Approved Plans & Document EXE22-0020 · EXE22/0020

Specialists in transport geotechnics

   •    Subsurface drainage must be installed behind retaining walls in order to prevent the
        development of hydrostatic pressure. This normally comprises slotted ‘aggi’ pipe wrapped
        in filter ‘sock’ and placed in gravel backfill.
   •    Discharge from rainwater tanks, roof water and runoff collection systems must be
        controlled and discharged as diffuse flow at least 10 metres down slope of any footing,
        batter or retaining structure.
   •    Any water disposal must be controlled and discharged as diffuse flow at least 10 metres
        down slope of any footing, batter or retaining wall.
   •    All excess stormwater collected from proposed pavements (driveways/road) and around
        the proposed shed (including overflow from rainwater tanks) must be directed by pipes or
        lined channels to the legal point of downstream discharge.

6.4 Earthworks
The following recommendations are made for earthworks on the site:
    •   Vegetation acts to reinforce and protect the soil profile on a sloping site. Therefore,
        vegetation clearance should be kept to the minimum necessary to undertake the works
        and should be limited to the immediate vicinity of the building envelope and works area.
    •   Earthworks on the site should be minimised as far as possible.
    •   Any fill should be placed under a Level 1 Inspection and Testing regime in accordance
        with the requirements of AS3798-2007 “Guidelines on Earthworks for Commercial and
        Residential Developments” and certified by a geotechnical inspection and testing
        authority.
    •   Where fill is placed over side slopes, the subgrade slopes should be cut to form a series
        of horizontal terraces to ensure that the fill is bonded to the subgrade.
    •   Cut and fill batters must not exceed a slope of 2H:1V.
    •   All cut and fill earthworks of greater than 1.0 m height or depth must be designed by a
        professional engineer and checked for stability.
    •   All retaining structures greater than 1.0 m high must be designed by a professional
        engineer in accordance with AS4678-2002 “Earth Retaining Structures”. The design
        should be adequately designed for earth pressures, surcharges and elevated ground
        water conditions and fully account for sloped backfill and retained ground. The adopted
        design should also include conservatively sized drainage and regularly scheduled
        maintenance measures. Retaining walls should be founded into hard residual soils or
        weathered rock. The actual required depth of founding will need to be designed to
        provide an adequate factor of safety against global instability for the height of retained
        material.
    •   Earthworks should only be undertaken during periods when ground conditions are
        relatively dry and there is no threat of prolonged rainfall. A risk assessment should be
        undertaken prior to undertaking any earthworks operations on the site.




9 August 2022                     CGC-SR-2022-012-R01-Rev01                               Page 15