Geotechnical Investigation Report

J001369-001-R-Rev0                                                                                            August 2021


5.6    Existing Structures
The existing residence comprised a two-storey brick dwelling on a levelled building pad with an associated
concrete driveway and footpath. It is anticipated that cut and fill earthworks were required for construction of
the existing dwelling. The structures and ground conditions did not show any signs of instability. Tenants on
site further advised that no cracking or major issues have been observed within the existing dwelling.
A timber sleeper retaining wall of about 0.8 m height extends across part of the rear of the site. A brick
retaining wall of about 1.2 m to 1.5 m height extends along the along the northern boundary of the site. The
adjacent property is situated on the high side of the existing brick retaining wall.

6.0     ASSESSMENT OF LAND STABILITY
6.1    Existing Conditions
The Noosa Planning Scheme 2020 includes a landslide hazard overlay map. The overlay map indicates that
the site is within a moderate landslide hazard area. Image 3 below presents an extract of the overlay map.



                                                                                            Lot boundary




Image 3: Extract from Noosa Shire Council landslide hazard overlay mapping.

6.2    Stability Risk Assessment
A qualitative slope stability risk assessment for this project has been carried out following the Australian
Geomechanics Society (AGS) Guidelines for Landslide Risk Management (March 2007), refer Table 2. The
risk assessment relates to property. Relative levels of risk and their implications are given in Table 1 below
and the qualitative terminology (i.e. likelihood and consequence definitions) for use in assessing risk to
property are attached in Appendix B.
Table 1: Stability Risk Levels.
         Risk Level                                                 Example Implications(1)

              VERY HIGH           Unacceptable without treatment. Extensive detailed investigation and research, planning
VH                                and implementation of treatment options essential to reduce risk to Low; may be too
              RISK
                                  expensive and not practical. Work likely to cost more than value of property.
                                  Unacceptable without treatment. Detailed investigation, planning and implementation of
H             HIGH RISK           treatment options required to reduce risk to Low. Work would cost a substantial sum in
                                  relation to the value of the property.
              MODERATE            May be tolerated in certain circumstances (subject to regulators’ approval) but requires
M                                 investigation, planning and implementation of treatment options to reduce risk to Low.
              RISK
                                  Treatment options to reduce to Low risk should be implemented as soon as practicable.
L             LOW RISK            Usually acceptable to regulators. Where treatment has been required to reduce the risk to
                                  this level, ongoing maintenance required.
              VERY LOW
VL                                Acceptable. Manage by normal slope maintenance procedures.
              RISK

Note:
1) The implications for a particular situation are to be determined by all parties to the risk assessment and may depend on
the nature of the property at risk; these are only given as a general guide.




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