Reference document Geotech Investigation · MCU22/0087.01

                                             PROPOSED UNIT DEVELOPMENT
                                             37 BOTTLEBRUSH AVENUE, NOOSA HEADS

            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 (e.g. trapezoidal for propped or anchored walls) and based on the parameters
            listed in Table 4. These values do not include allowance for hydrostatic pressures nor transient (e.g.
            construction) or adjacent footing loadings.
            Table 4: 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           28               0.36                     0.53                2.77
              Sands


              Medium Dense (or
                                            1.9           34               0.28                     0.44                3.54
              Denser) 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 6.3.2 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 stability. A solution using screw piles to support retaining walls, possibly including
            raked piles, may be feasible although bending and shear capacities would need to be carefully checked in
            design from a soil-structure interaction viewpoint. Additional lateral capacity may be achieved by
            incorporating a deeper pile cap that also acts as a shear key attracting passive resistance in the sands in front
            of the wall.

            6.5         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.
            All excess stormwater collected around the residence (including overflow from rainwater tanks etc.) must be
            directed by pipes or lined channels to discharge into the existing stormwater infrastructure along Bottlebrush
            Avenue or Berrima Row. Subsurface disposal of stormwater must not be undertaken.




             13 May 2022
             Report No. 22151-001-Rev0                                   14
Document Set ID: 22198682
Version: 1, Version Date: 05/12/2022