Geotechnical Investigation Report

J001369-001-R-Rev0                                                                                          August 2021


Table 2: Qualitative Risk Assessment for Property (Based on AGS 2007)
                                                              Assessed
           Hazard           Likelihood   Consequence                                        Comments
                                                                Risk
                                                                          The likelihood of shallow failure is assessed
 Shallow failure through
                                                                          as Unlikely. The consequence is considered
  loose fill and natural
                             Unlikely       Medium              Low       Medium, if the proposed development is
 aeolian soils above the
                                                                          founded as per the recommendations in this
    foundation depth
                                                                          report. The resultant risk is Low.
                                                                          The likelihood of a deep failure through the
Deep failure through the                                                  natural aeolian soil is assessed as Rare due
  dense (or denser)                                                       to historically low prevalence of instability in
 natural aeolian soils        Rare           Major              Low       this geological formation and no signs of
 below the foundation                                                     slope instability. Although the consequence
         depth                                                            of such a failure would be Major, the
                                                                          resultant risk is Low.

Based on the available information and the results of our investigation, it is our opinion that there is a Low
Risk of slope instability for the proposed development, subject to implementation of the recommendations in
this report, assessed in accordance with the AGS guidelines (March 2007).

7.0        DEVELOPMENT IMPACTS AND MITIGATION MEASURES
The potential impacts of the proposed development on slope stability have been considered, and the
measures recommended below have been designed to mitigate potential impacts. Building development
should follow normal slope maintenance procedures and the document ‘Guidelines for Hillside Construction’,
which is attached in Appendix C.

7.1       Site Preparation and Trafficability
Site preparation across the development footprint should include the following:

      ▪    Remove vegetation and ‘grub out’ stumps, large roots and root balls
      ▪    Remove any topsoil and uncontrolled fil. Topsoil was encountered between 0.1 and 0.18 m BGL,
           however deeper pockets may exist across the site. It is noted that dense vegetation was observed in
           the south-west and north-east portion of the site, where deeper organic materials may be present.
The base of the excavation is anticipated to comprise dense sands, which may become disturbed/loose at
the surface from excavation/construction traffic. Compaction of such loose sands may be required, using a
smooth-drum roller (4 tonne). Vibration and the application of water may be required. However vibration
impacts on adjacent sites must be assessed.
Allowance should be made for the placement of a 150 mm thick layer of aggregate across the base to form
an even and stable working platform, or on access/laydown areas.
The site must be maintained to shed water and prevent ponding during the construction phase. Erosion and
sediment control measures must be put in place during construction.
It would be prudent to carry out a dilapidation survey of adjacent structures and sites prior to site works.

7.2       Filling and Compaction
It is anticipated that filling will be minimal and will only be required to form finished surface levels or on
removal and replacement of unsuitable material.
Where filling is undertaken, the following measures should be adopted:

      ▪    Fill should be compacted at moisture contents within the range of ±2% of optimum moisture content
           for Standard Compaction.
      ▪    Confirmatory compaction testing must be carried out at regular intervals. Guidance on testing
           frequency is provided in AS 3798-2007 Table 8.1.
      ▪    Fill should have a maximum particle size of 100 mm.




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