St David's 2

The largest city-centre regeneration to ever take place in Wales, St David's 2 Cardiff is a mixed-use development that includes over 100 new retail outlets, 300 luxury apartments and parking for 3,000 cars, spread across a site footprint that is roughly the size of eight football pitches.

Ramboll UK took on this job as a design and build contract after it had already reached Stage D. Our key contribution has been rigorous testing of the scheme from first principles, resulting in a streamlined programme and cost savings that far exceeded client expectations.

The complex consists of a three storey steel frame structure supporting two concrete frame towers, one housing residential, the other car parking. Further parking is housed in the two-storey basement that extends across 30,000 sq m of the footprint. The site has a high water table and high seasonal rainfall.

We revised the initial massive basement design from a piled to a raft foundation solution, pushing the boundaries of existing geotechnical and structural design practice for founding at depth in Mercia Mudstone, and pointing the way to a best-practice model for founding in this type of geology.

Buildability was the single philosophical criterion that drove our analysis. Giken tubular and sheet piles form the basement retaining walls — a quick and minimised approach that eliminated the need for temporary works, reducing the excavation programme considerably. This is the largest-scale use of steel tubular/sheet piles in the UK to date.