RFI - 21327-001-Rev0 Plover St

                              PROPOSED RESIDENCE
                              34 PLOVER STREET, PEREGIAN BEACH

Executive Summary
This report details the results of a geotechnical investigation undertaken for a proposed multi-storey
residence at 34 Plover Street, Peregian Beach. The investigation was performed by Tectonic for
Nick and Katie Jorss.

The investigation comprised drilling of boreholes at two 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 retention.
Preliminary architectural drawings indicate that the development will comprise the construction of a two to
three storey split level building, with most of the lower levels excavated into the hillside. Construction will
likely include a combination of masonry and lightweight materials (e.g. weatherboard cladding to walls etc.)
and suspended concrete floors. A pool will be suspended above the central part of the lower level.
No earthworks details were provided at the time of reporting; however, provided plans indicate that
excavations for the lower level would likely be in the order of about 3 m deep in the western part of the site,
with the cut daylighting towards the east. Localised filling less than 1 m high is anticipated. Excavations will
extend close to the site boundaries and, therefore, some form of temporary retention will likely be required.
Isolated deeper excavations may be required for underground services and footings or other elements.
The subsurface conditions encountered in the boreholes are summarised as follows:

        Topsoil – comprising loose silty sand to 0.1 m below ground level (BGL); then
        Natural Sands – comprising loose, poorly graded sands to 2 m BGL, then becoming medium
         dense, increasing to dense (or denser) below depths of about 4.5 m to 5.2 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 RPEQ 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:1.5H 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, 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 at about 2 m BGL (existing
ground levels) in the boreholes. 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 a suitable foundation type. Due to the presence of loose sands,
together with the close proximity of adjacent residences, open bored or driven piles are not considered to be
suitable for this site.




10 September 2021
Report No. 21327-001-Rev0                               ii