Technical Design

Classical formulae are used in the design of Instant Foundations 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 be considered.

 

Design criteria

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

Loads

Axial loads of 250 tonne can be achieved using a single pile. Loads can be compressive and/or tensioned. 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 reduce slenderness ratio of the pile.

Geotechnical conditions

Piling design should be proceeded by a thorough geotechnical investigation report. The report should include results and recommendations of founding level and strength characteristics of the strata.

Surface finish

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.

Corrosion

Each construction site should be assessed to determine the corrosivity of the prevailing soils. The Australian piling code, AS 2159-1995 has various requirements in respect of the corrosion of steel piles. Testing to be carried out include resistivity testing, acidity and chloride assessment. Sacrificial and electric anodes may be used to address corrosion.

Connections

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.