Geotechnical Report

 J000206-001-R-Rev0                                                                                      April 2016


6.0      GEOTECHNICAL COMMENTS AND RECOMMENDATIONS
           Earthworks
Earthworks should be carried out in accordance with Australian Standard AS 3798-2007 Guidelines on
Earthworks for Commercial and Residential Developments.
6.1.1         Site Preparation & Trafficability
Site preparation in building and pavement areas should include the following:

       Removal of trees, tree roots systems, and other vegetation;

       Strip the surface of vegetation, organic matter, organic rich soils (topsoils) and severely root affected
        soils. Fine rootlets and organics in the soils were encountered in test pits up to about 0.3 m depth,
        however it is anticipated that grubbing of tree stumps and tree roots will require localised stripping to
        greater depths. Root affected sols with tree roots up to about 50 mm to 100 mm diameter were noted
        in some of the test pits to depths of up to 0.6 m.

       ‘Proof roll’ the stripped surface by several passes of a minimum 10 tonne roller to identify loose or soft
        areas.
       Depressions formed during removal of large tree root systems should be backfilled with select fill and
        compacted in layers
An experienced geotechnical engineer from Core should carry out an inspection of the subgrade 'proof roll'.
Loose/soft areas or uncontrolled fill areas identified by proof rolling and inspection will require treatment by
either of the following methods:

       Over-excavation and replacement with suitable fill compacted in layers (refer Section 6.1.4); or
       Re-compaction of the loose or soft material provided that it does not contain substantial organic matter
        or deleterious substances Due to the potential for poor traffickability across the site, it would be
        prudent to allow for the placement of a nominal 150 mm thick (or thicker) granular layer to enable
        movement of construction machinery.
6.1.2         Excavations
Excavation for footings and service trenches are expected to encounter firm to hard clays and possibly
extremely low strength siltstone. Excavations in soils and extremely low strength rock should be achievable
using conventional small to medium sized earthmoving equipment. Ripper attachments may be required
where low strength rock is encountered.
Shoring would be required to maintain stability and enable safe personnel entry into trenches (with vertical
sides) deeper than 1 m.
6.1.3         Filling
Based on the subsurface conditions encountered in the test pits, site won material from excavations will
generally be suitable for reuse as structural fill provided materials are free from deleterious material, oversize
(>75 mm size) particles and organic matter. Any imported fill should similarly exclude such materials.
Where filling is proposed as part of earthworks, the following measures should be adopted:

   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.
   Fill should have a maximum particle size of 100 mm for an un-compacted 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.
        Higher grades of compaction will be required for pavement subgrades and base courses.
   Proposed fill should have a minimum CBR value of 10%, and maximum plasticity index of 15%.
   Sloping ground should be benched to key in fill material and optimize compaction.

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