Attachment 2- soil stability report · MCU14/0017

                                                                                    Report No. 13N 682




It is further recommended that cut slopes be inspected at intervals during construction by a suitably
experienced geotechnical professional.

It is expected that spoil excavated on site will be re-used to construct the fill platforms proposed
under the garage and pool.

Based on the borehole logs, no material of maximum particle size greater than 100mm is
expected. If material greater than 100mm diameter is encountered this should be removed prior to
the placement of fill. All fill should be placed in uncompacted layers no greater than 200mm
thickness. Layers should be compacted with either a small roller or compactor to a minimum
density index of 70% (AS1289 5.6.1) for the relatively cohesionless soils expected at the site.

Compaction testing of the backfilled material should be undertaken at regular intervals in
accordance with Australian Standard AS3798-2007 “Guidelines on Earthworks for Commercial and
Residential Developments”.

All filling should be benched into the natural soil with layers over-filled horizontally by 1m and
trimmed back to the required profile ensuring finished surfaces are well-compacted.

Any fill placed greater than 1m height should be retained by an engineer designed and approved
retaining structure founded in dense silty sand at depths greater than 3.6m below surface.

       3.2     Drainage

While the sandy nature of the soils encountered during the borehole investigation should be
relatively free draining it will still be necessary to ensure adequate drainage to direct surface water
away from footings of proposed structures. This could be achieved by the construction of shallow
spoon drains at the crest of cut slopes and batters which are directed away from construction
areas and towards natural drainage (gullies).

Some sediment and erosion management in the form of sand bags, sediment socks or temporary
retention/settlement pits may be required to minimise surface erosion and the amount of
suspended sediment being directed into the natural drainage.

Where retaining structures are to be constructed, it is recommended that subsurface drainage be
installed behind these structures to mitigate the development of hydrostatic pressure in the
retained soils. Adequate subsurface drainage could comprise the installation of slotted PVC
agricultural pipe wrapped in a suitable filter „sock‟ of geotextile or similar and placed in a free
draining gravel backfill.

Should surface seepage be encountered during or following construction it is recommended that
this flow is also directed away from all structures towards stormwater pits or street-side drainage.




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