MCU25 0087 - Reference Document - Geotech assessment report (As Published) · MCU25/0087

        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
Document Set ID: 24631529
Version: 1, Version Date: 24/03/2026