geotech

                              PROPOSED UNIT DEVELOPMENT
                              9 BOTTLEBRUSH AVENUE, NOOSA HEADS

Executive Summary
This report details the results of a geotechnical investigation undertaken for the proposed residential unit
development at 9 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 include a combination of masonry and lightweight
materials (e.g. weatherboard cladding to walls etc.), ‘trimdeck’ roofing 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 up to about 4 m deep in the rear daylighting at the front, with
filling less than 1 m high anticipated. Excavations will extend close to the site boundaries and 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:

        Asphalt – 15 mm thick (borehole BH1 only); then
        Fill – comprising loose sandy gravel and silty sand to 0.8 m below ground level
         (BGL, borehole BH1 only); then or from the ground surface
        Natural Sands – comprising silty and poorly graded sands that were very loose/loose to depths of
         between 1.6 m and 2.2 m BGL; becoming medium dense (or denser) increasing to dense below
         about 4 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
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,
provided groundwater seepage is not encountered and sands do not slough from the batter face as they dry
out. It is expected that 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 piles.

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 1.6 m
and 2.2 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 at grade level away from excavation
areas, steel screw piles are considered to be a suitable foundation 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.




13 July 2021
Report No. 21169-001-Rev0                               ii