Attachment C - Geotechnical investigation

                                                                                                51 640 311 842
                                                                                                    CONTACT
                                                                                   [email protected]
                                                                                            arcosgroup.com.au
                                                                                                      OFFICES
                                                                        Sunshine Coast | Brisbane | Gold Coast




8.0 Geotechnical Recommendations
The following sections details specific geotechnical constraints or recommendations in
addition to general hillside construction notes.

8.1 Site Preparation and Earthworks
The following comments are provided in relation to site preparation for earthworks.
•   No fill at this site is to be placed unless supported by an engineer designed and certified
    retaining structure
•   Areas where fill is proposed should be stripped of uncontrolled fill, soft, overly wet,
    foreign, or otherwise deemed unsuitable material (material that is potentially
    compressible) down to a relatively stiff dry base ensuring no organics material is present.
•   Stripped areas must be inspected by the geotechnical testing authority (GTA) to ensure
    no soft spots or loose zones are present. This should be done with the use of a loaded
    body truck or 12 tonne roller as a minimum. Areas showing signs of movement under the
    action of the testing equipment should be either over excavated and replaced with select
    fill or conditioned onsite through tyning, blending or other suitable methods.
•   Areas sloping in excess of approximately 1 vertical unit to 10 horizontal units (1V:10H),
    the surface will need to be benched at a minimum vertical bench height of 0.3 m to enable
    keying in of the new fill and existing soil. The benches will also need to be shaped
    adequately to promote drainage.
•   Edge batters should be formed by over filling an area and ‘trimming’ back to the desired
    profile.
•   Although no standard exists for the moisture content of soils, it is recommended that the
    site soils be placed at or near optimum moisture content (OMC) for general earthworks
    operations. This increases efficiency during earthworks operations. A range of +/- 2% of
    OMC is recommend for general earthworks.
•    Where site soils are proposed for use as fill in other areas, won material will need to have
    a maximum particle size of 75 mm or be observed to break down under the energy of
    compactive equipment.
•   Fill materials should be placed in relatively horizontal layers with a maximum placement
    thickness of 200 mm. The materials should be compacted to a minimum dry density ratio
    of 98% relative to Standard compactive effort.
•   Highly plastic natural clays are very sensitive to the presence or lack of moisture and
    therefore care should be used to place the material within the range nominated and to a
    maximum dry density of 102% relative to Standard compactive effort. Where this does
    not happen, the material could readily swell, soften, or be subject to significant
    trafficability issues.
•   Earthworks quality testing will be required on this site. The GTA will need to provide
    supervision in accordance with AS3798 and undertake field density tests to monitor the
    actual dry density and moisture content of placed materials.

09 Feb 2021                                                        Proposed Residential Dwelling