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

        achieved by helical steel anchors (similar to screw piles); and the proximity to neighbouring structures
        would require permissions to be obtained for subterranean access. Therefore, where lateral support by
        cantilever only is not feasible, it is suggested that internal struts/propping be considered to provide
        lateral restraint for the shoring system.
        Anchored or propped sheet piles may require pre-drilling to prevent adverse vibrations during sheet pile
        installation (where penetration of the deeper dense sands is required).
        Other shoring methods that could be considered include bored contiguous or secant piles.
        Conventional non-contiguous or soldier pile walls are not feasible for the proposed development due to
        the likelihood that loose sands would ‘flow’ through gaps between the piles. Their use may however be
        possible where additional grout panels are included in the design.
        An advantage of contiguous or secant pile wall retention systems is that they are ultimately used for the
        permanent walls, whereas sheet piles would be temporary to provide retention during construction only,
        therefore requiring a permanent structural wall to be constructed. Bored pile walls generally require
        greater width (horizontally) for installation as compared to sheet piles and are often more expensive.
        The advice of a specialist shoring contractor must be sought regarding feasibility, design and installation
        of the proposed retention system. It will be necessary to conduct numerical analysis to optimise the
        retention system. Detailed design will also need to account for relevant factors of safety to maintain the
        temporary and long-term stability of the retention system.
        Retaining structures greater than 1 m high, or those required to support surcharge loads or sloping
        backfill, will require engineer design and certification of construction. Retaining wall design should be
        carried out in accordance with AS4678-2002 Earth retaining structures.
        Design for temporary and permanent retaining structures could be carried out using a pressure
        distribution applicable to the wall type and based on the parameters listed in Table 6. These values do
        not include allowance for hydrostatic pressures, backslopes (assumed to be horizontal), nor transient (e.g.
        construction) or adjacent footing loadings.

        Table 6: Retaining Structure Design Parameters
                                                                             Lateral earth pressure coefficients
                                 Unit weight                                 Ka                    Ko              Kp
          Retained material                          Friction angle (°)
                                 (kN/m3)                                     (Cantilever wall)     (Non-yielding
                                                                                                   wall)

          Very Loose/Loose
                                        17                   27                     0.38                  0.55          2.66
          Sands

          Medium Dense
                                        18                   34                     0.28                  0.44          3.54
          Sands

          Dense (or Denser)
                                        19                   36                     0.26                  0.41          3.85
          Sands

          Future Controlled
                                         *                    *                       *                     *            *
          Fill*

        Note:     * Depends on fill material type and level of compaction.

        Retaining structures must be founded as per the recommendations in Section 6.2.2 above with the
        footings also designed to account for lateral loads imposed by the retaining wall. Detailed design must
        include an assessment of internal and global stability.



        Geotechnical investigation
        19 November 2025 | 25289-001-Rev0                                                                                      21
Document Set ID: 24631529
Version: 1, Version Date: 24/03/2026