SUPERSEDED Reference Document

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Table 5: Ultimate (Unfactored) Steel Screw Pile Design Parameters
                                          Screw Piles
 Material                                 Ultimate Unfactored Shaft             Ultimate Unfactored End
                                          Adhesion* (kPa)                       Bearing* (kPa)
 Loose sand                               NR                                    NR
 Medium dense sand                        NR                                    450
 Dense sand                               NR                                    1,000
Notes: NR – Not Recommended;
       * Geotechnical strength reduction factor or factor of safety required.


Shaft adhesion should also be ignored for steel screw piles due to disturbance during installation.

The actual capacity of steel screw piles depends not only on the soil conditions but also on
structural considerations of the piles such as the strength of the helix and the helix/shaft joint. For
this reason, piling contractors would be responsible for assessment of actual pile capacities for
their piles.

Experience indicates that properly designed and constructed piles loaded as above are likely to
undergo settlements in the order of 1% of the pile diameter.

It is recommended that further drilling be carried out following demolition of the existing
residence to confirm the foundation conditions across the site.

6.5    Pavement Subgrade

Following bulk excavation and provided site preparation is carried out as recommended above,
it is expected that ground conditions underlying on-ground slabs will comprise medium dense
sand. For design of pavements and slabs founding on well compacted sand, a soaked California
bearing ratio (CBR) value of 10% is recommended or a modulus of subgrade reaction (k) of
55 kPa/mm.

Rigid pavements should be designed using a soil modulus of 30 MPa for short term loads and
25 MPa for long term loads.

For loaded areas of different proportion or different load intensity to standard wheel loads,
Douglas should be contacted for further advice. It should be noted that the given modulus of
subgrade reaction is for pavement design only, and is not applicable to raft foundation design.

6.6    Acid Sulfate Soils

       6.6.1    What are Acid Sulfate Soils?

Acid sulfate soils (ASS) are naturally occurring sediments and soils containing iron sulfides or
sulfidic materials, often located over extensive low-lying coastal areas, predominately below RL 5
AHD. These soils are generally found close to the natural ground surface, but may also be found
at depth within the soil profile.




Proposed Residence                                                                           229073.00.R.001.Rev0
13 Mermaid Quay, Noosaville                                                                            June 2024