Appendix4-SlopeStabilityAssessment · MCU18/0135

Structures Engineering Design                                                                                18197-001-Rev0
                                                                                                               6 August 2018

 Table 2: Details of Qualitative Risk Assessment for Property (AGS 2007)

                                                                 Assessed
 Hazard                             Likelihood   Consequence
                                                                   Risk
                                                                            Comments

                                                                            Given the gentle natural gradients (i.e. (5˚ to 7˚)
                                                                            through the building area and moderate grades
                                                                            downslope (~12˚) it is considered Unlikely that a
 1: Failure through very                                                    landslip would develop in these materials, subject to
loose/loose natural soils above      Unlikely      Medium             Low   implementation of the recommendations in
the foundation depth                                                        Section 4 including footings founded below the very
                                                                            loos/loose materials. Given a potential Medium
                                                                            impact from such instability the resultant risk would
                                                                            be Low as per AGS 2007.

                                                                            The likelihood of a deep failure through the medium
                                                                            dense natural sand is assessed as Rare due to the
 2: Deep failure through the                                                gentle to moderate overall ground slopes, relatively
natural soil below the foundation     Rare          Major             Low   light building loads, and no signs of any existing slope
depth                                                                       instability and lack of groundwater. Although the
                                                                            consequence of such a failure would 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
The proposed location of the residence shown on the provided architectural drawings is acceptable from a
geotechnical viewpoint.

4.2    Earthworks
We understand that only minor earthworks are proposed to construct a levelled building pad (i.e. generally <
0.5 m cut and fill). If deeper fill embankments are required they should be limited to a maximum of 1 m in total
height and should be retained by engineer designed retaining walls.
Tree roots and organic rich topsoil must be stripped and stockpiled away from the construction area. Such
topsoil must not be re-used in structural fill, however may be retained on site for later use across landscaping
areas, if required. Sandy soils won from excavations on site may be reused as structural fill (where free of
vegetation i.e. excluding topsoil), subject to appropriate moisture adjustment.

Any fill should be compacted at moisture contents within the range of ±2% of optimum moisture content for
Standard Compaction. Fill particles greater than 100 mm must be excluded. Fill should be placed in
maximum 250 mm thick (loose thickness) layers and be compacted by repeated rolling to achieve a dry
density ratio of at least 95% of the maximum Dry Density Ratio (DDR) for building fill or 75% of the Dry
Density Index for cohesionless fills (e.g. sands).
Fill embankment edges must be over-filled by 0.5 m (horizontally) and then trimmed back to well compacted
material.
Confirmatory compaction testing should be carried out at regular intervals. Details for inspection and testing
of fill are given in Australian Standard AS 3798-2007 Guidelines on Earthworks for Commercial and
Residential Developments.




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