geotech report · MCU15/0087

Slope Stability and Geotechnical Assessment
1 Natasha Avenue, Noosa Heads




        Very Low Risk: Acceptable. Manage by normal slope maintenance procedures.

        Low Risk: Usually acceptable to regulators. Where treatment has been required to reduce
         risk to this level, ongoing maintenance is required.

        Moderate Risk: May be tolerated by regulators (subject to regulator’s approval) but requires
         investigation, planning and implementation of treatment options to reduce the risk to low.
         Treatment options to reduce to low risk should be implemented as soon as practicable.

The decision as to the level of risk to be accepted or tolerated needs to be considered by both the
owner, consent authorities, insurance companies and other parties involved. The decision should be
based on a number of factors, not limited to: the cost of repair of structures, the legal ramifications of
accepting the risk, the effect of the consequences on people, and the future implications of damage to
structures to further development. Also required to be considered, though not covered in this
assessment, is the risk to the lives of people with access to the property. Ultimately the decision to
accept or remediate the risk is taken by the owner of the site. The following section presents a
summary of the slope stability hazards and a slope stability risk assessment for the site.

7.4. Identification of Hazards
The only significant hazard on this site is considered to be the instability of the dune escarpment. This
is the risk assessed in this report.

7.5. Property at Risk
The items at risk in this assessment are considered to be the proposed new residence buildings,
swimming pool, driveways, any proposed retaining walls and services.

We have also assumed that any retaining structures would be designed by a professional engineer in
accordance with the requirements of AS4678-2002: Earth-Retaining Structures and adequately
designed for earth pressures, surcharges and elevated ground water conditions. The adopted design
should also include drainage and maintenance measures.

7.6. Results of Risk Assessment for Dune Escarpment
7.6.1.      Instability Mechanism
The slope of the dune escarpment is currently lying at a slope of some 35 to 38 degrees. The surface
sands to a depth of some 2 metres consist of loose sands with an internal angle of friction of about 28
degrees. These surface sands are thus currently unstable and at risk of sliding. It is likely that the
vegetation that is holding the upper sands in place.

The deeper sands on the escarpment are dense to very dense with an internal angle of friction of
some 38 degrees. These deeper sands are marginally stable.

The failure mechanism is thus likely to be a translational slip of the loose sands down the interface
with the denser deeper sands.




Coffey
GEOTKPAR02068AA/A                                                                                        7
12 August 2015