Appendix B - Geotechnical Investigation Report

fill but would most likely require moisture conditioning which could result in delays. Also there may be a
shortfall in site won materials and imported fill would be required.

We recommend that engineered fill comprising well graded imported granular materials such as demolition
rubble would be suitable for treatment of poor subgrade areas and for backfilling retaining walls. The
imported engineered fill must be free of contaminants or deleterious substances and has a maximum particle
size not exceeding 40mm. Imported well graded granular fill should be compacted to at least 98% of SMDD
and within 2% of their SOMC. The compaction requirement may be reduced to 95% of SMDD in landscaped
areas, where settlement can be tolerated. Such fill should be compacted in horizontal layers as described
above. Care will be required to ensure excessive compaction stresses are not transferred to the retaining
walls.

Density tests should be carried out at the frequencies outlined in AS3798 (Table 8.1) for the volume of fill
involved. At least Level 2 testing of earthworks should be carried out in accordance with AS3798. Any areas
of insufficient compaction will require reworking.

As an alternative, single sized granular material (or ‘no fines’ gravel) may be used as backfill to the landscape
retaining walls and this would also act as the drainage behind the wall and would only require nominal
compaction (with no compaction testing). The drainage material should be wrapped in a non-woven
geotextile fabric (e.g. Bidim A34) to act as a filter against subsoil erosion. Further, retaining wall backfill
should be provided with a cap of at least 0.3m thickness of compacted crushed sandstone or clay at surface
level to reduce the likelihood of surface water surcharging the retaining wall.



6.9    Wastewater Treatment and Disposal
We note that the ASI “Site Soil Evaluation” report as recommended the following method of on-site effluent
disposal comprise an Advanced Secondary Treatment with an Advanced Enviro Septic System (AES)
Transpiration Bed.

For further details refer to the ASI “Site and Soil Evaluation” report.



6.10 Overall Effect of Development on Stability
We do not consider that the development will have any detrimental impact on the stability of the site. This
is on condition that the design and construction of the proposed development is completed in accordance
with the geotechnical advice presented in this report.



7     CONCLUSION
We consider that the site is suitable for the proposed development.




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