Reference Document - Geotech Report - MCU24 0094 · MCU24/0094

                                       PROPOSED RESIDENCE
                                       33 ROSS CRESCENT, SUNSHINE BEACH

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 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,
                                                                                retention system proposed and proposed
 1: Failure through very loose to                                               protection of the eastern side of site using a
loose natural sands and sand fill                                               shear pile wall, it is considered Unlikely
                                         Unlikely      Medium          Low
above the foundation depth in                                                   that a landslide in these materials would
future building areas                                                           affect the proposed development. 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 foundation depth is assessed as
 2: Deep failure through the                                                    Rare due to the lack of precedence of such
medium dense (or denser) sands            Rare          Major          Low      movements locally, no signs of any existing
below the foundation depth                                                      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 failure of a temporary
                                                                                retention system, if required (sheet pile wall, or
                                                                                similar) as outlined in Section 6.3, is assessed
                                                                                as Unlikely, subject to detailed design by a
 3: Instability of temporary sheet
                                                                                suitably qualified RPEQ engineer, which
pile retention system (if required),
                                         Unlikely      Medium          Low      accounts for the required factors of safety
or similar, as discussed in
                                                                                against slope instability, and construction by a
Section 6.3.
                                                                                specialist contractor. Although the
                                                                                consequence of such a failure could be
                                                                                Medium, the resultant risk is Low as per
                                                                                AGS2007.

                                                                                While the modelling indicates it is Possible that
                                                                                an extreme erosion event will occur at the site,
                                                                                the likelihood of a landslide extending through
                                                                                the future piled wall system along the eastern
                                                                                edge of the building or site boundary as
 4: Retrogressive failure of the
                                                                                outlined in Section 6.0 is assessed as Rare,
high foredune face considering a
                                                                                subject to detailed design by a suitably
hypothetical storm and wave               Rare          Major          Low
                                                                                qualified RPEQ engineer, construction by a
scenario, impacting the subject
                                                                                specialist contractor, and considering the
site.
                                                                                results of our quantitative slope stability
                                                                                analysis outlined in Section 5.2.1. 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 6 have been designed to mitigate those impacts.




18 June 2024
Report No. 24096-001-Rev0                                       10