Crossrail’s new £649M station at Paddington station in London is housed within a mighty box sunk under Eastbourne Terrace and Departures Road.
It is adjacent to the existing mainline station’s southern flank. Over 20m deep, the box is 24.4m wide and long enough to accommodate passenger platforms 208m long.
Key to successful delivery of Crossrail’s £649M station at Paddington was a small but complex arch connecting the new structure with Brunel’s 1850s mainline terminus.
A 90m length of the box top has been left open, under a steel and glass canopy built 9.75m above ground level, allowing light and air to penetrate to the new station below.
The new works are truly substantial in scale, even if comparatively straightforward to undertake (see photo below).
That said, a relatively small element of the new station infrastructure proved problematic and caused a disproportionate amount of angst. This was the “Crossrail Paddington arch”, which created a passageway through an existing building to link the old station with the new. The arch walkway is approximately 37m long by 11.5m wide, with a clear link height of 4.25m.
“We knew, obviously, that Crossrail Paddington couldn’t be handed over until the connecting arch was in place and open for use,” says Aecom director of building and places Mike Pauley.
Aecom is Crossrail Ltd’s design consultant for Paddington station and much else besides, along the Crossrail route, formally known as the Elizabeth line. The company has worked on Paddington since 2008.
There were unexpected constraints including uncharted pipes and other existing services, which had to be removed or correctly relocated.
“The arch is essential for passenger movement between stations and its completion was very much on Crossrail Paddington’s critical path.”
This proved easier said than done. There were a number of complex issues to address, among them breaching Macmillan House in a manner that suited heritage authority Historic England.
Macmillan House is a Grade I listed building apparently designed (as was Paddington Station) by Brunel for the Great Western Railway. It forms part of the mainline station complex, its front façade running alongside the full length of platform one’s southern side.
Visitors could leave Macmillan House, walk straight onto platform one and if they wished, catch a train.
The building had lain unused for many years but has now been refurbished to create office accommodation. Its significance for Crossrail was that Macmillan House formed a barrier between the old station and the site of the new one.
A German bomb during the Second World War had created a gap in the original structure of Macmillan House. It made good sense to remove what had been built to fill the gap after the war and use the space created to locate the new link.
Historic England approval
This plan was put to Historic England and gained its approval, along with that of Westminster City Council.
All was not to prove plain sailing, however. “Opening up Macmillan House revealed many hidden challenges,” says Aecom engineer (structures) Elton Yan.
“There were unexpected constraints including uncharted pipes and other existing services. All of which meant the new link’s design had to be reviewed.”
This was a worry: completing the Crossrail arch on programme was vital.
“The arch was so small a component in comparison to other of the station’s elements, but also so important,” says Pauley.
Crossrail Paddington’s contractor, the joint venture between Costain and Skanska, had initially been charged with the arch’s design but responsibility transferred to Aecom.
Familiarity with listed structure
This was due to Aecom’s familiarity with the Macmillan House structure – it had already carried out blast analysis on the façade and streamlining the workload helped to achieve better value. Even so, the redesign involved both parties, in intense collaboration.
The arch’s installation was scheduled to take place toward the end of the project and it was important to get everything right.
Service provision to the main line station had to be maintained at all times as did the uninterrupted operation of fixed mechanical and electrical plant.
The design review saw the modified Crossrail arch structure retain its basic simplicity, a frame of steel trusses and steel columns, the columns extending down to basement level and founded on concrete pads.
Abutting original station
It was planned that this structure would abut the original station – the frame’s northern end touching support walls from which Brunel’s iconic roof arches spring – and there had been concerns about possible detrimental impacts of the new on the old.
By the time installation of the Crossrail arch had begun, measures to safeguard the original structure had been established. The main precaution involved close monitoring of the original Brunel components.
The “range of motion” of these had been calculated, employing data collected for this purpose several years before. Armed with the range as an effective maximum/minimum benchmark, Aecom could gauge whether any new movement was getting close to harmful. A trigger level of 5mm was determined.
In the event, all went well. Crossrail Paddington station and its formerly bothersome connecting arch are now in the possession of Transport for London.
Comentarios