Screw piles are a type of foundation, which are thought to have been invented in the 1830’s made from wrought iron with a view to supporting lighthouses and piers. Today, we make them using galvanised steel, meaning that the steel has been previously treated so that it will not corrode as quickly, we have also widened the structures in which this technology is used, so they are not exclusively used for lighthouses and piers now.
Put simply, it resembles a pipe with the way it looks, and it has one or more helices attached to it, how many and the spacing between each one is determined during the design stage. Helical is derived from the word ‘helix’ which means spiral, so the helical part of this structure is the spiral which is used to ‘screw’ the pipe into the ground. Each pipe has its helical flights specifically designed to suit individual ground types.
Special machinery is used to wind them into the ground, much like screwing a normal screw into some wood with a drill, but on a much larger scale. This type of foundation has no curing time, and therefore allows builders to begin building onto it as soon as the installation is complete, plus it can be installed in cold temperatures which would help lower any potential down time. Once the pile has reached the target depth (which again, is determined in the design stage specifically for each project) it will remain permanently in its place, and it is usually filled with concrete.
The bit of the structure which protrudes from the ground provides the connection to the building structure above, and can, in some cases increase the capacity of the pile. This interface between the pile and the building is a very important part of the design, and this requires a lot of care. The connection is designed by considering the building and the ground into which the piles are screwed into. The most common way to connect a screwpile to a structures foundation is to cast the head of the screwpile into the buildings concrete foundations. Fixing them in place is relatively easy, through steel reinforcing bars, which are cast into the piles and protrude out into the footing of the building.
They are very quick and easy to install, plus there is no excavation to cart away which will save you money, especially if there were contaminated ground to take away. They are also good for small areas as there is no set size, and every one is made specifically, plus they can be removed and re-used at any time.
Written by Jade Turney – Building Tectonics.