slope stability

Integra Partnerships                                                                            22340-001-Rev0
                                                                                             14 September 2022

3.0        RECOMMENDATIONS
3.1       Site Layout and Development Limitations
Should any revisions be made to the extent of the proposed duplexes described in Section 1.1, Tectonic must
review these prior to construction to assess if there are any impacts on our recommendations.

No earthworks details were available at the time of reporting; however, provided drawings indicate that cut
and fill earthworks less than 1.0 m height will be required. Should proposed cuts/fills exceed these quantities,
Tectonic should assess the impacts on slope stability before construction.

3.2       Earthworks
3.2.1         Site Preparation and Trafficability
In construction areas, any relict construction elements, vegetation, tree stumps and large roots should be
stripped and ‘grubbed out’. Any organic rich topsoil or ‘uncontrolled’ fill should also be stripped and removed
from site, based on the boreholes, depths should generally range up to about 0.4 m depth. 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. Where slab on ground
construction is proposed, the 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 vibrating plate).

Care must be taken with the use of vibratory equipment to ensure that there are no adverse impacts on
surrounding structures and underground services. The impacts from ground vibration must be closely
monitored and managed during construction. It would be prudent to conduct a dilapidation survey of
neighbouring structures prior to commencement of construction.

3.2.2          Filling
The existing sandy soils (excluding topsoil) 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 minimum 4 tonne vibrating smooth drum roller or vibrating plate) to achieve required
compaction.

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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