RFI -Attachment 6 - Geotechnical Investigation Report CORE.pdf

Walsh Consulting Engineers




5.2       Ground Conditions
Subsurface conditions encountered in the boreholes generally comprise loose/medium dense to very dense
aeolian (dune) sand. Shallow sand fill (re-worked natural soil generally less than 1 m in depth) was
encountered in some boreholes. The fill is deemed ‘uncontrolled’ as defined in Australian Standard AS 3798-
2007 Guidelines on earthworks for commercial and residential developments (AS 3798-2007).
Groundwater was not encountered in the boreholes during drilling. Due to the relatively permeable nature of
the sands, and the sloping nature of the site, prolonged high groundwater levels or periods of waterlogged
soil are not anticipated.

6.0        GEOTECHNICAL COMMENTS & RECOMMENDATIONS
6.1       Earthworks
        6.1.1   Site Preparation
Site preparation in building and pavement areas should include the following:

▪       Strip the surface of vegetation, organic matter, organic rich soils (topsoils), severely root affected soils,
        and unsuitable material.

▪       ‘Proof roll’ the stripped surface by several passes of a minimum 10 tonne roller to identify loose or soft
        areas. Proof rolling in areas of cut may be deferred until after bulk excavation is completed.
An experienced geotechnical engineer should carry out a visual assessment of the subgrade 'proof roll'.
Loose/soft areas or uncontrolled fill identified by proof rolling will require treatment by either of the following
methods:

▪       Over-excavation and replacement with suitable fill compacted in layers, or;
▪       Re-compaction of the loose or soft material provided that it does not contain substantial organic matter
        or deleterious substances.

        6.1.2   Trafficability & Working Platforms
Due to the potential for poor trafficability across the site, particularly following wet weather of if loose sands
at the surface are disturbed and dried out, it would be prudent to allow for the placement of a compacted
granular fill layer (e.g. 150 mm) particularly in haul road and laydown areas.
A working platform assessment must be carried out by a suitably qualified person (RPEQ) if heavy
machinery or equipment (e.g. crane or piling rig) are proposed.

        6.1.3   Excavations
Excavations into the sands should be achievable using conventional earthmoving equipment (e.g. large
tracked excavators).

        6.1.4   Filling
The following recommendations should be considered for fill material placement and compaction:

    ▪     Site-won fill should be compacted at moisture contents within the range of +/-2% of OMC for Standard
          Compaction
    ▪     Confirmatory compaction testing must be carried out at regular intervals. Details regarding
          recommended test frequencies are provided in Table 8.1 of AS 3798-2007
    ▪     Fill should have a maximum particle size of 100 mm for an uncompacted layer thickness of 250 mm
          and should be compacted by repeated rolling
    ▪     Fill should be compacted 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


J001390-001-R-Rev0                                      6