SUPERSEDED Reference Document

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6.4    Foundations

The subsurface conditions encountered in the bores typically comprised relatively loose to
medium dense sand fill, overlying typically medium dense to dense natural sand. At basement
level, high level footings are expected to be founding into medium dense or better sand.

High level footings may be designed using the allowable bearing pressures given in Table 4.

Table 4: Allowable Bearing Pressures for High Level Footings
 Material                                                   Allowable Bearing Pressure (kPa)
 Existing uncontrolled fill                                 75
 Medium dense (or better) natural sand                      100

The above bearing pressures are contingent upon all footing excavations being free of any loose
material prior to the placement of concrete. All footing excavations should be inspected and
tested by an experienced geotechnical engineer from Douglas to confirm bearing capacity prior
to casting of concrete.

Experience indicates that properly designed and constructed high level footings sized using the
above allowable bearing pressures are likely to undergo settlements in the order of 1% of the
footing width. Further advice should be sought from Douglas regarding settlements once actual
footing configurations and design loads are known.

Slabs supported on high level footings should be stiffened to suit the expected ground surface
movements.

Where footings are located adjacent to underground services, the footings should extend to
below invert level for a distance of 1 m out from the trench. Beyond 1 m from the trench, the
footings should be taken to below an imaginary line drawn up at 45 degrees from the invert level.
These requirements do not override minimum structural footing base levels. Where necessary,
footings may be made up with mass concrete poured to the underside of footing, or alternatively
constructed over excavated pedestals.

Alternatively, where development loads exceed the above allowable bearing pressure and
estimated settlements, a suitable deep foundation will be required. Screw piles would be
considered suitable given the subsurface conditions encountered.

The ultimate, unfactored end bearing values given in Table 5 will need to be multiplied by a
suitable geotechnical strength reduction factor (Øg) to obtain the design geotechnical strength
(Rd,g) of piles. In accordance with AS2159 (2009), the Øg value must be determined by the designer,
but based on the anticipated site, design and installation risk factors, a Ø g value of at least 0.45 is
considered likely for a low redundancy pile system.




Proposed Residence                                                                    229073.00.R.001.Rev0
13 Mermaid Quay, Noosaville                                                                     June 2024