Reference Document - MCU24/0023

GJ Gardner Homes Gympie                                                                                          23236-001-Rev0
C/- Covey Associates Pty Ltd                                                                                       7 August 2023

landslide risk for the site. A summary of qualitative terminology for use in assessing risk to property is
attached (taken from AGS 2007).

It should be noted that this risk assessment excludes geotechnical risk that may be associated with settlement
due to consolidation of any uncontrolled fill materials over time which could affect non-piled structures (e.g.
pavements, landscaping structures). This risk assessment also excludes geotechnical risk associated with
the existing structures, dams, and areas of the site outside of the proposed residence area.
 Table 2: Details of Qualitative Risk Assessment for Property (AGS 2007)

                                                                   Assessed
 Hazard                               Likelihood   Consequence
                                                                     Risk
                                                                              Comments


                                                                              The likelihood of a failure through fill or natural soil is
                                                                              assessed as Unlikely due to the gentle to moderate
                                                                              ground slopes immediate to the proposed
 1: Shallow failure through fill or                                           development area and strength of the materials.
natural soil above the foundation      Unlikely       Minor            Low    The consequence of such a failure would be Minor
depth                                                                         considering the anticipated confined extent of
                                                                              instability, and the depth of foundations
                                                                              recommended, with the resultant risk being Low as
                                                                              per AGS 2007.


                                                                              The likelihood of a deep failure through low strength (or
                                                                              stronger) phyllite below the foundation depth is
                                                                              assessed as Rare due to the strength of these
 2: Deep failure through phyllite                                             materials, apparent lack of groundwater, and no
                                        Rare          Major            Low
below the foundation depth                                                    evidence of such existing deep-seated instability across
                                                                              the crest area. Although the consequence of such a
                                                                              failure could be Major, the resultant risk is Low as per
                                                                              AGS 2007.


                                                                              The likelihood of ongoing slope instability on the
                                                                              steeper, more poorly drained slopes is assessed as
                                                                              Likely due to the evidence of previous instances of
 3: Ongoing scours, slumps or                                                 such movement. Provided the residence is sited away
landslides on steeper slopes            Likely     Insignificant       Low    from those areas, and drainage and earthworks
and drainage lines.                                                           improvement measures are carried out as
                                                                              recommended herein, the consequence of such a
                                                                              failure would be Insignificant to the residential
                                                                              structure. The resultant risk is Low as per AGS 2007.




The potential impacts of slope instability on the proposed development have been assessed, and the
measures recommended below in Section 4 have been designed to mitigate those impacts so that a Low Risk
of instability would be achieved for the proposed residence.



4.0      RECOMMENDATIONS
General recommendations to help maintain the stability of the site are given in the document Some
Guidelines for Hillside Construction, which is attached.

4.1    Site Layout and Development Limitations
To achieve a Low Risk of instability for the proposed residence, the following is recommended:

     The building location must be moved to the north so that it is sited immediately atop the crest (Ref. Text
      Figure 12).
     All structures be founded on footings taken to penetrate through any fill and upper gravelly phyllite to
      socket at least 0.5 m into low strength (or stronger) phyllite.




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