Piled Foundation Re-Use and Strengthening Works at 1 Triton Square, Including Use of Intrusive Investigation, Numerical Analysis and Monitoring

1 Triton Square is a six-storey building with a one-level basement located within a commercial development near Euston, London. It was constructed by 1995 to a design by Arup Associates. The foundation scheme comprised straight shafted London Clay piles of 1.2m and 1.8m diameter between 12m to 18m in length arranged singly beneath columns. An assessment of the potential for pile re-use concluded a high level of confidence in the future performance due to the detailed design and construction information available. A small number of intrusive geotechnical and structural investigations were carried out to further increase confidence in the re-use scheme. The scheme added three storeys typically, together with a five-storey infill in the central atrium area. As the new loads for the scheme are typically greater than the capacity of the existing piles, an optimised strengthening scheme of small diameter piles installed within the existing basement combined with a retro-fitted raft was adopted. The settlement developed under the new loading was estimated using a three-dimensional finite element model. Movement monitoring and contingency plans were in place; however movement of the structure was within predictions.