Appendix H Geotechnical Investigation - 14-16 Mary Street, Noosaville - Bounce Hostels 15.6.2018

J000605-001-R-Rev1                                                                                     March 2018



Executive Summary
This report presents the results of a geotechnical and acid sulfate soil (ASS) investigation carried out by
Core Consultants Pty Ltd (Core) for a proposed development at 14 to 16 Mary Street, Noosaville.
The proposed development comprises four two-level pavilion-style buildings, with a central swimming pool
and single-level basement carpark (up to about 2.5 m depth below existing ground level) under one of the
buildings. Minor fill earthworks (up to about 0.5 m) are proposed.
Four boreholes were drilled, under engineering supervision, across the proposed development footprint
using a utility-mounted auger drill rig. Borehole depths ranged between 6.5 m and 9 m below ground level.
Dynamic cone penetrometer testing (DCP) was conducted within the boreholes.
The subsurface conditions encountered in the boreholes generally comprised:

       About 1 m of dense sandy fill, underlain by
       A former topsoil layer of about 0.2 m thick, over
       Sand alluvium to about 5 m depth (typically medium dense to very dense, some loose)
       Firm to stiff clays to between 5.8 m and 6.5 m depth, underlain by
       Stiff to hard clays to the investigation depth.
Groundwater was encountered in all four boreholes at between 0.9 m and 1.3 m depth.
Dewatering will be required for the basement excavation. Excavations in the wet sands are not expected to
stand unsupported during the construction period and will require the installation of temporary support. Sheet
piles founded in the underlying clay are considered a suitable option for temporary support. Provided that the
sheet piles are founded in the clay, sump pumps in the excavation base should be a suitable dewatering
method. Alternatively, spear-point dewatering around the basement perimeter will be required. Consideration
must be given to the effects of dewatering during construction and the effect of groundwater drawdown on
neighbouring properties and in-ground services. Drawdown will likely be less for sheet piles founded in the
underlying clay combined with sump pumps in the excavation base, rather than spear-point dewatering. To
reduce groundwater drawdown, consideration could be given to the re-injection of groundwater outside the
temporary shoring system (provided that the shoring system is suitably designed for hydrostatic pressure).
Due to the presence of uncontrolled fill up to 1.1 m thick, as well as loose natural sand to about 4 m depth,
the use of high-level footings is not recommended. The proposed at-grade buildings (i.e. without basement)
could be supported on screw piers founded in the dense sand or stiff clay. Reinforced concrete driven piles,
timber push piles or continuous flight auger (CFA) piles could also be considered. Bored piles will likely
encounter construction difficulties due to the loose sand and high groundwater. The proposed basement
could be supported on a raft, pad footings or screw/driven piles in the dense sand or stiff clay. If a raft or pad
footings are adopted, founding conditions must be confirmed following basement excavation through
additional DCP testing by a geotechnical engineer from Core. If loose sands are encountered, over-
excavation and compacted replacement may be required (possibly up to 1 m depth or more) to support a raft
or pad footings in the sand. A design allowable bearing pressure of 400 kPa may be adopted for a raft or pad
footings in the dense natural sand.
The results from this investigation indicate that potential ASS (PASS) was encountered in the natural sands.
A lime treatment rate of 20 kg CaCO3/m³ is recommended and in accordance with the SPP14 guidelines for
Category XH treatment, a stand-alone ASS Management Plan (ASSMP) must be provided.




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