Appendix E - Geotechnical Report

                                     PROPOSED RECONFIGURATION OF A LOT
                                     216 BLACK MOUNTAIN ROAD, BLACK MOUNTAIN

6.1.2         Qualitative Stability Assessment
The risk assessment for this project has been carried out following AGS 2007 Practice Note Guidelines for
Landslide Risk Management. Relative levels of risk and their implications are given in Table 2 below, and
the Qualitative Terminology for Use in Assessing Risk to Property is attached in Appendix C.
 Table 2: Stability Risk Levels

 Risk Level                Example Implications(1)
                           Unacceptable without treatment. Extensive detailed investigation and research, planning
        Very High
 VH                        and implementation of treatment options essential to reduce risk to Low; may be too
        Risk
                           expensive and not practical. Work likely to cost more than value of property.
                           Unacceptable without treatment. Detailed investigation, planning and implementation of
 H      High Risk          treatment options required to reduce risk to Low. Work would cost a substantial sum in
                           relation to the value of the property.
                           May be tolerated in certain circumstances (subject to regulators’ approval) but requires
        Moderate
 M                         investigation, planning and implementation of treatment options to reduce risk to Low.
        Risk
                           Treatment options to reduce to Low risk should be implemented as soon as practicable.
                           Usually acceptable to regulators. Where treatment has been required to reduce the risk
 L      Low Risk
                           to this level, ongoing maintenance required.
        Very Low
 VL                        Acceptable. Manage by normal slope maintenance procedures.
        Risk
 Note: (1) The implications for a particular situation are to be determined by all parties to the risk assessment and may
 depend on the nature of the property at risk; these are only given as a general guide.



Considering the existing site conditions, and subject to the implementation of recommendations given below,
it is our opinion that there is a Low (L) Risk of global slope instability affecting the proposed subdivision.
Regulators (NC) normally require that a Very Low or Low Risk of landslide affecting property must be
demonstrated to enable development approval. Summarised in Table 3 below is our qualitative assessment
of landslide risk for the site. A summary of qualitative terminology for use in assessing risk to property is
attached (taken from AGS 2007) in Appendix C.
 Table 3: Details of Qualitative Risk Assessment for Property (AGS 2007)

                                                                    Assessed
 Hazard                              Likelihood   Consequence
                                                                      Risk
                                                                               Comments

                                                                               The likelihood of a relatively shallow failure through
                                                                               the stiff (or stiffer) residual soils is assessed as Rare
                                                                               due to the gentle to moderate ground slopes (in the
 1: Shallow landslide in stiff (or
                                                                               vicinity of the proposed building envelope), strength
stiffer) residual/extremely
                                       Rare         Medium            Low      of these materials, apparent lack of groundwater,
weathered soil materials above
                                                                               and anticipated scope of future earthworks for
the foundation depth
                                                                               residential construction. A potential Medium impact
                                                                               from such instability is assessed, with the resultant
                                                                               risk to be Low as per AGS 2007.


                                                                               The likelihood of a deep failure through the very low
                                                                               strength (or stronger) phyllite is assessed as Barely
                                                                               Credible due to the lack of evidence of such
 2: Deep seated landslide
                                      Barely                                   instability on the site, and through the surrounding
through the weathered phyllite                       Major          Very Low
                                     Credible                                  area, combined with the strength of the material
rock below the foundation depth
                                                                               encountered. A potential Major impact from such
                                                                               instability is assessed, with the resultant risk to be
                                                                               Very Low as per AGS 2007.




19 June 2018
Report No. 17427-001-Rev0                                       7