Numerical modelling resulted in savings in excess of £1M for the developer of a commercial, residential and recreational complex in north London following a redesign of foundations.
Specialist geotechnical consultant Card Geotechnics recommended that a rafted structure be used in place of piled foundations after numerical modelling for the Tally Ho Corner development in Finchley.
Chiltern Investment Properties is developing the complex which includes two basement levels, a 14 storey residential tower, theatre, shopping and leisure facilities and a bus station. Card Geotechnics advised structural engineer Walsh Associates on the construction of a contiguous pile wall around the proposed footprint, the excavation of the two basement levels to over 8m below existing ground level and the construction of new substructures.
A large sewer at around 37m below the site and differential loading across the site called for extensive analysis of the soil structure. Finite element software was used to assess the effects of employing a raft foundation.
A composite ground model was developed to reflect the ground profile and soil properties across the site, with 2D finite element analyses undertaken of sections across the proposed development.
These allowed an assessment to be made in 3D of the likely settlements associated with the proposed construction, and of the loads and deflections likely to impact on the sewer.
The analyses highlighted two things. First, that a raft foundation could be employed to support the development without excessive differential or total settlements being generated within the structure. Second, the foundation would not result in unacceptable changes in load or displacement of the sewer.
Output generated from the finite element analysis assisted in the structural design of the raft. In conjunction with supplementary geotechnical investigation, it also provided an optimal design for the contiguous piled retaining wall surrounding the proposed basement.