engineering · 132001.210327.1

                                                                                                            ABN 51 640 311 842
                                                                                                                      CONTACT
                                                                                                              arcosgroup.com.au
                                                                                                                       OFFICES
                                                                                          Sunshine Coast | Brisbane | Gold Coast




diameter, depending on the design method adopted. Detailed settlement modelling should be undertaken as
part of the detailed design.
It is important that the installation of steel screw piles be carefully controlled in the field to ensure the pile does
not “over-screw”. Where over-rotation occurs, the bearing capacity for the helix would be substantially reduced
and/or pile movements incurred.
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. Measurement of installation
torque should not be relied upon to indicate pile capacity, as it has been documented that significantly
misleading results can be obtained. For this reason, piling contractors would be responsible for assessment
of actual pile capacities for their piles.
Structural capacity of the steel screw pile should be checked, and due allowance made for inclined or eccentric
loads, and possible corrosion effects.
Lateral capacity of steel screw piles could be increased by constructing concrete pile caps or by using
proprietary head attachments which are dragged into the soil providing additional lateral resistance at the pile
head.
Alternatively, cast-in-situ pile construction (ie. bored piles) could be considered but would need to be cased as
the very loose sand will be prone to collapsing in. Bored piles could be designed using the ultimate values
given in Table 2.
If footings are located adjacent to an underground service or other obstruction that is not homogenous with
the founding strata, the footing should be extended a minimum 0.3 m below an imaginary line projected at a
45 degree angle from the lowest point of the service/obstruction. This is depicted graphically in the following
diagram:




5.5 RETAINING WALLS
Retaining walls must be designed by a suitably qualified and experienced engineer and preferably in
accordance with AS 4678. The geotechnical parameters for use in design of either flexible or rigid wall systems
are presented in Table 3. Passive forces should be ignored in areas where disturbance may occur (ie. future
trenching or earthworks processes).




                                                                                                                        Page 8