Reference Documents

                                          PROPOSED SUBDIVISION
                                          41 TALLOWWOOD PLACE, BLACK MOUNTAIN



                                                                                         Topsoil
                  Topsoil
                                                                                   Colluvium/Landslide Debris
               Residual Soil



          XW Material/Phyllite




                                                                                                       Fissured/Slickensided Surfaces



            Text Figure 10: Subsurface conditions in test pits TP3 (LHS) and TP2 (RHS)


            4.5         Geotechnical Laboratory Test Results
            Laboratory testing on a sample recovered from test pit TP3 between 0.4 m and 0.7 m BGL, indicates that the
            sample was a clayey silt of high liquid limit, tending to a high plasticity silty clay. It should be noted that, due
            to the high silt and clay content of the soils, the materials are expected to be susceptible to strength loss,
            particularly if they become wet.

            4.6         Groundwater
            No signs of groundwater seepage at the surface (‘springs’) were observed during our walk-over around the
            proposed development area. Groundwater was not encountered in the test pits at the time of investigation;
            however, increased moisture conditions (moist to wet soils) were encountered in the deep colluvium profile in
            test pit TP2. The soils within the test pits across the proposed new building area were dry to moist.
            Groundwater conditions are expected to be reflective of prevailing weather conditions and seepage may
            develop, particularly at depth following periods of prolonged or heavy rainfall.

            4.7         Surface Drainage
            Natural surface drainage follows the ground surface gradients from the proposed development area and
            broader site to the north, ultimately into a creek beyond the site boundaries. Generally, surface water is
            expected to drain well from the site considering the positive gradients and low permeability of the clayey
            soils; however, poorer drainage conditions are anticipated on level areas.

            No signs of significant erosion were observed around the proposed development area at the time of the
            assessment; however, rill erosion was observed around the existing residence in areas where concentrated
            stormwater flows appear to develop.

            4.8         Vegetation
            The proposed new building area was primarily covered by grass. Areas around the existing residence
            comprised landscaped gardens and maintained grass with scattered trees. Relatively dense bushland
            occupied most of the western part of the site and traced the northern boundary. Some of the trees on
            steeper slopes and within the drainage lines were noted to be tilting/leaning with ‘J’ shaped curves which
            can be a sign of previous instability. Generally, the trees around the proposed new building area were
            relatively straight, exhibiting no obvious signs which would indicate global slope instability.




             22 May 2023
             Report No. 23099-001-Rev0                                8

Document Set ID: 22826802
Version: 1, Version Date: 23/02/2024