MCU25 0087 - Reference Document - Geotech assessment report (As Published) · MCU25/0087

        5.              Slope Stability Assessment
        5.1             Existing Conditions
        The Noosa Planning Scheme 2020 includes a landslide hazard overlay map (Ref. extract in Text Figure 8)
        which indicates that the eastern edge of the site, and steeper dune face to the east, have been mapped
        as Moderate and High Hazard areas, respectively.




                                                       Subject site




                                  Text Figure 8: Extract from NC landslide hazard overlay mapping

        It should be noted that the NC landslide hazard mapping is a broad-scale indication of the potential
        landslide susceptibility and is superseded by this site-specific assessment. The allotment and adjacent
        dune face did not exhibit any visible surface features which would indicate larger scale global slope
        instability during our walk-over. No landslide back scarps, noteworthy groundwater seepage or areas of
        naturally ‘hummocky’ ground were observed. Medium dense sands were encountered at relatively
        shallow depths below surface down the dune face, with the dune standing at around 30° overall.
        Generally, sand dune slopes are close to the ‘limit of equilibrium’ where the surface gradient is about 30°,
        although often lower (26˚ to 28˚) for very loose sands (as were indicated to be present down the dune in
        DCP1 to DCP3 to depths of up to 1.9 m BGL). The limit of equilibrium is the ‘tipping point’ to instability,
        where the factor of safety (FOS) of the slope is approximately 1.0. The FOS of a slope is the balance (ratio)
        between the forces driving instability (e.g. soil weight, groundwater pressure) and the resisting forces (e.g.
        soil friction and cohesion).


        5.2             Stability Assessment
        The risk assessment for this project has been carried out following AGS 2007 Practice Note Guidelines for
        Landslide Risk Management. Relative levels of risk and their implications are given in Table 2 on the
        following page.




        Geotechnical investigation
        19 November 2025 | 25289-001-Rev0                                                                           10
Document Set ID: 24631529
Version: 1, Version Date: 24/03/2026