Attachment 5 - Geotechnical Assessment · MCU18/0015

 

- “RTI-117055 Fotio-B393

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Noveimber 2003 -9- 03632248-001

 

7.0 GEOTECHNICAL ADVICE
7.1 Earthworks
7.1.1 Site Preparation

Prior to any earthworks activities, organic rich topsoil must be stripped and removed from the
building areas. This material must not be used as fill to support any structural loads, however it
may be used in landscaping areas. Where footings are proposed to penetrate through new fill, it
would be prudent to ‘pre-excavate’ shallow colluvium (which contains cobbles and boulders)
and replace it with ‘clean’ soil that is free of particles greater than 100 mm. This should enable
less difficult excavation for footings following placement of fill.

7.1.2 Excavation

The results of the investigation indicate that the proposed excavations should encounter the
following subsurface conditions:

© Western (dune) side of creek: mostly very loose grading to dense sands, with possibly
dense to very dense colluvium (diorite cobbles and boulders with about 30% silty sand)
below about 1 m depth adjacent to‘the ereek. The depth of overlying sand increases up
slope to in excess of 6 m.

e Eastern side of creek: mostlymedium to,dense silty sand and stiff sandy clay colluvium
overlying very stiff to\hard inferred residual sandy/silty clay. Numerous high strength
diorite ‘core stone’ boulders below about 1.5 m depth.

Considering the above, excavation to the depths shown in the design drawings should be
achievable using conventional_carthmoving equipment, possibly with the assistance of
‘ripper’ attachments for efficient excavation of the colluvium and to dislodge large boulders.

7.1.3 Filling

Fill must not be placed on slopes exceeding 15° or on slopes within about 20 m of the creek
(Section 6), unless fully supported by engineer designed retaining structures (ref. Section 7.2).

Fill should be compacted at moisture contents within the range of -2% to +1% of optimum
moisture content for Standard Compaction. Confirmatory testing must be carried out at
regular intervals. A minimum of two tests per 300 mm vertical interval is recommended
where structural fill heights are to exceed 300 mm. Further details for control and testing of
fill are given in Australian Standard AS 3798-1996 “Guidelines on Earthworks for
Commercial and Residential Developments". Select fill should have a maximum particle size
of 100 mm for an uncompacted layer thickness of 200 mm and shall be compacted by

Golder Associates