Geotechnical Investigation

                              PROPOSED CALILE HOTEL NOOSA DEVELOPMENT
                              3 – 7 SERENITY CLOSE, NOOSA HEADS

6.3       Building Foundations
6.3.1       Indicative Site Classification
Site classifications for footing design are determined in accordance with AS 2870-2011 Residential Slabs and
Footings, and depend on the depth of cut / fill undertaken at a site, variations in the natural soil/rock depths,
and the reactivity of the in situ soil / rock and any imported fill materials. It should be noted that the proposed
works are outside of the scope of AS2870.

Based on the results of the investigation, the site is classified as Class P in accordance with AS 2870-2011
Residential Slabs and Footings, due to the presence of poor bearing capacity soils at shallow depths,
uncontrolled fill and trees. If not for these factors, the site would have the characteristics of Class S, with the
estimated characteristic surface movements (‘ys’) ranging up to about 20 mm. However, due to the potential
variability in subgrade density a site classification of Class M is recommended in relation to assessment of
flexibility requirements for ground slabs, footings and plumbing design.

6.3.2       Footing Design
No design loadings were available at the time of reporting. Footings for the proposed development and any
ancillary structures (e.g. retaining walls, pool etc.) must penetrate through any unsuitable soils or fill (i.e. very
loose to loose sands) to found at least 0.5 m into medium dense (or denser) natural sands or future granular
controlled fill. Medium dense natural materials were encountered from depths of between 0.4 m and 1.2 m
BGL (existing ground levels) in the boreholes and DCPs.

Based on the anticipated excavation depths, such materials are generally anticipated to be at or near the
design subgrade level. Where medium dense (or denser) sands are not present at the subgrade level, over-
excavation and re-compaction of the loose materials as outlined in Section 6.2.3 could be undertaken to
achieve a medium dense (or denser) foundation subgrade. High level footings, where achievable, may be
designed using an allowable bearing pressure of 200 kPa, provided that they are founded in the natural
medium dense (or denser) sands or Level 1 granular fill as outlined above. A suitably qualified and
experienced geotechnical RPEQ must carry out inspections and testing of the foundations during construction
to confirm the allowable bearing pressures. Settlement under such loads is expected to be in the order of up
to 20 mm or 1% of footing width; however, detailed settlement analysis should be undertaken following
confirmation of building loads.

In general, it should be noted that excavations for concrete strip/pad footings (or similar) may loosen the
base. Therefore, the use of a vibrating plate with ample water would be required to densify any high-level
footing bases prior to the placement of reinforcing steel.

Where high-level footings cannot be achieved (e.g. adjacent to existing retaining walls, in areas of deeper
loose soil/future fill) piled footings will be required. Due to the presence of loose sands and nearby
structures, open bored piers or driven piles are not recommended for this site and it is expected that steel
screw piles could be utilised. Steel reinforced concrete bored piles may be possible; however, the use of
sacrificial liners (e.g. Formatube) would be required. Piles founded at least 1 m into medium dense (or
denser) sands may be designed using an allowable end bearing pressure of 300 kPa, or 1 MPa if founded in
dense sands at about 4 m to 6 m BGL (existing ground levels).

The advice of a specialist piling contractor must be sought regarding feasibility, design and installation of any
piling system for this site, including an assessment of potential vibration effects on nearby structures, and
monitoring requirements.
If steel screw piles are adopted, it will be important to ensure close supervision of installation, as piling may
not encounter sufficient drilling resistance (from torque measurement) in sands at the suggested founding
depth, and piles could extend to much greater depth than necessary.

It is therefore recommended that site specific static load testing be conducted from screw piles, if adopted, at
a minimum. Where tension or compression capacity developed in the footings is critical for the future
structure (e.g. resistance to uplift forces from high winds), then cyclic load tests (including measurement of
deflections under tension and compression cycles) should also be undertaken prior to construction.
Kentledge for static testing, or simulated cyclic loads, should prove the piles to a minimum of two times the
expected working load within tolerable deflections.

7 October 2022
Report No. 22239-001-Rev0                                16