Geotehnical Investigation Report · OPW22/0140

                              PROPOSED UNIT DEVELOPMENT
                              37 BOTTLEBRUSH AVENUE, NOOSA HEADS

Executive Summary
This report details the results of a geotechnical investigation undertaken for a proposed unit development at
37 Bottlebrush Avenue, Noosa Heads. The investigation was performed by Tectonic at the request of
Bottlebrush Property. 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 slope stability, earthworks and footings, together with advice for
temporary and permanent basement retention.

Architectural designs show a three-storey unit complex, over a single level basement carpark and living
space. Excavation will most likely be up to 4 m in depth, with filling likely to be less than 1 m high. Temporary
retention will be required as the basement excavation will extend close to some of the site boundaries.
The subsurface conditions encountered in the boreholes are summarised as follows:

        Pavement (pavers/synthetic matting) – 20 mm to 60 mm thick; then
        Fill – comprising mostly very loose, silty and gravelly sand to between 0.4 m and 1.2 m below
         ground level (BGL); overlying
        Aeolian Sands – comprising poorly graded sands that were loose to depths of between 1.1 m to
         2.5 m BGL in boreholes BH2 and BH3; then becoming medium dense (from 0.2 m BGL in BH1)
         and increasing to dense below depths of about 3.1 to 4.1 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 systems by a suitably qualified and experienced structural RPEQ,
there would be a Low Risk to property from slope instability.

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, unsurcharged cuts
could be formed at 1V:2H in the very loose to loose sands, and at 1V:1H in medium dense (or denser) sands,
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, such as sheet piles, may be required.

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 in the boreholes below
depths of about 1 m to 2.5 m BGL (existing ground levels), being shallower in the area of borehole BH1 where
it is assumed the site was previously cut down to form the driveway. High-level footings would be suitable in
excavation areas where medium dense (or denser) natural sands are exposed at the subgrade level. Piled
footings would be required unless excavations expose such materials at or near foundation subgrade level.

Given the sandy soil profile, where deepened footings are required, 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
buildings, open bored piers or driven piles are not considered to be suitable for this site.




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