Geotechnical Stability Assessment · MCU19/0008

Project No. PG-2096                                                                                                              Page | 6
April 2019
Ref: PG-2096, 2019-02-21, GR VER 2
Andrew and Michelle Douglas – Geotechnical Stability Assessment - Proposed Residence, 22 Arakoon Crescent, Sunshine Beach




    7.1 Deep Foundations

A deep foundation incorporating a bored pier footing system is recommended for
the proposed developments and encountered subsurface conditions. It is
recommended piers be socketed not less 1.5m into the underlying medium dense to
better sand.

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 1. The
Rd,ug values given in Table 1 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 1
will need to be divided by a factor of safety of 2.5 to caluculate the maximum single
pile working load.

TABLE 1                ULTIMATE (UNFACTORED) PILE DESIGN PARAMETERS

                                                            Ultimate Unfactored End
                                                                    Bearing*                              Ultimate Unfactored Shaft
                     Material                                        (kPa)                                       Adhesion*
                                                                                                                    (kPa)
                                                                      >4D
               Very Loose to Loose                                    NR                                                    NR
 Sands
               Medium Dense                                           900                                                   30
 Notes:
 *Geotechnical strength reduction factor needs to be applied to these parameters.
 1. NR – Not Recommended.

Lateral Capacity

The lateral capacity of a pile is a function of many factors including the soil profile,
pile fixity and eccentricity, embedment length and other factors such as failure
mode, strength of the pile and the shear strength of the surrounding founding
materials.

Horizontal pile capacities will be provided by passive resistance from the weathered
rock strata. However, the capacity from the soils should be neglected, given their
potential for creep.