Sealed Judgement Neate 1219 of 2020 · MCU18/0015

      of safety against instability and the landslide risk to life and property is assessed as
      ‘Low’ when considering the AGS ‘Landslide Risk Management Guidelines 2007’.

3.0 THE WEIGHT AND FOOTPRINT PRESSURE OF THE EQUIPMENT TO BE
     USED AND CONSTRUCTION SEQUENCE
With respect to the construction sequencing and considering the sequence proposed in
Attachment C to the SJER, we make the following comments and recommendations. Numbers
relate to each Stage presented in Attachment C:-

   1. Vegetation Strip, Excavator 10-15 tonne.
   2. Installation of sheet piles by high frequency vibration with head mounted on 20 tonne
      (max.) excavator. Excavator track pressure 40kPa. Footprint pressure 15kPa.
   3. Progressive excavation following placement of sheetpiles, by excavator 10-15 tonnes.
      Track pressure approx. 35-40kPa. Footprint pressure approximately 15kPa.
      Preparation of access track for piling equipment to be totally in cut, i.e., no fill on
      eastern side of access track. Material excavated to be removed from site. No
      stockpiling on site at this stage.
   4. Piling to retaining wall.
      Propose excavator (30 tonne) mounted CFA piling rig acting in pendulum fashion.
      Track pressure 50-55kPa. Footprint pressure 20kPa.
      Rig to sit totally on natural cut material with minimum 0.5m edge clearance to outer
      edge of access track.
      Piling to be undertaken progressively downhill in front of piling rig, i.e. rig to have
      completed piles on downhill side of rig.
      Stability analyses show critical shallow slip surfaces in the natural profile not extending
      below the piling rig, i.e., “non worsening impact on slope stability” (refer Figure 1).
      Additional piling to retaining structures extending beyond the access road retaining
      wall that can be reached by the piling rig from the access road should also be
      considered at this stage.
   5. Construct Retaining Wall
      This will be undertaken progressively as piling continues down site to the north.
      No filling to be placed until retaining wall complete.
      Wall design to consider both construction surcharge loadings and long-term loadings.
   6. Excavate access for piling rig to lower level. Initial excavation to be undertaken by
      excavator sitting above access road retaining wall.
      5-10 tonne excavator to be used at lower level. Track pressure 35-40kPa, Footprint
      pressure 10-15kPa.
      Double handling of excavated soil will be required. Soil may be locally stockpiled above
      the access road retaining wall to allow for local backfilling. Retaining wall design to
      consider any fill surcharge loads.
   7. Piling to lower retaining wall.
      As for Step 4, the piling rig must sit totally in cut. Access to this area will be limited
      with the piling rig to be running parallel to upper retaining wall. Stability analyses
      indicate that use of a 30 tonne rig cannot be considered at this level as the critical slip
      circle extends beneath the outside track resulting in a lower factor of safety than the
      natural profile. Use of steel plate piling mat to distribute loads to below a footprint load
      of 20kPa will be required at this level. Refer Figures 2 and 3. Alternatively, a small rig




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