100 West Cromwell Road

Analysing foundation capacity and future-proofing structures

We enabled much of this project to reuse the existing piled foundations, using the principles set out in BRE EP75: Reuse of Foundations for Urban Sites (RuFUS). Walsh carried out a comprehensive back-analysis of the structure which justified, wherever possible, the reuse of the existing sub and super structures. Partial demolition and reconfiguration of existing structures allowed the erection of eight buildings up to a maximum of 31 storeys.

On the 31-storey tower, the Walsh Geotechnical team calculated that existing piles could be reused in conjunction with a new piled raft foundation and several additional new piles. An independent review of ground investigation data was carried out, as well as initial hand calculations to back-analyse existing pile lengths and check the overall factor of safety using the proposed piled raft system.

Following this, a PLAXIS 3D finite element analysis checked individual pile loads against ultimate capacity. Settlements and raft / pile spring stiffness values were extracted, allowing assessment of differential movements and providing data to feed into Walsh structural analyses. This delivered significant improvements to the predicted settlement along with solutions that minimised differential settlement problems.

We also specified a suite of material testing and surveying across the frame to ensure that the building had been constructed in line with the design drawings and it has sufficient durability for the design life of the new building. The car park is part steel and part concrete frame with only some areas future-proofed for upwards development.

The Walsh design consists of minimal weight RC flat slabs supported on a steel grillage above the existing frame. Where possible the existing frame has been justified to take the additional load however elsewhere the structure has been supplemented and strengthened. Careful phasing and construction details have been developed to minimise the effect on the operational car park and to ensure the construction route is kept clear. Due to the proximity of the rail lines, all residential blocks have been isolated from the car park structure using acoustic bearings.