Att 9 - Geotech and PASS report

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8.     Comments

8.1    Site Preparation and Earthworks

It is recommended that the following site preparation and earthworks procedures be carried out where
the proposed development will consist of new filling, slab-on-ground construction and/or pavement
construction:
     Any deleterious, soft, wet or highly compressible material or topsoil material rich in organics or
      root matter should be stripped and removed.
     The silty and clayey sands will likely be very sensitive to water and will lose strength if they
      become wet prior to or during construction. This may require the installation of subsurface drains
      to intercept seepage and facilitate drying out should construction commence during or following
      an extended period of wet weather. Significant works to ‘bridge’ these soils using overburden
      material, or similar, would be required if weather conditions are unfavourable.
     Undertake a minimum of six passes of the stripped surface using a smooth drum roller with a
      minimum static weight of 12-tonne to detect the presence of any soft or loose spots. Vibration
      must not be used as the compaction process may cause the groundwater to rise due to capillary
      action. Areas demonstrating excessive movement under test rolling should be either tyned, dried
      and recompacted or removed and replaced with compacted select filling. Treatment should be to
      a standard sufficient so that the subgrade passes test rolling and that compaction can be
      achieved in the first layer of filling. All earthworks should be carried out in accordance with AS
      3798-2007 (Ref 5).
     Depressions formed by the removal of existing structures, pavements, underground elements etc.
      will require all disturbed, weakened soils to be excavated out and then backfilled with compacted
      select filling.
     It is considered that the majority of materials won from excavations on site where free of organic
      and deleterious material will generally be suitable for reuse as bulk filling provided the moisture
      content of the soils on placement approximates the OMC. This may require moisture conditioning,
      especially where material has been stockpiled for extended periods or is significantly wetter than
      OMC.
     Imported select filling material, if required, should be a good quality select filling material with
      minimum soaked CBR of 10%, of low plasticity and well graded with a maximum particle size of
      75 mm.
     Where clay soils are proposed to be used as filling beneath structures, such use is contingent
      upon potential reactive movements being tolerable and a reduced CBR strength. It is
      recommended that cohesive material be placed at depth and granular material (if available) be
      placed close to footing level. This will reduce the effects of seasonal moisture change and
      foundation soil reactivity, and will improve surface trafficability.
     Approved structural filling should be placed in layers not exceeding 0.2 m ‘loose’ thickness, with
      each layer compacted to a minimum dry density ratio of 98% relative to Standard compaction.
      Where filling has a significant clay content, moisture content within the filling should be
      maintained within 2% of OMC during and after compaction.




Geotechnical Investigation, Proposed Commercial Development                             90151.00.R.001.docx
11-19 Hilton Terrace, Tewantin                                                                    May 2017