Appendix B - Geotechnical Investigation Report

in some degree of differential deflection, and potential cracking of the floor slabs. If this cannot be accepted,
then the floor slabs should be suspended (and provided with void formers) as described in Section 6.7 above.

The following earthworks recommendations should be complemented by reference to AS3798-2007
“Guidelines on Earthworks for Commercial and Residential Developments”.



6.8.1 Subgrade Preparation
Prior to placement of engineered fill for treatment of poor subgrade areas and/or construction of on-grade
floor slabs, the soil subgrade should be prepared as follows:
   Following removal of any existing paved surfaces, and stripping of topsoil and/or any root affected soils,
    any remaining poorly compacted fill should be removed, as directed by the geotechnical engineer.
   Proof roll the soil subgrade with a minimum 2 tonne deadweight smooth drum roller, using the static
    (non-vibration) mode, following thorough moistening of the sand subgrade. Where access is restricted,
    proof rolling is expected to require the use of a hand-held plate/sled compactor.
   If soil softening occurs after rainfall, then the clay subgrade should be over-excavated to below the depth
    of moisture softening and replaced with engineered fill. Conversely, if a clayey subgrade exhibits
    shrinkage cracking, then the surface should be lightly watered and rolled until the shrinkage cracks are
    no longer evident.
   Proof rolling should be closely monitored by the geotechnical engineer to detect soft or unstable areas
    which should be removed and replaced with engineered fill (as outlined below). Care should be taken
    not to over-compact the clayey subgrade.
   Care should also be taken when using vibrating equipment not to cause damage to any adjacent
    structures. The vibrations should be qualitatively monitored by site personnel and if there is any cause
    for concern then proof rolling should cease and further advice sought.



6.8.2 Drainage During Construction
The subgrade will comprise clay soils which may be found to be unstable if proper site drainage is not
implemented during construction. It is therefore important to provide good drainage in order to promote
run-off and reduce ponding. Earthworks platforms should be graded to maintain cross-falls during
construction. If the clays are exposed to periods of rainfall, softening may result and site trafficability will be
poor. If softening occurs, the subgrade should be over-excavated to below the depth of moisture softening.
The material removed should be replaced with engineered fill. Trafficability may be improved by the use of
a sacrificial surface layer of crushed demolition rubble.



6.8.3 Engineered Fill
For treatment of any poor subgrade areas and backfill to retaining walls, engineered fill should be used.

Engineered fill should be free from organic materials, other contaminants and deleterious substances and
have a maximum particle size not exceeding 40mm. The locally excavated clays may be used as engineered

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