Geotechnical Stability Report · OPW24/0017

GMW Projects Pty Ltd                                                                           24008-001-Rev0
                                                                                               31 January 2024

4.2       Earthworks
No earthworks details were available at the time of reporting; however, the provided plans suggest that cut
and fill earthworks in the order of about 1 m deep and 1.5 m high may be required, most of which will be
supported by retaining structures. Should proposed earthworks exceed these limits, Tectonic must assess
the impacts on slope stability before construction.

4.2.1         Site Preparation and Trafficability
In construction areas, any relict construction elements (other than those approved by the structural RPEQ),
vegetation, tree stumps and large roots should be stripped and ‘grubbed out’. Any organic rich topsoil
should also be stripped and removed from site. Organic topsoils and garden soils must not be re-used as
structural fill; however, small volumes may be retained on site for later use across landscaping areas, if
required.

The natural subgrade following stripping will likely be in a loose condition. Should slab on ground
construction be proposed (e.g. new driveway, concrete pathways etc.) the ground surface should be
compacted by several passes of a vibrating plate compactor or small smooth drum roller (or similar) in
conjunction with the surface application of ample water.
Care must be taken with the use of any vibratory equipment to ensure that there are no adverse impacts on
surrounding structures and underground services (e.g. existing Noosa Council infrastructure along the site
boundaries). The impacts from ground vibration must be closely monitored and managed during
construction. Where significant vibrations are possible, it would be prudent to conduct a dilapidation survey
of neighbouring structures prior to commencement of construction.

4.2.2          Filling
The natural sandy soils (excluding topsoil and garden soils) may be reused as structural fill, subject to
appropriate moisture adjustment. It should be noted that compaction of such relatively ‘clean’ sands as
structural fill requires the addition of substantial volumes of water (‘flooding’) combined with the use of
vibratory compaction equipment (typically a smooth drum roller or vibrating plate). Where significant
vibrations likely to damage adjacent property or infrastructure are generated, the placement of fill in thinner
layers and the use of static compaction equipment should be considered.

Should importation of fill be required, it is recommended that such fill should comply with the following:

          Minimum CBR of 10%
          Maximum plasticity index of 15%
          Shrink-swell index ≤ 1%
          Maximum particle size of 100 mm

Any fill should be compacted at moisture contents within the range of ±2% of optimum moisture content for
Standard Compaction. Select fill should have a maximum particle size of 100 mm for an uncompacted layer
thickness of 200 mm and shall be compacted by repeated rolling with a small compactor to achieve a dry
density ratio of at least 95% of the Standard Maximum Dry Density for cohesive soils, or 70% Dry Density
Index for any imported cohesionless soils.

Confirmatory compaction testing should be carried out at regular intervals. A minimum of two tests per
vertical lift is recommended where structural fill heights are to exceed 300 mm. Further details for control
and testing of fill are given in Australian Standard AS 3798-2007 Guidelines on Earthworks for Commercial
and Residential Developments.

Fill embankment edges must be over-filled by 0.5 m (horizontally) and then trimmed back to well compacted
material.




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