A helical pier is a square, steel staff that resembles a large screw. It is inserted beneath the foundation of a building to support it. A helical pier is often installed when the soil is unstable and there is a danger of a sinkhole forming.
Helical piers are also installed during construction if it's determined that the structure needs an unusually deep foundation or is being built over an existing excavation.
Helical piers are installed by hydraulic drill motors coupled to small excavators for outdoor work. If the pier is installed indoors, it is installed by a portable jib. Though the specific depth depends on the job, the pier is installed an average of 20 feet deep.