Geotechnical Report

                                     PROPOSED UNIT DEVELOPMENT
                                     31 BOTTLEBRUSH AVENUE, NOOSA HEADS

Given the geology, topography and particularly the relatively gently sloping terrain of the sand dune across the
proposed development area, it is considered rare that a landslide could affect the proposed development.
Sand dune slopes are generally close to the ‘limit of equilibrium’ where the surface gradient is about 30°,
although possibly lower in the order of 26˚ to 28˚ for very loose sands. The limit of equilibrium is the ‘tipping
point’ to instability, where the factor of safety (FOS) of the slope is approximately 1.0. The FOS of a slope is
the balance (ratio) between the forces driving instability (e.g. soil weight, groundwater pressure) and the
resisting forces (e.g. soil friction and cohesion).
Considering the existing site conditions (Ref. Section 2), and subject to the implementation of
recommendations given below, it is assessed that there would be a Low (L) Risk of global slope instability
affecting the proposed development. Regulators (NC) normally require that a Very Low or Low Risk of
landslide affecting the property must be demonstrated to enable development approval. Summarised in Table
3 below is our qualitative assessment of landslide risk for the development site. A summary of qualitative
terminology for use in assessing risk to property is attached (taken from AGS 2007).


Table 3: Details of Qualitative Risk Assessment for Property (AGS 2007)
                                                                    Assessed
 Hazard                              Likelihood   Consequence
                                                                      Risk
                                                                               Comments



                                                                               Given the low to moderate natural gradients through
                                                                               the proposed building areas, and scope of the
Failure through very loose to                                                  proposed site works, it is considered Unlikely that a
loose fill and loose natural soils    Unlikely      Medium            Low      landslide would develop in these materials, subject
above the foundation depth                                                     to implementation of the recommendations in
                                                                               Section 4. Given a potential Medium impact from
                                                                               such instability the resultant risk would be Low as
                                                                               per AGS 2007.




                                                                               The likelihood of a deep failure through the medium
Deep failure through the natural                                               dense or denser natural sand is assessed as Rare due
medium dense or denser sand            Rare          Major            Low      to the gentle to moderate overall ground slopes through
below the foundation depth                                                     the building areas and no signs of any existing slope
                                                                               instability. Although the consequence of such a failure
                                                                               would be Major, the resultant risk is Low as per AGS
                                                                               2007.



The potential impacts on slope stability of the development components have been assessed, and the
measures recommended below in Section 4 have been designed to mitigate those impacts.




17 December 2020
Report No. 20370-001-Rev0                                       9