Geotechnical Report

                             PROPOSED UNIT DEVELOPMENT
                             31 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.

6.1       Development Limitations
It is anticipated earthworks will include cuts for the basement level of up to about 3 m deep in in the rear 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
Any uncontrolled fill, existing mulch, and organic rich topsoil must be stripped from the development areas,
whilst vegetation, tree stumps and large roots must be ‘grubbed out’. Based on the boreholes, mulch and
topsoil stripping depths should generally range between 0.1 m and 0.2 m BGL, however deeper pockets of
mulch/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 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.

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 watercourses.

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 existing soils should be achievable using conventional earthmoving plant (e.g. small
or larger excavators with toothed buckets). Temporary cuts in the very loose to loose sands could be formed
at 1V:2H and at 1V:1H in medium dense 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.

If filling or permanent cuts exceed 1 m, then these 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).

If the above temporary batter slopes cannot be achieved, due to spatial restraints, temporary shoring will be
required (e.g. sheet piles). Excavations in close proximity to existing structures, including on neighbouring
properties, will need to be specifically designed to prevent undermining. It is recommended that footing


17 December 2020
Report No. 20370-001-Rev0                              10