Slope Stability Report 26-5-2019 OPW19-0193

TRUBUILT
SLOPE RISK ASSESSMENT REPORT



3.         ASSESSMENT OF LAND STABILITY

3.1        Existing Conditions

An assessment was made for tell-tale signs of slope instability over the site; the features identified comprised
the following:

      •   Colluvial soil as a mantle on the slope;
      •   Tension cracking and creek instability in gullies on surrounding slopes;
      •   Shallow slumping in cut batter slope.

The impact of observed instability and other slope factors is discussed further in Sections 3.2 and 3.4.


3.2        Components of Development and Potential Geotechnical Impact

The proposed development is likely to have a geotechnical impact on the site, the manner and extent of this
impact is dependent on the location and manner of the component of development. A summary of potential
geotechnical impacts of various components of the development and the potential instability mechanisms is
summarised in Table 1.

Table 1 - Development components with geotechnical impact and potential instability mechanism
      Development Component               Potential Geotechnical Impact        Potential Instability Mechanism
       Construction of house                  Loading of the slope                    Global instability
                                         Steepening of slope, exposure of
              Cut batters                                                      Wedge failure, translational slide
                                              internal rock defects
                                                                                  Global instability, shallow
              Fill batters                     Loading of the slopes
                                                                                          slumping
  Wastewater irrigation area and         Saturation of steeper sections of       Creep flow and translational
      stormwater disposal                           the slope                               sliding


3.3        Slope Stability Risk Assessment

The slope stability assessment was completed using the requirements if the Australian Geomechanics Society
“Practice Note Guidelines for Landslide Risk Management 2007” (Walker et al 2007). This framework provides
the requirements for assessments and the allocation of risk to landslide prone and steep land areas.

The site has been identified by the council as being in either a steep land and/or landslide prone area and
consequently the impact of the proposed development on the stability of the site needs to be considered.

The potential hazards identified in section 3.2 or that would need to be considered for this type of
development would comprise the following:

      •   Global failure – complete failure of the slope and the building;



LEONTAKIANAKOS-R-001                                 Page 8                                             26 May 2019