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

J000605-001-R-Rev1                                                                                         March 2018


Documentation regarding earthworks control and testing of the existing fill was not available at the time of
writing. As such, the fill is deemed ‘uncontrolled’.
5.2.2 Natural soils
A former topsoil layer of about 0.2 m to 0.3 m thick underlies the fill. The former topsoil layer comprises loose
to medium dense clayey sand, with abundant organic material present.
The former topsoil is underlain by alluvial/estuarine sand to about 5 m depth. The sand is typically medium
dense to very dense, but loose in borehole BH3 at 2 m to 4 m depth. The sand has varying fines content,
and contains traces of organic material and shell fragments in parts.
Below the sand, high plasticity firm to stiff alluvial clay was encountered up to between about 5.8 m and 6.5
m depth. The clay has varying sand content.
The firm to stiff alluvial clay is underlain by stiff to hard alluvial and residual clay, of medium to high plasticity,
to the investigation depth (6.5 m to 9 m BGL).
5.2.3 Groundwater
During auger drilling, groundwater levels were encountered between 0.9 m and 1.3 m depth.
Groundwater levels are expected to fluctuate in response to variations in rainfall, and are likely to rise close
to the ground surface during periods of heavy or prolonged rainfall.

6.0     GEOTECHNICAL COMMENTS & RECOMMENDATIONS
6.1 Site preparation & trafficability
All surface vegetation and organic-rich topsoil must be removed from building areas prior to construction.
Due to the potential for poor trafficability in soil across the site or in the base of the basement excavation,
particularly during periods of wet weather, it would be prudent to allow for the placement of a nominal 150
mm thick (or thicker depending on traffic loadings) granular layer to facilitate movement of construction
traffic.

A bearing pressure assessment must be carried out by a suitably qualified person for proposed working
platforms for heavy machinery or equipment.

6.2 Excavation characteristics & stability
Excavation for the basement (up to about 2.5 m BGL) is likely to encounter mainly loose to dense sands.
Such excavation should be achievable using conventional earthmoving equipment (e.g. tracked excavator).
Groundwater was encountered between 0.9 m to 1.3 m BGL during borehole drilling. Groundwater inflow is
therefore anticipated during basement excavation.
Dewatering will be required for the basement excavation (refer Section 6.2.1)
Medium dense to dense sand above the groundwater level would be expected to temporarily stand
unsupported at slopes of 1V:1H (without loads behind the batter crest). A minimum distance of at least
2.5 m (horizontal) between the crest of such batter slopes and any adjacent services or structural elements
is recommended.
Excavations in the wet sands are not expected to stand unsupported during the construction period, and will
require the installation of temporary support (refer Section 6.2.1)
Excavations close to the boundary (if required) must consider the presence of adjacent structures and
services. A dilapidation survey of adjacent structures is recommended prior to basement excavation, and
consideration must be given to construction vibration impacts.
Care should be taken to confirm underground service locations as instability of previous trench backfill can
impact the temporary support of the basement excavation if it encroaches on such conditions.




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