Attachment 2 - Geotechnical Stability Assessment

Project No. PG-2096                                                                                          Page | 6
May 2022
Ref: PG-2096, 2019-02-21, GR VER 4
Clare Design – Geotechnical Stability Assessment - Proposed Residence, 22 Arakoon Crescent, Sunshine Beach




7.0 BUILDING FOUNDATIONS

Foundations

In order to provide a uniform and stable foundation and due to the site stability
issues, it is recommended a deepened foundation, incorporating either
appropriately founded pad footings or piers founded into medium dense or better
sands be adopted for the proposed constructions. Pad footings should socket a
minimum depth of 0.9m into the medium dense or better sands and piers should
found a minimum of 1.5m into the medium dense or better sands, if adopted.

Lateral Forces

In view of the global stability in the area, sloping natural terrain and the presence of
loose sands, it is recommended that all footing systems be designed to
accommodate forces due to potential soil creep within the surficial fill strata.

The potential lateral force due to creep in the soil strata may be determined from
the following:

Force                  =           1.5KpH2D

Where Kp               =           2.5

         =           Soil Density=20kN/m3

            H          =           Depth of sands, a depth of up to 2.8m was indicated in
                                   the boreholes. Final depth subject to further
                                   geotechnical assessment at time of pier excavations.
            D          =            Footing/Pier Width (m) - perpendicular to slope



    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