Slope Stability Report 26-5-2019 OPW19-0193

TRUBUILT
SLOPE RISK ASSESSMENT REPORT



Further guidance on earthworks is contained in Australian Geoguide LR8 Hillside Construction.


4.4        Batter Slopes for Cut and Fill

The proposed development includes the requirements to modify levels on the site through earthworks. Note
the performance of slopes is dependent on materials, type of material, slope angle, loading and can change
with time. The following recommendations are made with respect to retaining walls, and/or batter slopes in
cut or fill:

      •   Fill slopes should be constructed using compacted material that is initially over constructed and the
          cut back to the final position, fill slopes should generally be no steeper than 1(V):1.5(H), fill slopes
          greater than 5m in total height should be benched to reduce the overall slope length. Modifications
          to this recommended batter angle may be approved following inspection and/or design by a suitably
          qualified geotechnical engineer;
      •   Cut slopes in soil should generally be no steeper than 1(V):1.5(H) and slopes greater than 5m in total
          height should be benched to reduce the overall slope length. Modifications to this recommended
          batter angle may be approved following inspection and/or design by a suitably qualified geotechnical
          engineer;
      •   Cut slopes in weathered and decomposed rock should generally be no steeper than 1(V):1 (H) and
          slopes greater than 4m in total height should be benched. Note that if the foliation of the rock is sub
          parallel to the slope, the rock should be cut to the prevailing foliation angle for greater stability.
          Modifications to this recommended batter angle may be approved following inspection and/or design
          by a suitably qualified geotechnical engineer;
      •   Unless crest drainage will be maintained or comprise self-flushing, trowelled concrete lined drains
          then it is recommended that other methods for the control of surface water on slopes be utilised;
      •   Examples of suitable crest and slope drainage would include grass lined drains that are regularly
          mowed with the surrounding grass, drains lined with Concrete Canvas™, trowelled concrete, stone
          pitching or wire mattress revetments, paving, concrete or steel drainage channels, or some specialist
          geotextile products. Note that it is recommended that drain liners protect the underlying soil from
          erosion and include stilling or dissipating features to slow the velocity of flow along and at the outfall
          location. The use of timber or natural fibres (hemp, cotton, jute or coir) is not recommended for
          permanent drainage features,
      •   Where crest and slope drainage are formed from fill materials, fill materials should use non-dispersive
          soil that is compacted and formed to a suitable batter slope. Drains formed from cut/fill soil should
          have battered sides, be appropriately lined and be of suitable size with regards to the catchment area
          and characteristics, design storm, method of lining, maintenance and/or effect if the drain overflows;
      •   The cut and fill batter slopes in soil and weathered or decomposed rock should be protected from the
          effects of surface water flow through planting with grass, groundcover, shrubs and small trees.
          Generally, plants should have fibrous root and allow undergrowth. Large trees with shallow root
          systems, conifers and plants that prevent the development of undergrowth should be avoided;
      •   Trees and other plants with invasive root systems should not be allowed to grow on cut slopes in rock
          as they can result in root wedging and degradation of the slope;




LEONTAKIANAKOS-R-001                                 Page 14                                             26 May 2019