Engineers
Tension Screwpile Design
For sand and clay sites there is no better option for ground anchoring than screwpiles. Installed correctly screwpile have the unique ability to generate high tension load capacity in relatively shallow ground, assuming there is some bearing capacity in the soil.
The approach to screwpile design in tension differs in principal between sands and clays. Clay sites tend to incorporate multiple helix configurations whereas sand sites often utilise single helical configurations, although this is not always the case. Economics can be a factor when assessing overall design. In some instances it may be more economical to increase the primary helix size in an effort to elimiate the need for a second helix. Again this is not always the case.
Correct installation procedures are paramount in assuring the ground is not disturbed during installation. Screwpiles are in part a displacement pile and as such improve the immediate soil density during the installation process. Failure to ensure disturbance is kept to an absolute minimum will effect the ultimate uplift load capacity of the installed screwpile and is likely to result in excessive pile deflections under load. All the more reason to ensure only "Accredited" Screwpile Australia installers install screwpiles.
Screwpile design and performance under tension is influenced by soil density and water tables. Both are primary considerations in design. Overburden cone effect and soils shears govern overall anchor design. In grouped anchor configurations close attention needs to be given to any group effect on cone pull-out analysis.
In cyclonic conditions flooding and subsequent soil saturation needs to be modelled in overall design as a typical senario in these conditions is heavy rain followed by strong cyclic wind loads. Whilst clay based materials may create a temporary waterproofing membrane at a certain depth, the likleyhood of the first 300-500mm of soil at the surface becomming saturated exists. In design calculations the first 500mm of overburden soil should be ignored.
Caution needs to be give to sites which contain rock at shallow depth. Sufficient overburden and soil density needs to be present prior to the rock stratum. Whilst our patented RET technology has the ability to engage cemented and weathered rock it is difficult to actively socket the rock and ensure no rock shear failure will occur. The use of RET should be lomited to compression pile sites.