RFI - Attachment C - Slope Stability Assessment and Geotechnical report · MCU20/0026

Project No. 1-22543                                                                                                          Page | 24
June, 2020
Ref: 1-22543, 2020-05-20, BR SSA VER 1
Sanya Holdings – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 40 Park Crescent, Sunshine Beach




            neighbouring properties and road. Given that the excavation is expected to be up to
            5m deep overall, a braced retaining wall will be required. This retaining wall should be
            installed prior to excavation to ensure stability of the sand profile.
            Several types of retaining walls could be employed including steel sheet piles,
            contiguous CFA piles or diaphragm wall. Each of these have relative advantages and
            disadvantages (technical and economic) which are best evaluated at the detailed
            design/tender stage.

Once the preferred retention option for the site boundaries has been selected, SSE should be
contacted to provide further design detail (if required).

    6.4 Retaining Walls

           6.4.1       General

It is understood that retaining walls will be required for parts of the site. The lateral earth
pressure distribution that affects the retaining walls on the site will depend upon the following
parameters:-

          In-situ and backfill material properties
          Design water regime at the rear of the wall
          Wall and cut geometry
          Surcharges affecting the wall
          Wall type
          The structural bracing of the wall and the timing of backfilling behind the wall

           6.4.2       Pressure Distribution

The following situations should be considered:-

          For cantilever walls, which allow some movement at the top, (i.e. at least 0.005H in
           clays) the active case (Ka) applies with a triangular distribution in both the short and
           long term situations.
          For cantilever walls which cannot tolerate this movement, the at rest case (Ko) applies
           with a triangular distribution in both the short and long term situations.
          For structurally braced walls the wall design should be checked for both a trapezoidal
           (clay soils - short term conditions) and triangular distribution with Ko values (long term
           conditions).

The pressure distributions as referred to above are shown in Figures 5 and 6. The parameters
selected for use in the figures are dependent on the preconstruction geometry of the face being
retained. It is expected that without battering, the earth parameters will control.

The lateral pressure distributions shown in Figures 5 and 6 include hydrostatic pressure and
show typical pressure distributions due to surcharge loadings. It is recommended that where
the retaining walls are expected to be surcharged (e.g. by footings, traffic loads, sloping ground
surface, etc.) Soil Surveys Engineering should be contacted to provide a recommended lateral
earth pressure distribution.




                                                                                                               SOIL SURVEYS