Screwpile Australia - Design Information

Design Information

The Screwpile system has been developed by Screwpile Australia through testing and development under University supervision and consists of a steel circular shaft and one or more steel helix's. The pile and helix's have been designed to take maximum use of the available soil capacity. The Screwpiles are installed by the application of torque at the surface and the foundation displaces the soil as it advances. This action results in compaction of the soil profile mobilising maximum side adhesion and end bearing resistance. Multiple helix's provide additional bearing resistance through soil profile for compression load.

The installation method eliminates soil removal costs.

A Screwpile is a vibration free displacement pile and is consequently suitable for use close to sensitive buildings or installations containing delicate instruments or services.

Load Capacity

The geotechnical strength and serviceability are determined using analytical methods suitable for displacement piles with a pile diameter equal to the shaft size and under-reaming equivalent to the helix size.

Piles may be founded in clays, silts, sand or on rock.

The piles are installed using an excavator rig with hydraulic motors generating up to 130,000Nm of torque.

The installation process is sensitive to the strength of the soil being penetrated. Changes in pile penetration resistance are registered by a change in hydraulics pressure, giving a continuous log of torque applied during installation. This provides a valuable quality control on the load capacity of each pile. This also means that piles can be founded in relatively thin dense layers unlike bored piles which are insensitive to the soil strength during installation. The extensive testing program conducted by Screwpile Australia has shown that a near linear relationship exists between installation torque and load capacity, for a given screwpile configuration.

Geotechnical Capacity

Pile Tests
Numerous full scale pile tests have been performed under University control in accordance with AS2159 on sands and clay. Data has indicated the performance of screw in foundations can be predicted using conventional Geotechnical theory.

Torque v Load Capacity
The testing program together with research carried out on work performed by Screwpile Australia indicates that an essentially linear relationship exists between the installation torque and load capacity. The installation torque is a measure of the shear and frictional resistance of the soil profile when calibrated against test data. Screwpiles have particular advantages over alternative tension piles due to the large ratio of under-ream diameter to shaft diameter.

Compression

Tension

Structural Strength

A Screwpile is designed in accordance with AS 2159 -1995 and AS 4100 -1990 for structural strength and serviceability. The load capacity is often limited by the torsional strength of the steel circular shaft component.

The effective length is determined in accordance with AS 4100 with due consideration being given to soil shear strength and helix location in the profile.

Corrosion allowance is made in accordance with AS 2159 -1995 Table 6.3 and 6.4 for the five exposure classifications described. The use of Screwpiles are not recommended for permanent installations in exposure classification "Severe" or "Very Severe" without special coatings or electro protection.

A minimum design life of 50 years is adopted, but greater longevity may be provided for particular applications upon request.

Refer - Safe Working Loads For Screwpile Foundations Table

Engineering Certification

All Screwpiles are designed and certified by Screwpile Australia certified practising consulting engineer in accordance with the relevant codes.