Frequently Asked Questions

Question 1

Why does my house have screw piles?

Answer

The question of why my house has screw piles is becoming an increasingly common question as more engineers are designing them into builds and more builders are realizing the benefits over a bored pier.

An engineer will design helical screw piles into a new build or renovation for several purposes:

The soil report indicates a P Classification; – P class soil is one that has a determined amount of soft soil that does not offer any structural integrity and the helical pile is designed to be screwed through the fill and support the dwelling on a more solid natural soil profile.
The soil report indicates H or E Classification; – H and E class soils are considered reactive type soils and with changing moisture conditions the soil can Heave or Swell creating problems through the house such as cracking floors, walls and ceilings. Soil reactivity is an increasing problem in Australia with changing weather conditions such a drought. A Helical pile is designed to be installed beyond the reactivity soil to minimise the effects of reactive soils and keep the house stable.
There are trees close to the build or trees that have been removed for the build; -Trees can create major structural issues with your build. A trees root system will change the surrounding soils behavior which can greatly affect the slab and therefore the house above it. Helical piles are used to be installed at a depth that the tree roots will not affect the house.
There is a sewer or stormwater close to the house; – A sewer or stormwater asset must be protected and measures out in place to protect it and the house should they need to be dug up and repaired in future.

Question 2

When are helical screw piles better than bored piers with concrete?

Answer

Helical screw piles offer distinct advantages over bored piers with concrete when;

The soils are likely to collapse when drilling pier holes
The soil profile shows deep piers required. (Screw Piles have a proven cost benefit once a bored pier is required to be deeper than 2700mm)
In sandy soil profiles. (Bored piers will often “blow out” in size in sandy soil profiles due to collapse.
In remote areas. (Helical screw piles are a lower cost to establish than bored piers with no need for concrete trucks, pumps or soil removal which can be expensive in remote areas.)
Limited Access is available. (A Helical screw pile can be installed when using the correct equipment with access as small as 1000mm wide.)
Helical screw piles have no soil removal required. (Part of the cost of a bored pier with concrete is removing the soil once the holes are drilled.

Question 3

How compliant are Helical Screw Piles?

Answer

Helical screw piles are governed and designed with 4 Australian Standards covering compliance. The compliance covers everything from the type and strength of the pipe to minimum standards for “load” and minimum depth requirements for poor soils and reactive soil. They must be designed to provide a minimum 50 year design life. Once the pile is installed the contractor must provide a detailed report to the inspector to show what the pile was designed to do Vs what it actually achieved on site.

Question 4

What are some of the applications a Helical screw pile can be used for?

Answer

Helical screw piles can be used for most slab constructed dwellings such as raft / beam and waffle slab in new builds. They can be used as “posts” for stump / bearer and joist constructed houses.

They are an ideal solution for renovations and extensions to existing dwellings with easy establishment and tight access ability.

They can be used for underpinning failing dwellings foundations where movement has occurred due to problematic soils created by trees, broken easements, reactive soils etc.

Question 5

What’s the difference between a “screw pile” and a Helical screw pile?

Answer

Helical screw piles have a continuous consistent pitch from the bottom to the top of the “helix” plate unlike others who have differing angles with either a 2-piece helix or more aggressive pitch helix.

A true Helical screw pile has been proven with 100’s of tests conducted globally to have less soil disturbance than other types of helix plates. Minimizing soil movement during installation is critical in ensuring the pile performs to the best of its designed requirement. By disturbing the soils more during installation you may risk effecting the actual and long term performance of the pile.