geotech report · MCU15/0087

Slope Stability and Geotechnical Assessment
1 Natasha Avenue, Noosa Heads




Table 2: Summary of Pile Design Parameters


                                                                     Non Displacement Piles

                      Depth to Base of Unit
 Material Type                                       Average Ultimate Skin       Ultimate End Bearing at
                            (metres)
                                                          Friction fs                 Strata Base fb
                                                             (kPa)                        (kPa)

                                                            Not                          Not
  Fill Materials                NA
                                                        Recommended                  Recommended

                                                            Not                          Not
   Loose Sand                   0.5
                                                        Recommended                  Recommended

 Medium Dense
                                2.0                           25                          1500
    Sands

  Dense to Very          >4.0 (top of dune)                                               5000
                                                              40
  Dense Sands         >2.5 (dune escarpment)                                              4000


In order to assess pile capacity, a geotechnical strength reduction factor (Фg) should be applied to the
ultimate unit stresses in Table 2 in accordance with Table 4.3.2 of AS2159 – 2009. This code
requires the designer to evaluate the risk rating for nine factors which are listed in the table, and
calculate an average risk rating (ARR). This ARR is used to determine the basic geotechnical
strength reduction factor Фgb. This Фgb value is used for the geotechnical strength reduction factor
Фg, if no load testing is to be carried out on the piles. Where load testing will be carried out, AS2159
– 2009 allows the Фg to be increased.

Information on the project specifics, which would allow all nine risk factors to be evaluated, is currently
not available to Coffey. Consequently, this risk evaluation must be undertaken by the designer when
these details are known. That said, three of the risk factors relate to the site investigation, and
guidance on the risk ratings for these is provided in Table 3.

Table 3: Some Suggested Risk Ratings for ARR Calculation

                            Risk Factor1                                              Risk Rating

                   Geological complexity of the site                                          3

                    Extent of ground investigation                                            3

               Amount and quality of geotechnical data                                        3

Note: 1 – Refer to Table 4.3.2(A) in AS2159-2009 for details on risk factors.




Coffey
GEOTKPAR02068AA/A                                                                                          5
12 August 2015