Reference Document - OPW25 0085 (AS Published)

6.           Geotechnical Recommendations
General recommendations to help maintain the stability of the site are given in the document Some
Guidelines for Hillside Construction, which is attached in Appendix C.


6.1          Site Layout and Geotechnical Constraints
From the conceptual earthworks plans it is anticipated that cut earthworks up to 2 m depth and filling up
to 1 m high will be required for construction of the new road and driveways. Earthworks depths/heights
must not exceed these values unless assessed by a geotechnical RPEQ before construction.
From a geotechnical and slope stability perspective there would not be significant limitations over the
majority of lots in terms of building envelopes. However, to avoid potentially adverse zones, building
areas would be suited to the highest points of the sites and away from the natural drainage lines.
To achieve a Low Risk of instability, the following is recommended:
    For future building works, unretained fill heights on slopes between 10° (18%) and 20° (35%) shall be
     limited to no more than 1.5 m for future residential construction, unless assessed and approved by a
     suitably qualified and experienced geotechnical RPEQ.
    For future building works, no fill should be placed on slopes greater than 20°, unless assessed and
     approved by a suitably qualified and experienced geotechnical RPEQ.
    All retaining walls exceeding 1 m high and/or subject to surcharge loads must be engineer designed
     and certified, which must include an assessment of global and internal stability.
    Design and construction of footings shall be undertaken in accordance with Section 6.3.2.
    Formal drainage should be constructed to ensure all stormwater is directed away from the proposed
     structures and effluent disposal areas.
    Site specific site classification and slope stability assessments must be carried out for each new
     allotment, where required by NC/Private Certifier, which appropriately consider the proposed
     residential construction plans prior to building works commencing.
Final Operational Works earthworks design drawings should be assessed by Tectonic prior to
construction.


6.2          Earthworks
6.2.1        Site Preparation and Trafficability
In construction areas, following clearing of vegetation, tree stumps and large roots must be ‘grubbed
out’ and any organic rich topsoil and/or any unsuitable materials (e.g. firm/loose or water softened
materials) must be stripped and removed. Topsoil materials must not be used in structural fill; however,
may be placed to shallow depths (<0.5 m) across landscaping or effluent disposal areas (if required).
It is recommended that, following removal of unsuitable materials, all building/pavement subgrades
should be proof rolled using a minimum 4 tonne roller in the presence of a civil/geotechnical RPEQ to
identify any ‘soft spots’. Materials in any such soft spots should be excavated and replaced with select fill
material, constructed as recommended in Section 6.2.4.




Geo-Environmental Investigation for Proposed Subdivision
7 February 2025 | 24386-001-Rev0                                                                           16