Piling Contractors in Sussex

The job was the foundation for a large rear extension to a house: a steel-framed structure on a piled raft slab. Twenty protected trees stood close to the works. Continuous flight auger piling was chosen as the most efficient method for the ground that was expected.

We installed 38 CFA piles at 300mm diameter, each founded in chalk and each carrying 60kN. Several bores collapsed in the upper layers at first. By drilling further into the chalk the bores lined themselves and held, and that technique was used on 11 production piles.

Six piles were drilled to practical refusal in the dense flint. Extra piles were added to make up for the reduced depths. Every pile had sonic integrity testing before the slab was poured.

The raft slab covers 116m² at 200mm thick, in C32/40 concrete with A393 mesh, over 225mm Cellcore void formers. Piling and foundations took about five weeks in all, and the job was delivered on budget.

Our knowledge of Sussex ground on this page is the Chichester job and nothing wider. The pile design there was based on British Geological Survey data. It showed made ground over sand and gravel, with chalk at roughly 4 to 6m depth.

On site the ground was far harder than that suggested. Extremely hard flint deposits wore down two lead augers and all of the follower augers, and the tooling had to be repaired twice during the programme. The lesson is plain: desk data is a starting point. A ground investigation of the site itself tells the engineer more before the piling starts.