How do you tackle safe, sustainable construction – when you’re building on top of a railway tunnel?

Posted by Derek Mason

17th March 2020

Opposing views on Olympics-driven regeneration abound, but no-one can deny that the London 2012 Olympics site in Stratford has undergone an astonishing transformation.

What was once a post-industrial mix of abandoned factories, wasteland and railway sidings has now become home to the largest new urban park built in Europe in the last 150 years – Queen Elizabeth Olympic Park. And one of Europe’s largest shopping centres is here too.

Now the area between the park and Westfield is undergoing development to become a residential and commercial hub.

Known as the International Quarter London (IQL), this commercial, retail and office space project has a contract value of £2.4 billion. Key tenants such as Transport for London and the Financial Conduct Authority have already moved in, and a planned arts quarter will house buildings for the BBC, Sadler’s Wells, the V&A and the London College of Fashion.

But the building most of interest for its structural challenges is the pavilion, which is being built on top of the Stratford District Light Railway (DLR) tunnel. It’s a tricky location, with limited space for foundations.

So the question is, how do you construct a two storey building that needs to house the Olympic Park visitor centre, two restaurants, a cafe and a rooftop terrace, when your site is above a tunnel?

Answer: With prefabricated timber

Using timber not only means the structure is lighter, but it also means that minimal numbers of workers need to be present on site. Andrew Tobin, the IQL project director has been quoted as saying, “It’s a very quiet construction site, it’s like someone building some Lego behind you.”

He also said, “There isn’t a lot of timber construction around, but it’s something that we are looking at doing a lot more of. Because it’s over the top of the tunnel, we needed that was much lighter, with smaller footings and foundations.”

The project has just eight workers and one crane driver on site, but because the timber is pre-fabricated – and labelled with tags so it’s easy to see what should go where – the pavilion is going up fast.

The sustainably sourced timber is being used alongside steel beams and additional steelwork, especially in the building’s basement. This is needed due to the weight of the stairs and the crowd-loading expected once the space is open to the public.

A key structural challenge was the location of the DLR exclusion zone, which limited foundation depths. As a result, the substructures only go to about a metre deep. Workers put in a series of ground beams and poured concrete in between, to create a honeycomb effect.

The team also used a 3D modelling map to plan sheet pile depths that wouldn’t stray into the exclusion zone.

It’s a simple to assemble yet enormously challenging project, which is now due to be completed late on in 2020. And it’s exciting to see this additional phase of regeneration on a site I worked on between 2008 and 2012.

If you’ve read my book, Will it Stand Up? A Professional Engineer’s View of the Creation of the London 2012 Olympic Stadium, you’ll know that I led the team that did the third-party check for the Structural Engineering and Technical Review of the London 2012 Olympic Stadium.

And I was lucky enough to be able to give Sebastian Coe a copy when I met him at a business event – a particularly memorable moment since he is an Olympic medallist and was chairman of the winning London Olympic bid team.

Meanwhile, if you need assistance with the structural elements of an upcoming project, please do get in touch.

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