What is a Screw Pile?
Steel screw piles are the most cost effective foundation type available in the domestic and commercial construction industry.
They are also the most rapid in installation, as well as causing the least disturbance to the soil profile during installation, eliminating the costly and time consuming removal of spoil.
The pile consists of a high tensile 350 to 400 Grade steel shaft, with a single or multiple helix plate welded to the base of the shaft and a point of attack "bit" at the end, to assist in penetrating the soil profile. The pile is screwed into the soil profile by a hydraulic drive motor which is suspended off the boom of the excavator.
A pressure gauge is mounted in the cab for the operator to read the "torque" being generated as the pile is screwed into the soil profile. The torques are measured and recorded by the installer on the engineer's project log. The design requirements for the torques are test proven from soil bearing capacity to torque relationships which are related to Static Load results and C.P.T. comparisons.
The number and sizes of the helixes used is a function of the soil profile, with deep firm clay profiles requiring large plates and 2 to 3 helixes. This reduces the depth the pile would have to go, with conventional piles having to penetrate deeper into the profile. This "gearing" principle gives the screw pile considerable design flexibility. Shallower soil profiles over rock would require a small single helix plate.
The screw pile is a "displacement" pile, which as the title suggests, displaces soil as it screwed into the ground much the same as a timber screw is screwed into a plank. Unlike bored piers and driven piles, 90% of the load is generated from the helix plate at the base. Unlike bored piers and CFA piles, no spoil is excavated or removed from site, eliminating the potential issue of contaminated soils. Also due to the relatively slender shaft diameter, it far less likely to hit obstacles within the profile. Unlike driven piles, there is no vibration at all from the installation process.