Screw Piles

Screw Piles

AS 2159 -2009 Piling Design and Installation

Minmetals is able to offer a unique screw pile foundation system for a range of applications. Helicast is a wholly owned subsidiary of Minmetals.

This patented system is currently in the process of undergoing testing in order to be admitted into the following Australian Standard

AS 2159 -2009 Piling Design and Installation.

Helicast™ Screw Pile Features

The Helicast™ screw piles feature a multi turn cast steel helical made as a one piece 485Mpa minimum tensile steel casting. The versatile cast helix can accommodate a range of Pipe shaft wall thicknesses to handle higher installation torques when required to penetrate hard grounds at depth.

The multi turn helical on the screw pile allows it to be turned into the ground with impressive speed and accuracy and without the noise and vibration associated with driven piles.

Unstable upper layers, subject to heave and shrinkage, can be avoided by placing the helical assembly deeper than the unstable zone. The lack of major skin friction on the smooth and slender shafts prevents such soil movement from affecting the axial capacity / stability of the Helicast™ multi turn cast system.

Helicast™ Screw Pile Advantages

The following table compares Helicast™ screw pile and standard steel pile and outlines outstanding performance of Helicast™ screw pile.

Item Helicast™ Screw Piles Alternative Piling Methods
Design life Minimum 50 year design life Average of 30 year design life
Soil suitability Suitable for all soil types

Building on weak soils or difficult conditions
Suitable for selective soil types

Limit to weak soils. Large diameter plate helix or Bored Piers required.
Weather suitability Used extensively in cyclonic conditions with good tension loads. May not used in extreme weather conditions
Concrete requirement No concrete required

No curing time so loads can be applied immediately
Concrete required to stabilize piles for plate helix or bored piers.

Curing time required for concrete to achieve desired strength, up to 4 weeks.
Soil disturbance No spoil generated Spoil generated with bored piers.
Installation disturbance Vibration free and minimal noise Larger installation impacts with vibration/drilling of driven piles or bored piers.
Installation speed Efficient and accurate installation. The smaller multi turn helix is quicker to install.

Available for immediate use
Longer installation time required for larger plate helix screw piles.
Cost saving Reduce time and cost on site Larger cost on site
Bearing capacity Greater resistance to uplift and bearing Bulb effect of multi turn screw helix gives pile an improved load capacity factor of 1.8 to 2.2 times that of a plate helix in medium/dense sand and clays. Standard bearing capacity. Pile capacity limited to end load of pile. Plate helix needs to be approx. twice the diameter of a multi turn helix to carry the same load in dense sands and clays.
Space limitation Ideal for working within close proximity of trees and sites with limited spaces. Short interlocking piles for internal building repairs May not suitable for limited spaces. Joining of extensions slow and costly.
Foundation depth Multiple extensions suitable for deep piling Only available to designed depth

Cannot be extended
Availability in water No de-watering

Can handle high water table
Limited in high water table condition. Bored piers unusable with high water table due to collapsing soil.

Other key advantages of Helicast™ screw piles are outlined below

  • Pile capacity is verified against installation torque
  • Adjustable Pier Cap (also acts as ant cap)
  • Can be mechanically fixed to any steel or timber sub frame
  • Segmented sections for reduced head heights
  • Environmentally friendly
  • Inclement weather is not a factor for installation
  • Safe working loads to 2400 kN per pile