Appendix E - Geotechnical Report

                                       PROPOSED RECONFIGURATION OF A LOT
                                       216 BLACK MOUNTAIN ROAD, BLACK MOUNTAIN

6.1.3             Quantitative Stability Assessment
In order to calculate the factor of safety (FOS) against slope instability for a residence situated within the
nominated building envelope on proposed Lot 2, numerical analysis has been conducted using the Slope/W
computer program adopting subsurface conditions based on the site investigation. The subsurface profile
described in Section 5.2 has been used in the analysis, together with the ground surface profile from the
slope crest down to the bed of the gully across the proposed building envelope.

Results of the numerical slope stability analysis are provided below.
                                                  1.5
                                                                                                                Name: EW Materi al
                                                                                                                Unit Weight: 18 kN/m ³
                                                                                                                Cohesion': 4 kPa
                                                                                                                Phi': 25 °




                              20 kPa surcharge to represent house/fil l pad




     Name: Residual Soil
     Unit Weight: 19 kN/m ³
     Cohesion': 5 kPa                                                         Name: Weathered Phyl li te Rock
     Phi': 27 °                                                               Unit Weight: 27 kN/m ³
                                                                              Cohesion': 15 kPa
                                                                              Phi': 32 °




Text Figure 8: Extract from SlopeW Modelling

The key points from our analysis are summarised as follows:

          Unit weight and shear strength parameters adopted for the soil and weathered rock strata were
           taken mainly from the lower to mid-range of values recommended for similar materials in Appendix D
           of Australian Standard AS4678-2002 ‘Earth Retaining Structures’.
          Analysis was undertaken for specified slip entry and exit zones, with minimum FOS values of 1.5
           being recorded, assuming the groundwater table is situated at the soil/rock interface (it should be
           noted that groundwater was not encountered in the test pits), and a 20 kPa surcharge area (to
           represent up to 1 m of fill).
This therefore, satisfies the requirement for hillside developments in the NC criteria for construction on steep
land, and the general industry minimum FOS.

Our analysis indicates that the proposed development will achieve at least the required minimum FOS.
Subject to implementation of the recommendations made in Section 7 during development works, there will
be a Low Risk of slope instability affecting the proposed development.




19 June 2018
Report No. 17427-001-Rev0                                                                 8