The former Technology Campus of Leeds University is in the heart of the city’s university area. The new development comprised the construction of a 19-storey tower on top of a part existing basement structure, to provide high-quality student accommodation along with public realm enhancements and a roof terrace.

Some ground investigation had been conducted before our involvement, but to gain a better understanding of the shallow soils, we completed additional investigation within the existing basement using the smallest available rotary drilling rig. This confirmed the presence of siltstone directly beneath the concrete basement slab. GEA completed a review of the existing ground investigation data to assess the ground conditions, their engineering properties, and the differential movements between sections of the building supported by raft and pile foundations. Initially, piled foundations were considered, but we were asked to evaluate the potential for reusing the existing raft foundation. Preliminary calculations by GEA, in collaboration with Ian Black Consulting (IBC), indicated that reusing the raft foundation was a feasible option and on this basis, IBC conducted a more detailed structural analysis. The proposed approach involved using piles on the eastern half of the site and a raft foundation on the western half.

An assessment of ground movements resulting from the proposed building was carried out using P-Disp and that the differential movements between the piled area and the existing raft were within acceptable limits.

The basement extension was constructed using contiguous bored pile walls, while the existing basement raft slab was retained and over-slabbed in areas where minor level adjustments were required. The piled section of the structure is supported by 161 piles, each with a 600mm diameter.

Our final task was to verify the quality of the imported topsoil used in the limited landscaped areas. Testing confirmed that it was free from elevated contaminant levels and met the residential area guidelines for plant uptake. Consequently, it was deemed safe and suitable for its intended purpose.