Att 9 - Geotech and PASS report

                                                                                                            Page 9 of 13




Table 4: Ultimate (Unfactored) Screw Pile Design Parameters
                  Founding Material                                Ultimate Unfactored End Bearing Pressure*
                                                                                     (kPa)
                 Stiff natural silty clay                                               300
              Very stiff natural silty clay                                             600
Notes: * Geotechnical strength reduction factor or factor of safety required


Experience indicates that properly designed and constructed piles sized using the parameters given
above and appropriately factored are likely to undergo settlements in the order of 1% to 2% of the pile
diameter.

It is recommended that the installation of steel screw piles should only be carried out by experienced
contractors and that pile capacities should also be checked in the field by load testing after installation
is complete. Measurement of installation torque should not be relied upon to indicate pile capacity, as
it has been documented that this can lead to misleading results. The torque relates to the soil through
which the helix is passing and not the soil beneath the base of the pile.



8.7      Retaining Walls

Retaining walls should be specifically engineer designed in accordance with AS 4678-2002 (Ref 7).

The design of flexible and rigid retaining walls could be undertaken using a triangular pressure
distribution and the earth pressure parameters given in Table 5. Flexible walls are those which are free
to rotate or tilt (such as cantilevered walls) and should be designed using active (Ka) earth pressure
coefficient. Rigid walls are those which are restrained against rotation or tilt (ie. single
anchored/propped walls) and should be designed using the at-rest earth pressure (Ko).

Passive resistance (Kp) at the toe of the wall should be ignored in the zone where future disturbance
(eg. services trenches) could occur.

The effects of surcharge in the retained zone should be included by multiplying the vertical pressure
developed by the surcharge by the appropriate lateral earth pressure coefficient. Allowance should
also be made for the surcharge due to sloping crests if applicable.

Table 5: Earth Pressure Coefficients (non-sloping crest backfill)
                Material                         Unit         Friction         Active     At Rest          Passive
                                               Weight          Angle            Ka          Ko               Kp
                                                      3
                                               (kN/m )       (degrees)
 Engineered filling*                              19              26            0.40          0.55            2.5
 Medium dense natural sand                        19              33            0.30          0.45            3.3
Notes:    * Depends on filling material type and level of compaction. Assumes clayey material compacted under ‘Level 1’
         inspection and testing.




Geotechnical Investigation, Proposed Commercial Development                                          90151.00.R.001.docx
11-19 Hilton Terrace, Tewantin                                                                                 May 2017