Technical Design of Screw Piles
Classical formulae are used in the design of Screw Piles. The steel shaft is designed much like a steel column and the helix is designed using standard piling formulae considering the prevailing geotechnical conditions. Some effect of friction on the pile shaft may also be considered.
In Australia, the following standards are relevant to Piling works:
AS 2159-1995 Piling-design and Installation
AS 4100 Steel Structures
AS 3600 Concrete Structures
The Building Code of Australia
Axial compressive loads of 250 tonne can be achieved using a single pile. Loads can be compressive and/or tension. Piles can be grouped for larger loads and to reduce the effects of bending moments and eccentric loading.
Slenderness Ratio, Le/r
Pile effective length should be designed after consideration of the geotechnical conditions. Additional helices can be used to reduce the slenderness ratio of the pile.
Piling design should be preceeded by a thorough geotechnical investigation report. The report should include results and recommendations of founding level and strength characteristics of the strata.
Piles can be installed with a range of surface finishes to suit the design requirements. Such finishes can be mill finish, galvanised, anodised and epoxy painted.
Each construction site should be assessed to determine the corrosivity of the prevailing soils. The Australian piling code, AS 2159-1995 has various requirements with respect to corrosion of steel piles. Testing to be carried out include resistivity testing , acidity and chloride assessment. Corrosion may also be addressed using sacrificial anodes and electric anodes.
Where piles are longer than the maximum length available, a connection may be required to join piles on the construction site. Connections can be welded or bolted depending on circumstances.