Appendix B - Driveway Slope & Stability Assessment (Tectonic)

Contour Consulting Engineers                                                                                                    23038-001-Rev0
                                                                                                                                  6 March 2023

3.2     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 1 below, and
the Qualitative Terminology for Use in Assessing Risk to Property is attached.
 Table 1: Stability Risk Levels

 Risk Level                 Example Implications(1)

                            Unacceptable without treatment. Extensive detailed investigation and research, planning and
         Very High
 VH                         implementation of treatment options essential to reduce risk to Low; may be too expensive and not practical.
         Risk
                            Work likely to cost more than value of property.

                            Unacceptable without treatment. Detailed investigation, planning and implementation of treatment options
 H       High Risk          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 investigation, planning
 M       Moderate Risk and implementation of treatment options to reduce risk to Low. 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 to this level,
 L       Low Risk
                            ongoing maintenance required.

 VL      Very Low Risk 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 a Low (L) Risk of global slope instability
affecting the proposed driveway, with the works assessed to have a non-worsening effect on the existing
slope stability of the site, proposed areas of work and the adjoining properties. 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 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).

This risk assessment excludes geotechnical risk associated with the existing structures, dams and areas of
the site outside of the proposed driveway 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 driveway
 1: Shallow failure through fill or                                                           alignment and no signs of previous instability in that
                                           Unlikely              Minor            Low
natural soil                                                                                  area. The consequence of such a failure would be
                                                                                              Minor considering the anticipated confined extent of
                                                                                              instability, with the resultant risk being Low as per
                                                                                              AGS 2007.

                                                                                              The likelihood of a deep failure through stiff/medium
                                                                                              dense (or stronger) natural soil or weathered rock is
                                                                                              assessed as Rare due to the inferred strength of these
 2: Deep failure through
                                                                                              materials, apparent lack of groundwater, and no
stiff/medium dense (or stronger)             Rare                Major            Low
                                                                                              evidence of such existing deep-seated instability across
natural soil or weathered rock
                                                                                              the proposed development area. Although the
                                                                                              consequence of such a failure could be Major, 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 driveway.




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