slope stability · MCU22/0172

Integra Partnerships                                                                                     22339-001-Rev0
                                                                                                      13 September 2022

Table 2 is our qualitative assessment of landslide risk for the development site. A summary of qualitative
terminology for use in assessing risk to property is attached (taken from AGS 2007).
Table 2: Details of Qualitative Risk Assessment for Property (AGS 2007)

                                                                   Assessed
 Hazard                             Likelihood   Consequence         Risk     Comments


                                                                              Given the low to moderate natural gradients through
                                                                              the proposed building area it is considered Unlikely
 1: Failure through very loose to                                             that a landslip would develop in these materials,
loose natural sands above the        Unlikely      Medium            Low      subject to implementation of the recommendations in
foundation depth                                                              Section 4. It is assessed that there could be a
                                                                              potential Medium impact from such instability so the
                                                                              resultant risk would be Low as per AGS 2007.


                                                                              The likelihood of a deep failure through the medium
                                                                              dense (or denser) natural sand below the proposed
                                                                              foundation depth is assessed as Rare due to the lack of
 2: Deep failure through the
                                                                              precedence of such movements locally, no signs of any
medium dense (or denser) sands        Rare          Major            Low
                                                                              existing slope instability and apparent lack of
below the foundation depth
                                                                              groundwater. Although the consequence of such a
                                                                              failure could be Major, the resultant risk is Low as per
                                                                              AGS 2007.


The potential impacts on slope stability of the development components have been assessed, and the
measures recommended below in Section 4 have been designed to mitigate those impacts.



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
Should any revisions be made to the extent of the proposed residences described in Section 1.1, Tectonic
must review these prior to construction to assess if there are any impacts on slope stability.
No earthworks details were available at the time of reporting; however, provided drawings indicate that
excavations up to 2.5 m depth and fill earthworks less than 1.0 m height will be required. Should proposed
cuts/fills exceed these quantities, Tectonic must assess the impacts on slope stability before construction.

4.2     Earthworks
4.2.1        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 should also be stripped and removed from site, based
on the boreholes, depths should generally range up to about 0.2 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 (e.g. existing NC sewer infrastructure along the front
boundary). The impacts from ground vibration must be closely monitored and managed during construction.




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