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The technical lowdown on Chelsea's new stadium

Chelsea Football Club’s newly approved stadium project at Stamford Bridge is an incredibly complex job that requires innovative ways to maximise space including building over rail lines, according to its engineering director.

The £500M stadium has just been given the green light by London Mayor Sadiq Khan after gaining planning permission from Hammersmith & Fulham Council in January this year.

The existing 41,600 seater stadium at the site in west London will be demolished to make way for the construction of the new 60,000 capacity football stadium and an ancillary stadium.

The 6.2ha site is bounded by London Underground’s District line to the north-west, and the Southern mainline railway to the east. Currently, these lines are in open air cuttings, but to increase the capacity of the stadium, decks are being built over the top of the lines to allow the footprint of the stadium to be increased.

“It’s really complex,” said WSP Parsons Brinckerhoff director Bill Price. “One of the challenges is that it is a very constrained site and the only way the space can be made large enough is to deck over the railway lines.”

In the east, columns which support the stands and roof of the structure will be supported by the deck. To do this, the engineers will build two new parallel, reinforced concrete walls on either side of the railway cutting 11m apart. These will form the supports for the deck.

At the location of each of the columns, 1.2m deep upstand beams will span radially between the walls to pick up the point loads under the columns. The gap between the upstands will then be filled in to form a concourse area for the stadium.

“Right now the rail on the east is a relatively shallow cutting, we need all the air rights that they [Network Rail] will give us to be able to walk around the outside of it,” said Price.

“The existing walls are not much more than garden walls at the moment. Our new walls – to create the vertical line of support to the deck – will be much closer to the railway line, around 3m, to minimise the distance the beams have to span.”

In total around 500m of track will be decked over. Price said Network Rail had been “on board” with the design to move the walls closer to the tracks than the existing walls, and that this should not be seen as a barrier to constructing around rail lines.

“We are saying to clients: you don’t need all that land around the lines,” said Price. “Put the railway in a small space and then you’re maximising the space on the other side of the wall which is simpler to design for.

“It’s not that much more difficult to build close to it because you’re still adhering to the same strict rules as if you were building slightly further away.”

The roof of the stadium is being designed by both WSP and German consulting engineer Schlaich Bergermann. It will have a rectangular opening above the pitch and will be supported by 264 radial steel roof trusses that will span 50m over the stadium bowl. The trusses are supported by a steel tension ring arrangement which is supported by the same number of vertical concrete columns around the stadium’s perimeter.

Price said that the appearance of the stadium was also unique. The main columns around the perimeter of the structure will be clad in brick, but because the columns are up to 60m in height, he said that the brickwork cladding would most likely be constructed off site in panels rather than hand laid.

“Above ground, we’re looking at quite a few options for off-site manufacture,” said Price. “With a constrained site, we’re trying to simplify things and therefore the concrete columns are likely to be clad in masonry which has been preassembled on a concrete backing.

“We looked at hand laying the bricks, but there are quite a lot of bricks and the labour on site would be enormous coupled with the health and safety concerns of working at height.”

To keep the stadium at an acceptable height but increase its capacity, the pitch will be lowered by 5m. Below it there will be a vast basement housing kitchens, and parking for vehicles and television broadcast vehicles.

“We are completely excited to be working on this fantastic job,” said Price. “It’s an iconic design and unique in stadium terms.”

Aecom is strategic planner, WSP and Schlaich Bergermann are the structural engineers. Herzog & de Meuron is the architect.

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