Response to Info Request - Attachment 5 - Geotechnical Report MCU18-0015 & RAL18-0001 · MCU18/0015

J000635-002-R-Rev1                                                                                November 2018


Further recommendations regarding site preparation for fill earthworks are provided in Section 61.3.
A working platform assessment must be carried out by a suitably qualified person (RPEQ) for heavy
machinery or equipment (e.g. crane or piling rig).

    6.1.2   Excavations
Investigation results indicate that the proposed excavations should be achievable using conventional
earthmoving equipment. Ripping may be encountered where colluvium is encountered (e.g. proposed Lot 3).
Horizontal direction drilling (HDD) for underground services must consider the presence of colluvium
containing boulders.

    6.1.3   Filling
Fill must not be placed on slopes exceeding 15o or on slopes within about 20 m of the creek, unless fully
supported by engineer-designed retaining structures (refer Section 6.2).
For the access driveway, the retaining structures must be constructed prior to placing fill. Compaction of fill
must be done without the use of vibration, to reduce possible impacts on slope stability. Careful attention
must be paid to moisture conditioning of fill during placement. It should be noted that settlement of the very
loose sand subgrade will likely occur immediately following fill placement.
Fill should be compacted at moisture contents within the range of -/+ 2% 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 3798-2007 Guidelines on earthworks
for commercial and residential developments. Fill should have a maximum particle size of 100 mm for an
uncompacted layer thickness of 200 mm and shall be compacted by repeated rolling to achieve a dry density
ratio of at least 98% of the Maximum Standard Dry Density for cohesive soils, or 75% Dry Density Index for
cohesionless soils.
In accordance with good construction practice, fill embankments should be ‘benched’ into slopes following
stripping and ‘over built’ then trimmed back to the well compacted material.
It is recommended that filling be carried out to Level 1 standards in accordance with AS3798-2007.

    6.1.4   Batter slopes
Unsurcharged cut batters in medium dense (or denser) sand and stiff clay up to 3 m vertical height should
not be formed steeper than 1V:2H. Flatter batters may be required if groundwater is encountered during
construction. Batter slopes in very loose/loose sands may be formed at 1V:3H.
Cut batters must be assessed by a geotechnical engineer from Core during excavation. Such assessments
should be undertaken progressively, with excavated face heights prior to assessment being limited to 1.5 m.
Cut batters will require re-vegetation to prevent erosion. This may require the use of hydromulching or
geotextiles to promote vegetation growth.
Positive support by engineer designed retained structures (refer Section 6.2) will be required where space
restrictions prevent trimming of batters to safe slopes, where slopes are surcharged or near movement
sensitive structures.

    6.1.5   Excavation support
Steeper slopes than those recommended in Section 6.1.4 will require excavation support. Options for
support include the following:

    Contiguous continuous flight auger (CFA) piles with infill grouting of voids

    Micropile A-frame structure
The use of sheet piles or driven ‘H’ sections may lead to stability impacts due to vibration during installation.
Detailed design for excavation support should be undertaken when the bulk earthworks have been confirmed
and the preferred method of excavation support selected. The detailed design must consider slope stability


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