Reference Document - MCU25 0101 (As Published)

 Project No. PG-13872                                                                                           Page | 9
 August 2025
 Ref: PG-13872, 2025-08-14, GR VER 1
 Stephen & Jane Struss – Geotechnical Investigation - Proposed Residence, 28 Kingfisher Drive, Peregian Beach




  iii.     Excavate the site to the design basement level and test the base of the
           excavation to determine the extent of over-excavation required.

 iv.       Following determination of the required extent of over-excavation, excavate
           the site to the required level and compact the exposed sands using a large
           (300kg plus) vibrating plate compactor or a small smooth drum roller. It should
           be noted that the silty sands encountered at some test locations could be
           difficult to compact and manage, if not appropriately dewatered. It may be
           necessary to remove the silty sands and replace them with clean sands from
           higher in the excavation profile.

  v.       Replace the over-excavation with “clean” sand and compact in layers to the
           design founding level. The founding soils should be compacted to a minimum
           Density Index of 75% (in accordance with AS 1289 5.6.1).

Foundation Design Parameters

For footings founded between 2m and 4m below the ground level, an allowable
bearing capacity of 225kPa could be adopted, following confirmation that a
minimum Density Index of 75% is present for a minimum depth of 1m below the
footings.

If the exposed sands are disturbed or loosened during the excavation operation, they
should be recompacted. Consideration should be given to placing a 50mm thick
(minimum) concrete binding layer across the footings, immediately following
excavation.

Settlement Potential

Settlements from underlying improved sands and natural soils beneath a pad footing
of 2.5m width (i.e. maximum column load of 1500kN) at a nominal founding depth of
2m to 4m below existing ground level at a design bearing pressure of 225kPa have
been calculated to be in the order of 15mm with anticipated differential settlements
of between 25% and 50% of the calculated total settlement for pad footings founded
at a similar depth.

The settlement will occur as “immediate” settlement as the building loads are applied.

Hydrostatic Uplift Forces

For a fully tanked basement, hydrostatic uplift forces should be considered in the
design. It is recommended hydrostatic uplift forces in groundwater levels to at least
RL1.5 to 2.0 be taken into consideration on this site and checked for the Q100 flood
condition.