Geotechnical Report

We recommend that all footings be founded into loose (or denser) natural sands. We expect that steel screw
piles or bored piles (with an allowance for sacrificial liners) formed using an auger attachment to an excavator
or hand auger techniques, depending on access constraints, would be required.

Lined hand drilled piles or steel screw piles (say 0.35m diameter) founded at a depth of least 2.0m or 4 pile
diameters (whichever is deeper) into loose (or denser) natural sands may be designed using an allowable end
bearing pressure of 250kPa.



6.6     Proposed Pool
The following earth pressure coefficients and subsoil parameters may be adopted for the design of the pool
walls:
     For the sections of pool walls formed below existing surface levels, we recommend the use of a triangular
      lateral earth pressure distribution with an ‘at rest’ earth pressure coefficient (ko) of 0.6 for the soil profile,
      assuming a horizontal backfill surface.
     A bulk unit weight of 21kN/m3 should be adopted for the retained profile.
     Any surcharge affecting the walls (e.g. nearby footings, compaction stresses, sloping retained surfaces,
      construction loads etc) should be allowed for in the design using the above earth pressure coefficient.

The pool base should be supported on piles founded in loose (or denser) natural sands in accordance with
the advice presented in Section 6.5 above.

The pool should be provided with a one-way or non-return valve at its lowest point so as to prevent buoyancy
in the event that external groundwater levels rise above the water level within the portions of the pool that
are below proposed surface levels, unless such groundwater could be fed into a gravity drain.

The pool backwash system should be piped and discharged to the main sewer system.



6.7     Floors and Deck Areas
We have assumed that the new timber floors and deck areas will be suspended between footings founded
in the loose (or denser) natural sands as outlined in Section 6.5 above.

If fill is proposed to be placed to raise site surface levels (not our preferences as effective compaction in such
a small and restricted site area would be difficult to achieve) then further geotechnical advice must be sought.



6.8     Sewer Pipeline Management
A Unitywater sewer pipeline orientated approximately north-west to south-east is present beyond the rear
boundary of the site. Unitywater’s online Infrastructure mapping indicates the invert levels of the main are
about RL8.81m to RL8.56m. Correlating this information with Noosa Council’s online Contour overlay maps,


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