Screwpiles can be referred to as screw piles, steel screw-in foundations, screw piers, helical piles, helical anchors, screw anchors, screw foundations and helical piers. Screw piles were first described by the Irish civil engineer Alexander Mitchell in a paper in Civil Engineer’s and Architects Journal in 1848 – however, helical piles had been used for almost a decade by this point. Screw foundations first appeared in the 1800s as pile foundations for lighthouses, and were extensively used for piers in harbours. Between the 1850s through 1890s, more than 100 screw-pile lighthouses were erected on the east coast of the United States using screw piles. Made originally from cast or wrought iron, they had limited bearing and tension capacities. Modern screwpile load capacities are in excess of 2000 kN, (approx. 200 tonne). Large load capacity screwpiles may have various componentry such as flat half helices, Bisalloy cutting tips and helices, cap plates or re-bar interfaces for connection to various concrete or steel structures.
More recently, composite technology has been developed and patented for use in small screwpiles. Composites offer significant advantages over steel in small screwpile manufacture and installed performance.
Screwpile design is based on standard structural and geotechnical principles. Screwpile designers typically use their own design software which has been developed through field testing of differing compression pile and tension anchor configurations in various soil profiles. Corrosion is addressed based on extended field trials, combined with worldwide databases on steel in ground corrosion.
Modern Use and Benefits
Screwpile foundations are still used extensively, and their usage has extended from lighthouses to rail, telecommunications, roads, and numerous other industries where fast installation is required, or building work takes place close to existing structures.
Most industries use screwpile foundations due to the cost efficiencies and – increasingly – the reduced environmental impact. ‘Screwing’ the foundations in the ground means that there is less soil displacement so excess soil does not need to be transported from the site, saving on transportation costs and reducing the carbon footprint of the project.
The main benefits of screwpile foundations include: shorter project times, ease of installation, ease of access, reduction of the carbon footprint, ease of removal when the foundations are no longer required, reduced risk to the workforce, and reduced costs.
They are also suitable for both tensile and compression loads, so they are also used for masts, signs, and retaining structures.