geotech

                                    PROPOSED UNIT DEVELOPMENT
                                    9 BOTTLEBRUSH AVENUE, NOOSA HEADS

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 area, it is considered Unlikely
 1: Failure through very loose to                                          that a landslip would develop in these materials,
loose natural sands above the        Unlikely      Medium         Low      subject to implementation of the recommendations in
foundation depth                                                           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
                                                                           dense (or denser) natural sand below the proposed
 2: Deep failure through the                                               foundation depth is assessed as Rare due to the lack of
medium dense (or denser) sands        Rare          Major         Low      precedence of such movements locally, no signs of any
below the foundation depth                                                 existing slope instability and a lack of groundwater.
                                                                           Although the consequence of such a failure would be
                                                                           Major, the resultant risk is Low as per AGS 2007.


                                                                           The likelihood of a slip/failure through the temporary
                                                                           retention system (sheet pile wall, or similar) as outlined in
 3: Temporary instability through                                          Section 6.4, is assessed as Rare, subject to detailed
sheet pile temporary retention                                             design by a suitable qualified RPEQ engineer and
                                      Rare          Major         Low
system, or similar, as discussed                                           construction by a specialist contractor which accounts for
in Section 6.4.                                                            the required factors of safety against slope instability.
                                                                           Although the consequence of such a failure would be
                                                                           Major, the resultant risk is Low as per AGS2007.


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.

5.2.1        Quantitative Assessment
In order to estimate the factor of safety (FOS) against slope instability for the proposed development,
numerical analysis has been conducted using the software Slope/W. The ground surface profile has been
modelled using a combination of survey information, preliminary design drawings and slope angles
measured in the field by Tectonic. The analysed subsurface profile was compiled based on the results of our
subsurface investigation. Some inferences regarding subsurface conditions were made between test
locations. A minimum FOS value of 1.5 is the commonly adopted industry standard for long term conditions.

No groundwater was encountered at the time of investigation. Given the gradients across the site and highly
permeable nature of the sandy soil, development of shallow groundwater is considered unlikely. Should
groundwater seepage be encountered during construction Tectonic must be notified to assess the impacts
on temporary instability.

To replicate future landscaping, a surcharge load of 5 kPa has been applied upslope of the proposed
building. Although building loads were not available at the time of reporting; a gross building load of 30 kPa
has been applied to areas of the building likely founded using high-level footings. Other areas will be
supported by piled foundations in the underlying medium dense (or denser) natural sands.

Soil shear strength was based upon effective parameters which were estimated based on our interpretation
of the subsurface investigation results, while also considering the values recommended for similar materials
in Appendix D of Australian Standard AS4678-2002 ‘Earth Retaining Structures’. Adopted soil parameters
are shown on the Slope/W outputs presented in Text Figure 9 on the following page. Analysis was
undertaken for a specified range of entry and exit points that could impact the proposed development.

The analysed profile represents the critical section (i.e. ‘worst case’ scenario) for the proposed development,
which covers the deepest cut. Our analysis indicates that the proposed development will achieve at least the
required minimum FOS for long-term stability (i.e. 1.5).




13 July 2021
Report No. 21169-001-Rev0                                   8