Slope Stability Report - Site 3

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reduce such risk is usually not required unless reasonably practicable measures are available at low
cost in terms of money, time and effort.”.

AGS suggest that regulators generally accept risk levels of “low” or lower as a level of
acceptable risk.

AGS prepared a semi-quantitative assessment tool for determining the level of risk for a site.
The tool separates the potential hazards for a site, from a stability context, and rates them with
a level of risk frequency. The multiplication of these individual risk frequency summates as the
risk frequency rating which is then measured against the levels of risk nominated by AGS.


The results of this analysis are shown in Table 1.


Table 1: Results of AGS Qualitative Risk Assessment
                Hazard                         Likelihood      Consequence                Risk Level
             Global Failure                  Barely Credible   Catastrophic                    Low
    Shallow slumping of surface soils             Likely          Minor                    Moderate




Based on the results of the AGS assessment, the perceived risk based on the conditions
encountered and information available at the time of the assessment is “low”.

7.0 Hillside Construction
The following works should be implemented in additional to other items highlighted within
this document. These points are considered to be typical good hillside construction practice
as explained in attached documentation:

•     Foundations for lightly loaded or non-liveable structures should be founded on and keyed
      into stiff (or stronger) natural clays; Heavy structures should be supported on either piles
      founded into weathered sandstone or high level footings founding into the same material.
•     Where slopes are not supported by an engineer designed support system, natural slopes
      within or near building envelope or movement sensitive areas should be no steeper than
      2H:1V.
•     Building platform fill should be limited to a maximum height of 1 m. The filling should be
      step keyed into the natural slope and battered no steeper than 3H:1V unless an engineer
      designed retention system is in place.
•     Unsupported cuts steeper than 2.5H:1V will require engineer designed retention systems.
•     All stormwater and surface water is to be discharged by an approved stormwater drainage
      system. The use of subsurface drainage systems are not suitable unless greater than 50
      m downslope from the envelope at this site.
•     Plumbing and services must also not be allowed to leak and regular maintenance and
      inspections should be undertaken.

30 Nov 2020                                                              Geotechnical Investigation