Appendix B - Geotechnical Assessment · OPW23/0179

 Project No. PG-10375                                                                                                  Page | 11
 June 2023
 Ref: PG-10375, 2023-06-09, LTR VER 1
 Michael Cullen – Geotechnical Investigation - Proposed Residence, 128 Gympie Terrace, Noosaville




The deep foundation system should be designed in accordance with the
recommendations of AS 2159-2009 'Piling - Design and Installation'.

The ultimate geotechnical strength (Rd,ug) of piles can be calculated using the
unfactored, ultimate shaft adhesion and end bearing values given in Table 4. The Rd,ug
values given in Table 4 will need to be multiplied by a suitable geotechnical strength
reduction factor (øg) to obtain the design geotechnical strength (Rd,g) of piles. In
accordance with AS2159-2009, the øg value must be determined by the designer, but
based on the anticipated site, design and installation risk factors, a øg value of 0.48 is
recommended. Higher values may be applicable with suitable supervision.

If working stress methods are used in the pile design, the Rd,ug values given in Table 4
will need to be divided by a factor of safety of 2.5 to caluculate the maximum single
pile working load.

TABLE 4                PRELIMINARY ULTIMATE (UNFACTORED) PILE DESIGN PARAMETERS

                                                              Ultimate Unfactored End
                                                                      Bearing*                      Ultimate Unfactored Shaft
                      Material                                          (kPa)                              Adhesion*
                                                                                                              (kPa)
                                                                L < 4D                   L > 4D
  Loose Sand                                                      NR                       NR                  25
  Medium Dense Sand                                               600                      900                 35
  Indurated Sand                                                 1800                     2700                 70
  Stiff Clay                                                      NR                       NR                  25
  Very Stiff Clay                                                 600                      900                 35
  Hard Clay                                                      1200                     1800                 50
  Notes:
  *Geotechnical strength reduction factor needs to be applied to these parameters.
  1. NR – Not Recommended.
  2. L – total pile length; D – pile diameter.

The above design parameters should be confirmed with additional assessment,
should a deep foundation system be adopted.

13.0 DEWATERING CONSIDERATIONS

Construction of the basement and foundation system will likely require dewatering.
The groundwater will need to be lowered to the top of the indurated sand which is
expected to be virtually impermeable. Groundwater was noted at approximately 1m
below ground level and excavation of up to 3m could be expected. Drawdown of
approximately 2m is therefore expected to be required.

Dewatering is typically achieved through the use of perimeter spears and internal
wells. Where the excavation extends through the indurated sand and exposes the
clays, dewatering would typically be achievable using base sump pumps to maintain
dry conditions.