Slope Stability Report - Site 2

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•    Earthworks quality testing will be required on this site. The GTA will need to provide
     supervision in accordance with AS3798 and undertake field density tests to monitor the
     actual dry density and moisture content of placed materials.
•    Completed platforms should be sealed with a minimum 250 mm layer of relatively
     granular material (CBR15% or greater) to minimise the effects of relatively clayey
     subgrades drying out leading to excessive cracking.
•    Earthworks activities should be undertaken in relatively homogenous sequences where
     achievable (ie. do not place “pockets” of gravel material next to impermeable clays as this
     will lead to zones where water could become trapped).
•    Fill material will be subject to potential settlement post placement. Well compacted fill
     placed in accordance with AS3798 and otherwise, good earthworks procedure should
     typically be subject to settlement in the order of 0.5% to 1.0% of the fill thickness over a
     log cycle of time.

Arcos can assist in preparing earthworks documentation or guidelines for contractors to
adhere to in order to achieve an efficient and “fit for purpose” end product.


8.2 Retaining Structures
Retaining walls must be designed by a suitably qualified and experienced engineer and
preferably in accordance with AS 4678. The geotechnical parameters for use in design of either
flexible or rigid wall systems are presented in Table 2.


Passive forces should be ignored in areas where disturbance may occur (ie. future trenching
or earthworks processes). Compaction for retaining wall backfill should be undertaken with
due care. Layers should be placed thinner than for normal earthworks processes (say a
maximum layer thickness of 100 mm) and compacted using light weight equipment such as
hand controlled compactive equipment to minimise the stresses on the wall. If hand controlled
equipment is not practical, temporary wall propping will be required.


Walls will need to incorporate full height drainage in accordance with good design practice to
minimise hydrostatic pressure. The below parameters do not include surcharge loadings.


Table 2: Retaining Wall Parameters (Unfactored)
                                                Unit Weight        Friction Angle          Drained Cohesion
                 Material
                                                 (kN/m3)                 (Ø)                     (c’)

               Loose Sands                           18                   28                             0
              Very Stiff Clays                       19                   26                             3
              Weathered Rock                         21                   32                            10
Notes:   *-       Compacted under Level 1 conditions and behaves as clayey material

30 Nov 2020                                                                     Geotechnical Investigation