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

6.          Geotechnical Recommendations
Based on the modelled 100-year ARI erosion cut profile, and the subsequent regressive failures of the
slope to equilibrium (27°), the subject site would require protection from erosion.
From a geotechnical perspective, the requisite FOS could be achieved utilising a shear pile wall
positioned along the eastern property boundary. However, the property is situated on the western
(landward) 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 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.
The adopted structure should comprise piles structurally tied together at the surface using a steel-
reinforced concrete capping beam. An ‘A-frame’ structure may ultimately be required (i.e. vertical and
raked piles) to achieve the required shear force resistance, at least if micro-piles are adopted, especially
where allowance is given for the anticipated upstand ranging up to about 5 m high indicated by the
stability analyses.
A summary of the minimum piling requirements for the shear pile wall is given as follows:
Case 4: Shear pile wall along eastern edge of building area:
    Minimum Pile Length (below existing ground): 12 m
    Upstand Height:                                  5m
    Unfactored resistance to normal shear forces:    160 kN/m*
*The quoted resistance to normal shear forces is as utilised within the scope of the program Slope/W. It is
noted that this does not necessarily relate to actual design parameters, and designers must undertake finite
element analysis to assess soil/structure interactions and calculate both bending and shear stresses in the
piles. Retaining structures should also undergo rigorous checks of global and internal stability. The designer
must be satisfied that the geotechnical data presented is adequate to allow the analyses to be undertaken
with a high degree of confidence.
For a non-contiguous pile wall system such as micro-piles, a grout ‘curtain’ would need to be installed
along the length of the wall to prevent the flow of sand between the piles. Based on the highest
modelled vertical face of about 5 m height along the eastern boundary, such a grout ‘curtain’ should be
installed down to at least 7 m below the ground surface (existing).
Whilst the proposed structure would prevent erosion along the eastern boundary of the property, there
is potential for the design erosion event to remove sand from the neighbouring properties to the north
and south, exposing the side boundaries of the site to instability and erosion. The extent of the side
boundary erosion protection required has been determined by a line drawn at 27° extending upwards
from the estimated dune toe, following extreme storm erosion, and subsequent retrogressive
failures. Erosion protection is required to extend from the shear pile wall to an equivalent distance of
8 m from the eastern property boundary, along the northern and southern boundaries. The erosion


Geotechnical investigation
19 November 2025 | 25289-001-Rev0                                                                              16