OPW052025 Report - Part 2

5.               Slope Stability Assessment
5.1              Existing Conditions
NC Landslide Hazard Overlay mapping (Ref. extract in Text Figure 11) indicates that the overall lot
includes areas of Moderate and High susceptibility to landslide. Along the alignment of the future
driveway, and the building area for the proposed house however, a Moderate susceptibility has been
mapped.




    Approx. building area for
                      house




                                                                  Lot boundary



                                Text Figure 11: Extract of NC Landslide Hazard Overlay Mapping

It should be noted that the NC map is a broad-scale indication of potential landslide susceptibility only
and is superseded by this site-specific assessment and analysis. Our observations of surface features
relevant to the slope stability assessment are as follows:
▪      Evidence of slope instability was not observed local to the construction areas, although it is
       acknowledged that the slopes below the driveway and house site (particularly to the north of the
       driveway) would be sensitive to adverse conditions (e.g. uncontrolled surface water, surcharging by
       filling, etc.).
▪      In situ residual soils, XW materials and weathered basalt/phyllite were encountered in the test pits at
       shallow depth and investigation locations near the construction areas.
▪      No colluvium was logged at the investigation locations and was not observed otherwise in proximity
       to the proposed house site or driveway alignment. Localised slopewash was logged in test pit TP3,
       however was a veneer (0.25 m thick) and represented a very localised system. Colluvium deposits
       were noted in small cuttings and exposed areas downslope and to the north of the proposed
       driveway and are likely to represent former landslide activity (Ref. Section 4.1). These areas were
       >100 m from the driveway, however.




Geotechnical Investigation & Slope Stability Assessment
9 April 2025 | 25050-001-Rev0                                                                               13