Geotechnical Investigation Report

6.7 LANDSLIDE RISK ASSESSMENT

Noosa Shire Council mapping indicates that the proposed site is mapped as a ‘moderate hazards area’, as shown in
Figure 3.

 

 

      
  
  

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Based on the results of the ground conditions encountered at the site, two potential failure mechanics can be
considered, these include:
Hazard 1- Small rotational failure through the natural loose sands - volume of failure less than 20m3 (failure will
required an unusual sever triggering event)
Hazard 2 - Large rotational failure through the natural loose sands - volume of failure less than 2000m3 (failure
will required an extreme triggering event)

A qualitative landslip risk assessment was completed for these potential failure mechanisms in general accordance
with Australian Geomechanics (2007) Guideline for Landslip Susceptibility, Hazard and Risk Zoning for Land Use
Planning). The slope risk assessment is summarised in Table 5.

The small and large rotational failures through the loose sands are of very low and low risk, respectively and are
unlikely to impact the property and people who live or spend time in the area, provided the following recommendation
are adhered too:
All temporary and permanent retaining walls and excavations shall be designed in accordance with AS4678, and
stability analysis be carried out by a geotechnical engineering ensuring minimum Factors of Safety (FOS) for
temporary and permanent conditions of 1.3 and 1.5, respectively are achieved.
All foundations of the house to be extended to the medium dense sand, as a minimum.
The development shall adhere to good hill side practice. Examples of good and poor hill side practice for the
construction of residential dwelling on slopes is presented in Appendix D, Practice Note Guidelines for landslide
risk management 2007, from Australian Geomechanics Journal Vo 42, No. 1 dated March 2007.