Slope Stability Assessment

Jane & Cameron Blake                                                                           22178-001-Rev0
                                                                                                  26 May 2022

3.2.1 Effluent Disposal
No effluent disposal information for the proposed new residence had been provided at the time of reporting,
however the effluent disposal area should be located so that it is setback at least 15 m from the proposed
dwelling and run-off does not flow towards the development area, driveway or cuttings/embankments (i.e.
wastewater application areas should either be to the side(s) or down slope). The existing effluent
disposal/septic system should be inspected by a suitably qualified person to confirm it is performing
adequately and updated accordingly (if required).
It is recommended that diversion drainage be installed upslope of the irrigation area to avoid surface water
infiltrating into shallow trenches the land application area be revegetated as soon as possible. Vegetation
should include native species which are used for stabilisation of steep slopes and suitable for wet soils with
high nutrient loads (e.g. Lomandra).

The on-site effluent disposal system must be located a suitable distance away from any watercourse,
dwellings and recreation areas. Setback distances are subject to the level of treatment proposed and shall
be in accordance with Local and State Government requirements.

4.0        RECOMMENDATIONS
General recommendations to help maintain the stability of the site are given in the document Some
Guidelines for Hillside Construction, which is attached.

4.1       Site Layout and Development Limitations
The planned extents of the proposed development shown in Text Figure 2 are acceptable from a slope
stability viewpoint. Should any revisions be made to the proposed extent of the development, Tectonic must
review these prior to construction to assess if there are any impacts on slope stability.

To achieve a Low Risk of instability, the following is recommended:

          Tectonic must review a suitable soil test report, development plans and earthworks drawings
           (including the proposed driveway alignment), with this report revised prior to construction.
          All retaining walls exceeding 1 m high and/or subject to surcharge loads must be RPEQ designed
           and certified, which must include an assessment of global and internal stability.
          Fill heights shall be limited to no more than 1 m on slopes exceeding 10°, unless assessed and
           approved by a geotechnical RPEQ, and fully supported by an engineer designed and certified
           retaining wall.
          Design and construction of footings shall be undertaken in accordance with Section 4.3.
          Formalised drainage should be constructed to ensure all stormwater is directed away from
           structures and footings.

4.2       Earthworks
Cut and fill earthworks for the proposed central development (horse arena, shed etc.) are anticipated to be
relatively minor (i.e. less than 1 m depth/height). Based on provided sections it is anticipated that
excavations for the proposed new residence and surrounding ancillary structures will range up to about 4 m
deep, with filling likely to be up to about 1.5 m high to form finished levels and for the grassed terrace. No
details for the proposed access driveway has been provided; however, it is envisaged that cut and fill
earthworks in the order of 1 m depth/height will be required, depending on the desired alignment.

4.2.1 Site Preparation and Trafficability
Any organic rich topsoil, firm/loose (or weaker) soils and overly wet materials must be stripped and removed
from any pavement or at grade construction areas. Topsoil materials must not be used in structural fill;
however, may be placed across landscaping areas. It is recommended that any at grade building/pavement
subgrades be proof rolled using a minimum 4 tonne pad foot roller to identify any ‘soft spots’ in the presence
of a suitably qualified and experienced civil/geotechnical engineer. Any such soft spots should be excavated
and replaced with select fill material, constructed as recommended in Section 4.2.3.




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