210408 - 72 Podargus Parade, PEREGIAN BEACH - 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 06 Oct 2021.
As part of the walkover assessment, 'spot' measures were taken of the slope angles and
observations pertaining the any obvious previous slope instability on the allotment and
immediately adjoining areas that were readily accessible at the time of the inspection was
undertaken. The surface levels on the site fall away to the north-east at relatively uniform
grades of approximately 11°. On the downhill neighbouring property, an approximately 1m
high retaining wall and an approximately 33°, 1m wide batter are present running parallel to
the property boundary. No obvious signs of disturbed ground, tension cracks or hummocks
were noted during the walkover assessment. A variety of vegetation ranging from small shrubs
to mature trees were observed. The mature trees were all observed to be typically vertical with
no misshapen or curved trunks. Misshapen or curved trunks are usually good indicators for
previous slope instability. The photographs attached to this report show the conditions of the
site at the time of the inspection and assessment undertaken.

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.”.



12 Oct 2021                                                                       Proposed Extensions