RFI - slope stability reporting

RECOR Pty Ltd                                                                                           22393-001-Rev0
                                                                                                        26 October 2022

Table 2 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 2: 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 that a landslip would
 1: Failure through very loose                                            develop in these materials, subject to
to loose natural sands above      Unlikely      Medium             Low    implementation of the recommendations in
the foundation depth                                                      Section 4. It is assessed that there could be a
                                                                          potential Medium impact from such instability
                                                                          so 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)
                                   Rare          Major             Low    movements locally, no signs of any existing slope
sands below the foundation
                                                                          instability and apparent lack of groundwater.
depth
                                                                          Although the consequence of such a failure could
                                                                          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. Subject to
implementation of these measures during construction, it is assessed that there would be a factor of safety of
at least 1.5 against slope instability.



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
Should any revisions be made to the extent of the proposed development as described in Section 1.1,
Tectonic must review these prior to construction to assess if there are any impacts on slope stability.

To achieve a Low Risk of instability, the following is recommended:
          All footings must found below the zone of influence of the surrounding structures and infrastructure
           (including retaining walls).
          All retaining walls exceeding 1 m high and/or subject to surcharge loads must be engineer designed
           and certified, which must include an assessment of global and internal stability.
          Design and construction of footings shall be undertaken in accordance with Section 4.4.
          Formal drainage should be constructed to ensure all stormwater is directed away from the existing
           and proposed structures.

4.2       Earthworks
No earthworks details were available at the time of reporting; however, provided drawings indicate that cut
and fill earthworks in the order of about 1.5 m depth/height will be required. Isolated deeper excavations may
be required for underground footings and service trenches. Should proposed cuts/fills exceed these
quantities, Tectonic must assess the impacts on slope stability before construction.




                                                            8/13