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

protection shall taper from a minimum depth of 2 m BGL in the west, deepening to the east to tie into
the shear pile wall along the eastern edge.
Whether the pile wall will also need to extend around the side boundaries will depend on the dimensions
and strength of the grout curtain installed and its ability to provide at least emergency support to the
retained sand. This should be considered as part of the detailed design.
General geotechnical recommendations for site development are provided in the following sections.


6.1         Earthworks
Bulk excavations in the order of up to 4 m depth are anticipated for the basement level construction.
Isolated deeper excavations may be required for underground services and footings. The pool is shown
to be below ground, and will require excavation of up to about 3 m below existing ground levels, close to
the site’s northern boundary. Filling is anticipated to be for landscaping only, and should be less than
0.5 m high.
The advice give herein should be treated as preliminary to aid in project planning, and Tectonic must
review detailed design drawings for the residence prior to construction.

6.1.1       Site Preparation and Trafficability
Following clearing of existing vegetation, any tree stumps and large roots should be ‘grubbed out’. Any
organic rich topsoil should then be stripped and set aside. Similarly, all foundations and remaining
structural elements from the existing residence should be removed. Based on the boreholes and site
observations, stripping depths to remove existing unsuitable upper soils should be relatively shallow,
however, deeper areas of unsuitable materials may be present across the site, particularly related to the
existing structure (e.g. retaining wall backfill, service trenches, footing excavations). Topsoil materials
must not be used in structural fill; however, may be placed across landscaping areas.
It should be noted that compaction of such relatively ‘clean’ sands as structural fill requires the addition
of substantial volumes of water (‘flooding’) combined with the use of vibratory compaction equipment
(typically a vibrating plate). Care must be taken with the use of vibratory equipment (e.g. compactors or
sheet piling) to ensure that there are no adverse impacts on surrounding structures. The impacts from
ground vibration must be closely monitored and managed during construction. It would be prudent to
conduct a dilapidation survey of neighbouring structures prior to commencement of construction; and
furthermore it is recommended that a suitably qualified and experienced civil/structural RPEQ is engaged
to provide a vibration management plan for the proposed construction works.
The exposed natural subgrade following excavations will likely be in a loose condition (even where
indicated to be denser in our investigation boreholes) and must be compacted by several passes of a
vibrating plate or minimum 4 tonne vibrating smooth drum roller, in conjunction with surface application
of ample water, to achieve the required compaction.
Due to the potential for development of poor trafficability during construction, placement of a minimum
150 mm thick granular working platform may be required across laydown areas. Specific platform
design would be required prior to mobilisation and trafficking of any heavy mobile plant on the site (e.g.
mobile cranes, concrete pumps or piling rigs).
Due to the highly permeable nature of the sands at this site, stormwater is expected to rapidly infiltrate
the ground, making un-sealed surface drainage ineffective for the control of flows. Any sealed areas




Geotechnical investigation
19 November 2025 | 25289-001-Rev0                                                                            17