Compiled Reference Documents - MCU25/0091 (As Published)

            Wingara Hills Pty Ltd

            6.2 Stability Risk Assessment
            A qualitative slope stability risk assessment has been carried out following the Australian Geomechanics
            Society (AGS) Guidelines for Landslide Risk Management (March 2007). The risk assessment relates to
            property and potential development. Relative levels of risk and their implications are given in Table 2 below
            and the qualitative terminology (i.e. likelihood and consequence definitions) for use in assessing risk to
            property are attached in Appendix C.
            Table 1: Stability Risk Levels
              Risk Level                       Example Implications(1)

                                               Unacceptable without treatment. Extensive detailed investigation and research,
                                 VERY HIGH     planning and implementation of treatment options essential to reduce risk to
              VH
                                 RISK          Low; may be too expensive and not practical. Work likely to cost more than
                                               value of property.
                                               Unacceptable without treatment. Detailed investigation, planning and
              H                  HIGH RISK     implementation of 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
                                 MODERATE      requires investigation, planning and implementation of treatment options to
              M
                                 RISK          reduce risk to Low. Treatment options to reduce to Low risk should be
                                               implemented as soon as practicable.

              L                  LOW RISK      Usually acceptable to regulators. Where treatment has been required to reduce
                                               the 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.
            The risk assessment essentially involves combining the elements of ‘Likelihood’ and ‘Consequence’ for the
            potential hazards identified across the proposed development area in a qualitative manner. Relative levels of
            risk and their implications are given in Table 3.
            It should be noted that the stability assessment above relates to the global stability of the areas surrounding
            the proposed development (as shown in Figure 1). Our assessment does not include areas surrounding the
            existing residence.
            Table 2: Qualitative Risk Assessment for Property (Based on AGS 2007).

                                                                 Assessed
              Hazard              Likelihood   Consequence                         Comments
                                                                 Risk

                                                                                   The likelihood of shallow failure is assessed as Unlikely
                                                                                   due to the absence of groundwater (during our
                                                                                   investigation), the nature of the soils found in our
              Shallow failure                                                      investigation and site slopes directing water away from
              of soils above                                                       the proposed development. The consequence is
                                    Unlikely        Minor               Low
              the footing                                                          considered Minor, if the structures are lightweight/flexible
              zone                                                                 and founded well into the very stiff to hard extremely
                                                                                   weathered material or mudstone underlying weathered at
                                                                                   depths below about 1.2 m BGL as recommended in this
                                                                                   report. The resultant risk is Low.
              Deep-seated
              failure through
              very stiff to                                                        A likelihood of Rare is assessed for global instability due
              hard residual                                                        to the competent nature of the residual soils, weathered
                                       Rare        Medium               Low
              soils; extremely                                                     materials; and mudstone. A consequence of Medium has
              weathered                                                            been assigned, with a resultant risk of Low.
              material or
              weathered rock




            J002915-001-R-Rev0                                      7


Document Set ID: 24031832
Version: 1, Version Date: 14/08/2025