Slope Stability Report

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5.0 Walkover Assessment
Geotechnical comments are based on the factual findings of the investigation, best practice,
local experience, published correlations; however, are fundamentally founded in opinion and
this should be considered.


An experienced geotechnical engineer undertook the walkover assessment on                          May 2021.
Overall the lot falls away to the south-east, with small retaining walls used to allow for a flat
house pad. The neighbouring walkway shows t             grade of the land without retaining walls
where a slope of up to 10° is present. No obvious signs of disturbed ground, tension cracks or
hummocks were noted during the assessment.

6.0 AGS Assessment
Landslides are caused where a soil or rock mass has a decrease in strength, usually attributed
to groundwater, resulting in the material not being able to maintain its own self-weight
resulting in a slope failure.


The Australian Geomechanics Society (AGS) developed a set of tools and procedures for
assessing the stability of a slope. The tools and procedures presented with the AGS
documentation form the basis of the assessment undertaken herein and their documentation
is attached for reference.


The guidelines also identify that the regulator typically sets the standard for levels of tolerable
risk. AGS defines tolerable risk as “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”.

The guides suggest that areas of moderate or greater risk should not be developed unless a
rigorous remediation plan be implemented to reduce the area to a level of Acceptable Risk .
AGS defines acceptable risk as “risk 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”.

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.

12 May 2021                                                         Propsoed Residential Extensions