Screw Piers are a steel screw-in piling and ground anchoring system used for building foundations. They are sometimes referred to as; screw piles, steel screw-in foundations, helical piles, screw anchors, screw foundations and helical piers.
Steel foundations first appeared in the 1800s as pile foundations for lighthouses, and were extensively used for piers in harbors.
Modern screw pier load capacities are in excess of 2000kN, (approx. 200 tonne). Large load capacity screw piers may have various components such as flat half helixes, Bizz alloy cutting tips and helixes, cap plates or re-bar interfaces for connection to various concrete or steel structures.
How Do They Work?
The pile shaft transfers a structures load into the pile. Helical steel plates are welded to the pile shaft in accordance with the intended ground conditions. Helixes can be press formed to a specified pitch or simply consist of flat plates welded at a specified pitch to the piles shaft. Screw pier design is based on standard structural and geo-technical principals.
Screw pier steel shaft sections are subjected to design parameters and building codes standards for the region of manufacture. They can be applied for loads up to 200 tonnes and the length of the screw piles can exceed 30 meters.
The number of helixes, their diameters and position on the pile shaft as well as steel plate thickness are all determined by a combination of:
The combined structure design load requirement
The geo-technical parameters
Environmental corrosion parameters
The minimum design life of the structure being supported or restrained
Screw piers are wound into the ground much like a screw into wood. They are installed using various earth-moving equipment fitted with rotary hydraulic attachments. Machinery varies from skid-steer loaders to 5 tonne through 35 tonne excavators.
Rotary hydraulic power heads with torque capacities ranging from 5,000Nm to 300,000Nm are custom fitted using various boom configurations. Special drive attachments connect the screw pier to the machine. Correct installation techniques are paramount to meet engineered design load and settlement outcomes.