Geotech

                             PROPOSED UNIT DEVELOPMENT
                             27 BOTTLEBRUSH AVENUE, NOOSA HEADS

6.3      Earthworks – General
6.3.1       Site Preparation and Trafficability
Following removal of the existing buildings and associated construction elements (e.g. footings, services,
etc.), any tree stumps and large roots should be ‘grubbed out’. Any organic rich topsoil and uncontrolled fill
should then be stripped and set aside. Based on the boreholes, topsoil stripping depths should generally
range between 0.1 m and 0.2 m BGL, with uncontrolled fill encountered to 1.3 m BGL (existing ground
levels) in borehole BH1. It is possible that deeper pockets of topsoil or uncontrolled fill may exist and
deeper, localised grubbing out of tree roots may be required.

Topsoil materials must not be used in structural fill; however, may be placed across landscaping areas.
Unsuitable natural material such as any saturated, loose or soft materials encountered should also be
removed during subgrade preparation for bulk earthworks.

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 vibrating plate). Care must be taken with the use of vibratory equipment (e.g. compactors or sheet piling)




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to ensure that there are no adverse impacts on surrounding structures. 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.
The exposed natural subgrade following excavations will likely be in a loose condition and must be
compacted by several passes of a vibrating plate or minimum 4 tonne vibrating smooth drum roller, in
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conjunction with surface application of ample water, to achieve the required compaction.

Due to the potential for development of poor trafficability during construction, placement of a minimum
150 mm thick granular working platform may be required across laydown areas. Specific platform design
would be required prior to mobilisation and trafficking of any heavy mobile plant on the site (e.g. mobile
cranes, concrete pumps or piling rigs).

Due to the highly permeable nature of the sands at this site, stormwater is expected to rapidly infiltrate the
ground, making un-sealed surface drainage ineffective for the control of flows. Any sealed areas should be
graded to ensure free drainage of stormwater away from construction areas, and to a control point(s).

6.3.2       Excavations
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Excavations through the soils should be achievable using conventional earthmoving plant (e.g. small or
larger excavators with toothed buckets). Temporary unsurchaged cuts in the very loose to loose sand could
be formed at 1V:2H, and at 1V:1.5H in medium dense (or denser) sand, for batters up to 3 m in height. Flatter
batters or temporary retention may be required if groundwater seepage is encountered or if sloughing of dry
sand occurs at the batter surface. Deeper cuts, if required, should be specifically assessed by Tectonic.
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Permanent cuts or fills greater than 1 m must be retained. Permanent cut and fill batters up to 1 m high shall
not exceed 1V:2.5H. Any permanent soil and fill batters will require erosion protection (e.g. revegetation or
surface protection).

Due to spatial restraints and the depth of excavations proposed, temporary shoring will be required (e.g.
sheet piles) as per the recommendations in Section 6.5 below. Excavations in close proximity to existing
structures and infrastructure (e.g. sewer main along the northern and eastern boundaries), including on
neighbouring properties, will need to be specifically designed to prevent undermining. It is recommended
that footing exposures or confirmation of existing foundations via certified building plans be undertaken to
assess the possibility of undermining. If undermining is a potential issue the existing structures may need to
be underpinned or excavations may require temporary shoring.

The advice of a suitably qualified and experienced RPEQ structural engineer must be sought regarding any
potential undermining and design and construction of any underpins/temporary shoring (if required).
The above recommendations do not supersede any existing safety regulations or legislation applicable to
excavations (e.g. limits on personnel entry into trenches).



10 November 2021
Report No. 21286-001-Rev0                              10