Slope Stability Report

Dean & Vanessa McDonald                                                                                       21505-001-Rev0
                                                                                                              4 February 2022

 Table 1: 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 (Ref. Section 2), and subject to the implementation of
recommendations given in Section 4, it is assessed that there would be a Low (L) Risk of global slope
instability affecting the proposed shed. 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 2 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).
 Table 2: Details of Qualitative Risk Assessment for Property (AGS 2007)

                                               Assessed
 Hazard               Likelihood Consequence
                                                 Risk     Comments

                                                          The likelihood of a failure through the existing cut batters or fill
                                                          embankments adjacent to the building platform is considered
 1: Failure through
                                                          Unlikely, given the favourable topography, lack of groundwater, lack
the existing cut
                       Unlikely   Medium         Low      of evidence of existing natural instability and subject to implementation
batters or fill
                                                          of the recommendations specified in Section 4. The consequence of
embankments
                                                          such a failure would remain Medium, with the resultant risk being Low
                                                          as per AGS 2007.

                                                          The likelihood of a deep failure through the weathered rock is assessed
 2: Deep failure
                                                          as Barely Credible due to the strength of such materials, and no
through weathered      Barely      Major       Very Low   evidence of deep-seated instability in the area. Although the
rock below the        Credible                            consequence of such a failure could be Major, the resultant risk would
foundation depth
                                                          be Very 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.




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Dean & Vanessa McDonald 21505-001-RevO

4 February 2022

 

Table 1: Stability Risk Levels

 

 

 

 

 

 

Risk Level Example Implications(1)
Very High Unacceptable without treatment. Extensive detailed investigation and research, planning
VH ery Tg 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 are . , : : :
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.
5 Usually acceptable to regulators. Where treatment has been required to reduce the risk
L Low Risk ~ A ~ .
to this level, ongoing maintenance required.
VL very Low Acceptable. Manage by normal slope maintenance procedures.

 

 

 

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 (Ref. Section 2), and subject to the implementation of
recommendations given in Section 4, it is assessed that there would be a Low (L) Risk of global slope
instability affecting the proposed shed. 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 2 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).

Table 2: Details of Qualitative Risk Assessment for Property (AGS 2007)

 

Hazard

J Assessed

Likelihood|Consequenc Risk Comments

 

1: Failure through
the existing cut
batters or fill
embankments

The likelihood of a failure through the existing cut batters or fill
embankments adjacent to the building platform is considered
Unlikely, given the favourable topography, lack of groundwater, lack
Unlikely Medium Low of evidence of existing natural instability and subject to implementation
of the recommendations specified in Section 4. The consequence of
such a failure would remain Medium, with the resultant risk being Low
as per AGS 2007.

 

2: Deep failure
through weathered
rock below the
foundation depth

 

The likelihood of a deep failure through the weathered rock is assessed
as Barely Credible due to the strength of such materials, and no

Barely Major Very Low | evidence of deep-seated instability in the area. Although the
Credible consequence of such a failure could be Major, the resultant risk would
be Very 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.

 

tectenic

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