A screw pile foundation consists of a steel tube fitted with a helix, mechanically screwed into the ground until it reaches a load-bearing layer. The principle is old; what has changed is the installation equipment and the way the work is controlled.
The pile is rotated by a hydraulic drive head. The installation torque measured as it goes down gives a direct indication of the resistance encountered: this reading, correlated with the depth reached, is what confirms the anchorage.
The helix transfers the load to the soil across its entire bearing surface. Its diameter is chosen according to the load to be carried and the type of ground.
Screw piles, also known as ground screws, suit several types of project:
A screw pile foundation is not a universal substitute for concrete. It makes sense where the load, the soil and site access allow it — and that has to be assessed case by case.
Some conditions remain unfavourable: shallow boulders, uncharacterised mixed fill, very concentrated loads. A ground investigation removes these uncertainties before any work is committed.
Check before any project: the type of soil, the load of the structure, access constraints for the installation machine, and the planning rules that apply to the project.
A foundation system should be judged on three criteria: the required bearing capacity, the actual ground conditions and the constraints of the site. An approved installer carries out this check before providing a quote.