RFI - slope stability reporting

RECOR Pty Ltd                                                                                   22393-001-Rev0
                                                                                                26 October 2022

4.2.1       Site Preparation and Trafficability
In construction areas, any relict construction elements, vegetation, tree stumps and large roots should be
stripped and ‘grubbed out’. Any organic rich topsoil should also be stripped and removed from site, based
on the boreholes, depths should generally range up to about 0.2 m depth. Organic topsoils and garden soils
must not be re-used as structural fill; however, small volumes may be retained on site for later use across
landscaping areas, if required.
The sand subgrade following stripping will likely be in a loose condition. Where slab on ground construction
is proposed (e.g. driveway) the ground surface should be compacted by several passes of a vibrating plate
compactor or small smooth drum roller (or similar), in conjunction with surface application of ample water.

Care must be taken with the use of vibratory equipment to ensure that there are no adverse impacts on
surrounding structures and underground services (e.g. existing Noosa Council and Unitywater infrastructure
along the site boundaries). The impacts from ground vibration must be closely monitored and managed
during construction. It would be prudent to conduct a dilapidation survey of neighbouring structures prior to
commencement of construction.

4.2.2        Filling
The existing sandy soils (excluding topsoil) may be reused as structural fill, subject to appropriate moisture
adjustment. It should be noted that compaction of such relatively ‘clean’ sands as structural fill requires the
addition of substantial volumes of water (‘flooding’) combined with the use of vibratory compaction
equipment (typically a minimum 4 tonne vibrating smooth drum roller or vibrating plate) to achieve required
compaction.

Should importation of fill be required, it is recommended that such fill should comply with the following:

       Minimum CBR of 10%
       Maximum plasticity index of 15%
       Shrink-swell index ≤ 1%
       Maximum particle size of 100 mm

Any fill should be compacted at moisture contents within the range of ±2% of optimum moisture content for
Standard Compaction. Select 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 with a small compactor to achieve a dry
density ratio of at least 95% of the Standard Maximum Dry Density for cohesive soils, or 70% Dry Density
Index for any imported cohesionless soils.

Confirmatory compaction testing should be carried out at regular intervals. A minimum of two tests per
vertical lift 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 embankment edges must be over-filled by 0.5 m (horizontally) and then trimmed back to well compacted
material.

4.2.3       Excavations
Excavations through the fill and natural soils encountered in the boreholes should be achievable using
conventional earthmoving plant (e.g. small excavators). Non-surcharged temporary cuts in the loose sands
could be formed at 1V:2H, and at 1V:1.5H in medium dense (or denser) sand, for batters up 2 m in height.
Although unlikely, if groundwater seepage is encountered or if sloughing of dry sand occurs at the batter
surface, flatter batters or temporary retention may be required. Deeper cuts, if required, should be specifically
assessed by Tectonic.
Permanent batters up to 1 m high (vertical height) may be battered no steeper than 1V:2.5H, or otherwise
supported by engineer designed retaining walls. Any permanent soil and fill batters will require erosion
protection (e.g. revegetation or surface protection).

If the above temporary batter slopes cannot be achieved, due to spatial restraints, temporary shoring would
be required (e.g. sheet piles, contiguous pile wall etc.). Excavations in close proximity to existing structures




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