5 Miles Street

Innovative piled raft solution enables superstructure to commence on programme

The substructure design of this project has seen Walsh overcome a number of challenges including a very small site, sensitive settlement requirements and a tight construction programme.

The combination of a restricted site next to a Network Rail viaduct and several existing buildings, plus a tight deadline to commence work meant that it was not possible to undertake a pile load test. Without such a test the contractor could only achieve the loads by using 1200mm piles, but the rig would have been too big for the site. Working with the geotechnical team, Walsh devised a piled raft solution utilising the high level ground to limit deflections.

Walsh director, Andy Stanford says “We have undertaken a number of similar projects with Urbanest and are experienced in finding innovative solutions and technologies like the piled raft platform to ensure the best possible results for this type of scenario.”

Elsewhere, as well as Walsh designing the core to be slip formed, the underground drainage was placed on top of the raft, due to the tight boundary site and water attenuation pipes were used instead of the typical attenuation tanks. In addition, working with frame contractor GetJar, concrete slabs were designed with mesh reinforcement.