Crossrail network they were seeking.
Our arrangement of the station produces a simple, legible route from the entrance to the train doors.” ROBERT MAXWELL, Allies & Morrison’s lead architect for Custom House