Reference Documents - RAL22/0032

                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.




                                                                                          7/10
Document Set ID: 22374434
Version: 1, Version Date: 14/04/2023