ECM_22343520_v1_Geotechnical Investigation · 132000.200173.1

                                             PROPOSED RENOVATIONS
                                             2 ARAKOON CRESCENT, SUNSHINE BEACH

            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 trapezoidal (for
            propped or anchored walls) pressure distribution applicable to the wall type and based on the parameters
            listed in Table 3. These values do not include allowance for hydrostatic pressures, backslopes (assumed to
            be horizontal), nor transient (e.g. construction) or adjacent footing loadings.
            Table 3: Retaining Structure Design Parameters
                                                                                  Lateral earth pressure coefficients
                                           Unit
                                                      Friction
              Retained material           weight
                                                      angle (°)            Ka                        Ko
                                          (t/m3)                                                                        Kp
                                                                    (Cantilever wall)        (Non-yielding wall)

              Very Loose/ Loose
                                            1.8           27               0.38                     0.55                2.66
              Sands


              Medium Dense Sands            1.9           34               0.28                     0.44                3.54


              Dense (or Denser)
                                            1.9           36               0.26                     0.41                3.85
              Sands


              Future Controlled Fill*        *            *                   *                       *                  *

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

            As a minimum, 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, together with required bearing capacity and
            founding depth, by the retaining wall design engineer.

            6.4         Drainage
            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. It is assumed that the pool floor will include a
            hydrostatic pressure relief valve. The outlet pipe from this valve must be taken to ‘daylight’ at the ground
            surface.
            All collected roof water should be directed by pipes to the council stormwater system along The Esplanade
            (e.g. through the use of a ‘wet’ or ‘charged’ drainage system) or, where not physically possible, surface
            water should be directed to infiltrate into the ground around the edges of hard surfaces, with infiltration
            areas set back as far as possible from the crest of the dune slope. Hydraulic design should be such that
            under no circumstances are uncontrolled stormwater flows permitted over the dune face; where channelised
            erosion and scour features could develop.



             24 February 2023
             Report No. 22484-001-Rev0                                   18
Document Set ID: 22343520
Version: 1, Version Date: 16/03/2023