Attachment C - Soil Survey Report · MCU18/0013

Project No. 1-20119                                                                                                                                                Page | 15
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach




TABLE 4               SUMMARY OF RISK TO LIFE CALCULATIONS
                                                  Assessed
Hazard              Area of Site                                                 P(H)          P(S:H)        P(T:S)      V(D:T)           R(LoL)           Assessment
                                                  Likelihood
                                                                                      -6                                                          -8
                        Area Ia                 Barely Credible                  10              1.0          0.1          0.7           7 x 10               Acceptable

     A
                                                                                      -4                                                          -6
                        Area Ib                       Unlikely                   10              1.0          0.1          0.7           7 x 10               Acceptable


         2.                                                                           -4                                                          -6
    B                   Area II                       Unlikely                   10              1.0          0.1          0.7           7 x 10               Acceptable

                                                                                   -6                                                           -8
                    Overall Site –            Barely Credible to               10 to                                                   7 x 10 to
     C                          3                                                  -5            1.0          0.1          0.7                 -7             Acceptable
                     long term                      Rare                        10                                                      7 x 10

Note:- 1. Refer Appendix B of “Practice Note Guidelines for Landslides Risk Management (2007)”.
              2. Assumes all cuts supported by engineer designed retaining walls.
              3. Assumes it’s addressed by landscaping and control of drainage and overland flow.


TABLE 5               RISK CRITERIA
                Situation                      Suggested Tolerable Loss of Life Risk                                  Suggested Acceptable Loss of Life
                                                  limit for the person most at risk                                   Risk limit for the person most at risk
         Existing Slope                                               10-4 / annum                                                       10-5 / annum
     Existing Development                                             10-4 / annum                                                       10-5 / annum
    New Constructed Slope                                             10-5 /annum                                                        10-6 /annum
      New Development                                                 10-5 /annum                                                        10-6 /annum
      Existing Landslide                                              10-5 /annum                                                        10-6 /annum
Notes:
 “Existing Slopes” in this context are slopes that are not part of a recognizable landslide and have demonstrated non-failure performance over at least several seasons or
   events of extended adverse weather, usually being a period of at least 10 to 20 years.
 “Existing Development” includes existing structures, and slopes that have been modified by cut and fill, that are not located on or part of a recognizable landslide and have
   demonstrated non-failure performance over at least several seasons or events of extended adverse weather, usually being a period of at least 10 to 20 years.
 “New Constructed Slope” includes any change to existing slopes by cut or fill or changes to existing slopes by new stabilisation works (including replacement of existing
   retaining walls or replacement of existing stabilisation measures, such as rock bolts or catch fences).
 “New Development” includes any new structure or change to an existing slope or structure. Where changes to an existing structure or slope result in any cut or fill of less
   than 1.0m vertical height from the toe to the crest and this change does not increase the risk, then the Existing Slope / Existing Structure criterion may be adopted. Where
   changes to an existing structure do not increase the building footprint or do not result in an overall change in footing loads, then the Existing Development criterion may be
   adopted.
 “Existing Landslides” have been considered likely to require remedial works and hence would become a New Constructed Slope and require the lower risk. Even where
   remedial works are not required per se, it would be reasonable expectation of the public for a known landslide to be assessed to the lower risk category as a matter of
   “public safety”
 Acceptable risks are usually considered to be one order of magnitude lower than the Tolerable Risks.
 It is important to distinguish between “acceptable risks” and “tolerable risks”.
 Tolerable Risks are risks within a range that society can live with so as to secure certain benefits. It is a range of risk regarded as non-negligible and needing to be kept
   under review and reduced further if practicable.
 Acceptable Risks are risks which everyone affected is prepared to accept. Action to further reduce such risk is usually not required unless reasonably practicable measures
   are available at low cost in terms of money, time and effort.


     5.8 Risk Summary
A summary of the results of the risk assessment for the existing site condition as detailed in
Sections 5.6 and 5.7 are as follows:-

               Risk to Property - This is outlined in Table 3 and provided the recommendations of this
                report are followed, then the risk of any slope stability occurring on the site has been
                assessed as Very Low or Low.
               Risk to Persons – This is outlined in Table 4 and based on that assessment, the risk to
                persons from the identified hazards was assessed as Acceptable.

We also recommend that once a retention design has been completed, it be reviewed by
Soil Surveys Engineering to ensure compliance with this report and that no additional
stability issues have been created.