geotech report · 132003.220660.5

6.8     Floor Slabs
Whilst slab-on-grade construction is theoretically feasible for the floor slabs, it will be difficult to complete
high quality earthworks on a small site such as this, as it would require removing and re-compacting the
existing poorly compacted fill and very loose sands. Also, on-grade floor slabs in contact with a mix of
foundation soils would result in differential movements, and potential cracking of the floor slabs. The
differential settlements would also be exacerbated at the interface with suspended sections of floor slabs.

Therefore, the proposed floor slabs should be designed as suspended over the very loose sands and/or poorly
compacted fill between piles founded in loose (or denser) sands. As noted in Section 6.7 above, this would
also allow the loadings to be transferred below the existing sewer pipe invert.

For floor slabs suspended over soil subgrade areas, the subgrade preparation would comprise the removal
of any topsoil and/or any soil containing organics, completion of and re-profiling of site surface levels and
the nominal tracking of ‘formwork fill’ to the required subgrade level.



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



6.9.1 Subgrade Preparation
Prior to placement of engineered fill to form the proposed grass surfaced area to the east of the existing
house, the soil subgrade should be prepared as follows:
•     Following removal of 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.
•     To assist with proof rolling, we recommend that a thin layer of road base (75mm thick) be placed over
      the sand subgrade to provide confinement and prevent shearing during rolling.
•     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).
•     Over sloping areas, benches should be cut into the slope to accommodate the roller and facilitate more
      effective proof rolling and keying in new engineered fill layers.
•     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.




32032URrpt                                          17