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

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