Attachment 3 - Geotechnical Report

LOT 21 (16) PINES ROAD, COOROY                                              EBIS REFERENCE NO: 210417-SU/GEO


Definitions of acceptable and tolerable risks as included in the AGS Practice Note Guidelines
are as follows:

Tolerable Risk: 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 Risk: 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.

The predominant issue at the site is the developments proposed cut/fill earthorks on the
moderate to steep slopes.

An assessment of the risk of slope instability has been carried out for the site, based on the
results of the investigation and experience in similar projects, provided that development of
the site is carried out in accordance with good engineering practice for hillside
developments and the recommendations within this report.

It is considered that the blanket overlay risk rating is reduced by the following site
conditions:

        No evidence of slumping/slip in rock faces in existing cut embankments;
        Relatively shallow soils overlying stable bedrock strata (typically less than 1,000mm);
        No previous known or mapped landslips on or close to site;
        Ground water not evident during site testing and not generally associated with the
         geology and elevation of the site on a ridge line;
        Very little surface water is naturally (or otherwise) directed towards the site as the
         development area is on the crest or summit of a ridge line.

Table 2 – Slope Instability Risk Assessment to Property

         Hazard             Likelihood   Consequence        Assessed Risk                  Comments
                                                             to Property
1.
Shallow slumping,          Possible      Minor          Moderate             Mitigation Measures Required:
rotational or slip in                                   Risk
residual soils above                                                         The likelihood of failure of the
bedrock at house                                                             shallow soils overlying the
site                                                                         weathered rock is possible with a
                                                                             minor consequence.

                                                                             Together      with    measures
                                                                             recommended in this report
                                                                             which includes founding all
                                                                             footings/foundations   into/on
                                                                             sound weathered rock.

                                                                             As per AGS 2007 the resultant risk
                                                                             is low
2.
Failure in rock layer      Barely        Major          Very Low             The consequence of failure is
                           Credible                                          major however the likelihood is
                                                                             barely credible.

                                                                      As per AGS 2007 the resultant risk
                                                                      is very low
Suitable building methods must be adopted with treatment required as outlined following
in this report to provide for acceptable risk levels (very low –low risk).


PROPOSED NEW RESIDENCE                       PAGE 7 OF 10                                       4 March 2022