Reference Document - MCU26 0001 & OPW26 0002 - AS PUBLISHED · MCU26/0001

        Table 4: Retaining Structure Design Parameters

                                            Unit                                          Lateral earth pressure coefficients
                                                         Friction
          Retained material                weight                                   Ka                       Ko                 Kp
                                                         angle (°)
                                          (kN/m3)                            (Cantilever wall)       (Non-yielding wall)


                  Loose Sands                17             27                     0.38                      0.55               2.66


             Medium Dense Sands              18             33                     0.29                      0.46               3.39


            Dense (or Denser) Sands          19             36                     0.26                      0.41               3.85


             Future Controlled Fill*          *              *                      *                          *                 *


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

        Retaining structures must be founded as per the recommendations in Section 6.3.2 above with the piled
        footings, if required, also designed to resist lateral loads imposed by the retaining wall. Detailed design
        must include an assessment of internal and global stability.


        6.5             Drainage
        Permanent surface diversion drainage should be constructed above the crest of any new cut or fill
        embankment or retaining walls (e.g. grassed or landscaped swales or diversion mounds). Adequate site
        drainage must be installed to ensure that stormwater runoff is directed away from building walls,
        footings, batters and retaining walls.
        Although unlikely, if groundwater seepage is encountered during excavations, Tectonic must be notified
        to assess the impact on stability.
        Subsurface drainage must be installed behind any retaining walls (e.g. slotted ‘aggi’ pipe wrapped in
        filter ‘sock’ placed in gravel backfill). Depending on matters such as the extent of drainage installed and
        site-specific groundwater conditions, the designer must make an assessment of hydrostatic pressure to
        be accounted for in the design of the retaining structure.
        All excess stormwater collected around the building (including overflow from rainwater tanks, etc.) must
        be directed by pipes or lined channels to discharge into the existing stormwater infrastructure along
        Bottlebrush Avenue. Subsurface disposal of stormwater must not be undertaken.



        7.              Conclusion
        Based on the findings of our assessment it is assessed that there would be a Low Risk of slope instability
        affecting the proposed development subject to implementation of the recommendations given in this
        report.




        Geotechnical Investigation
        30 January 2026 | 25408-001-Rev0                                                                                               16
Document Set ID: 25158026
                  24528612
Version: 1,
         2, Version Date: 10/09/2026
                          13/02/2026