Geotehnical Investigation Report · OPW22/0140

                             PROPOSED UNIT DEVELOPMENT
                             37 BOTTLEBRUSH AVENUE, NOOSA HEADS

6.0      GEOTECHNICAL RECOMMENDATIONS
General recommendations to help maintain the stability of the site are given in the document Some
Guidelines for Hillside Construction, which is attached.

Tectonic must review design plans once they are available to confirm recommendations given herein
adequately address the proposed works.

6.1      Development Limitations
It is anticipated earthworks may include cuts for the basement level of up to about 4 m deep with only minor
filling expected to be required up to about 1 m in height to form finished surface levels. Should proposed
cuts/fills exceed this quantity, Tectonic must assess the impacts on slope stability before construction.

6.2      Earthworks – General
6.2.1       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 site observations, topsoil (where present) stripping depths
should generally range between 0.1 m and 0.2 m BGL, with uncontrolled fill encountered to depths of 0.4 m
to 1.3 m BGL. It is noted 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)
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
conjunction with surface application of ample water, to achieve the required compaction.

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

Construction areas and surrounds should be graded to shed surface water runoff. Swale drains should be
constructed along the crest and toe of any cuts, and above fill batters, where possible. Drains are to be
graded to discharge collected waters to a control point(s) before release into existing stormwater
infrastructure.
It should be noted that during wet weather, the natural soils may cause sediment run-off. Appropriate
erosion and sediment control measures must be installed prior to commencement of earthworks at this site.

6.2.2       Excavations
Excavations through the soils encountered in the boreholes 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:1H 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 unretained cuts, if required,
should be specifically assessed by Tectonic.


13 May 2022
Report No. 22151-001-Rev0                              10