Geotech

                              PROPOSED UNIT DEVELOPMENT
                              27 BOTTLEBRUSH AVENUE, NOOSA HEADS

Executive Summary
This report details the results of a geotechnical investigation undertaken for the proposed unit development
at 27 Bottlebrush Avenue, Noosa Heads. The investigation was performed by Tectonic for Novato Group
Pty Ltd ATF Bottlebrush Unit Trust.

The investigation comprised drilling of boreholes at three locations across accessible areas of the
development footprint. This report summarises the results of the investigation and provides geotechnical
recommendations regarding earthworks and footings, together with temporary and permanent basement
retention.
Preliminary architectural drawings indicate that the development will comprise a three-storey building, over
a single level basement carpark. Construction will likely include a combination of masonry and lightweight
materials (e.g. weatherboard cladding to walls etc.), and suspended concrete floors. No earthworks details
were provided at the time of reporting; however, provided plans indicate that excavations for the basement
would likely be in the order of about 6 m deep to the rear, daylighting at the front. Localised filling less than
0.5 m high is anticipated to form finished levels. Excavations will extend close to the site boundaries and




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therefore, some form of temporary retention will be required. Isolated deeper excavations may be required
for the lift overrun pit and other elements.
The subsurface conditions encountered in the boreholes are summarised as follows:

        Fill – comprising very loose to loose sandy gravel and silty sand to depths between 0.6 m and

     
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         1.3 m below ground level (BGL, boreholes BH1 and BH2 only); then or from the ground surface
         Natural Sands – comprising silty materials to about 1 m to 1.2 m BGL, then poorly graded sands
         initially, being loose to medium dense to depths between 2.2 m and 5.2 m BGL, then becoming
         medium dense to the borehole termination depths.

DCP testing was continued beneath the borehole termination depths, which indicates that the sands
become dense (or denser) at depths between 4.2 m and 6.3 m BGL.

No signs of groundwater seepage (‘springs’) were observed during our walk-over. Groundwater was not
encountered in the boreholes at the time of investigation.

Provided the recommendations within this report are adhered to, and subject to detailed design and
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construction of the footing and retention system by a suitably qualified and experienced structural engineer,
there would be a Low Risk to property from slope instability.

Excavations through the existing soils should be achievable using conventional earthmoving plant (e.g. small
or larger excavators with toothed buckets). Temporary unsurcharged cuts in the very loose to loose sands
could be formed at 1V:2H and at 1V:1H in medium dense (or denser) sand, for batters up to 3 m in height,
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provided groundwater seepage is not encountered and sands do not slough from the batter face as they dry
out. Space restrictions will limit battering of temporary cuts on the site and so some form of temporary
retention system will be required such as sheet, contiguous or secant pile walls.

Footings for the proposed development and any ancillary structures (e.g. retaining walls) must penetrate
through any fill materials and unsuitable natural soils (i.e. very loose to loose sands) to found at least 0.5 m
into medium dense (or denser) natural sands. Such materials were encountered below depths between 2.2 m
and 5.2 m BGL (existing ground levels). Thus, piled footings will be required unless excavations expose such
materials at or near foundation subgrade level. High-level footings would be suitable in excavation areas
where medium dense (or denser) natural sands are exposed at the subgrade level.

Given the sandy soil profile, where deepened footings are required (i.e. away from deeper excavations),
steel screw piles are considered to be an appropriate footing type. Due to the presence of loose sands,
together with the close proximity of adjacent residences, open bored piers or driven piles are not considered
to be suitable for this site.




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