Screw Piles in Wollongong

No Australian government or peer-reviewed source we found says how screw piles are used to underpin an existing house, so this page cannot tell you they suit yours. What it can give you are questions for a contractor who proposes them.

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What screw-piles in Wollongong actually involves

A 2003 paper by Yttrup and Abramsson in Australian Geomechanics describes a steel screw pile as a shaft of circular hollow steel with a plate welded near its end, installed by rotating it into the ground with some downthrust, and says it resists load by shaft friction and end bearing at that plate. A 2007 conference paper by McPherson says the pile's strength depends critically on the bending strength of the plate. Both describe the pile. Neither describes its use under an existing house.

A steel pile with round plates along its shaft lying on grass beside a hollow at the base of a brick wall — screw piles, Wollongong. Illustrative example.

Questions to put to a contractor

Ask what site investigation sets the depths the piles will reach: McPherson says a comprehensive investigation, preferably using CPT methods, should be the basis for founding levels. Ask how the contractor will show the piles are adequate, since the same paper says measured torque relates to the soil the plate has already passed through and not to the soil below it, so a minimum torque is not enough as the only check. Ask how the piles will be joined to the existing footing and who designs that, because we found no source that says. And ask about licensing: underpinning or piering work above A$5,000 needs a contractor licence in NSW.

The state's soil-landscape report for the Illawarra Escarpment unit says special foundation designs may be required in areas of mass movement hazard. It names no pile type, and no source we read ties screw piles to Wollongong ground of any kind.