25289-001-Rev0 - The Esplanade (1)-compressed

Executive Summary
This report details the results of a geotechnical investigation undertaken for a proposed residential
development at 17 The Esplanade, Sunshine Beach. Preliminary architectural drawings indicate that the
development will consist of the construction of a three-level structure, which includes a single level
basement.
The boreholes and in situ test results indicate a subsurface profile of relatively poorly graded dune sands
to the maximum investigation depth of 6.9 m below ground level (BGL). Very loose to loose sands were
deepest in borehole BH2, extending to 2.4 m BGL, overlying medium dense sand to depths of 5 m BGL,
with underlying dense (or denser) sands. The other borehole and DCP tests indicated shallower
transitions to both medium dense and dense sands.
Slope stability modelling was carried out considering short-term erosion from a 100 year average
recurrence interval extreme storm event (as nominated by the appointed coastal engineering experts,
Moffat & Nichol (M&N)); and anticipated regression of the dune over time. The M&N assessment
indicated that a large portion of the high dune face would be affected by such a future erosion event,
extending approximately 17 m laterally into the dune face; with a localised scarp crest at around RL 23 m
AHD. The erosion cut was shown to extend to within 13 m of the subject site’s eastern boundary.
Subsequent regressive failures of the erosion profile would then be expected to occur, until the dune
face reached a slope angle of about 27°, which could encroach by about 7 m into the subject site.
The property is situated on the western side of The Esplanade road reserve, which acts as a buffer
between the beach, dune slope and the site. As a result, maintaining the integrity of the road reserve
would, in turn, help protect the property. Since the road reserve is owned and managed by Noosa
Council (NC), it is anticipated that NC would prioritise its protection before any erosion progresses
beyond the reserve and reaches the site. However, if NC determines that the property requires its own
protective measures, a shear pile wall would need to be constructed along the eastern boundary.
Given our understanding of the ground conditions and the predicted future slope geomorphology, a
shear pile wall founded at depth into the dense (or denser) sands may be required to protect the site
from coastal erosion. Subject to detailed design, secant or contiguous shear piles, possibly with
additional structural support (e.g. raked piles, ground anchors), would be required to cater for the
anticipated ‘upstand’ of about 5 m following future erosion (as indicated by our analysis). The shear piles
would likely need to be at least 12 m deep BGL. Protection against erosion and adverse interaction with
adjacent properties would also be required. This could consist of a grout curtain extending from the
eastern boundary at least 8 m westward along the northern and southern boundaries.
The following additional recommendations are provided for the proposed development:
 The proposed residence and any ancillary structures must be supported by footings founded at least
   1 m into natural medium dense (or denser) sands. In the areas of deeper cut (i.e. the basement level),
   high level footings may be adopted. Elsewhere, piles will be required.
 Excavations close to site boundaries may necessitate the installation of temporary shoring.
 Ground vibrations during construction must be minimised and monitored. Where excessive vibrations
   occur, alterations to construction techniques may be required. It is recommended that a dilapidation
   survey of adjoining structures be completed prior to construction.
 Collected roof water should be directed by pipes to the council stormwater system along The
   Esplanade. Hydraulic design should be such that under no circumstances are uncontrolled
   stormwater flows permitted over the dune face.


Geotechnical investigation
19 November 2025 | 25289-001-Rev0                                                                         ii