Geotech

                              PROPOSED UNIT DEVELOPMENT
                              27 BOTTLEBRUSH AVENUE, NOOSA HEADS

6.3.3       Filling
The natural sandy soils where free of deleterious materials (e.g. vegetation, organics etc.) may be reused as
structural fill, subject to appropriate moisture adjustment. It should be noted that compaction of such
relatively ‘clean’ sands as structural fill requires the addition of substantial volumes of water (‘flooding’)
combined with the use of vibratory compaction equipment (typically a smooth drum roller or heavy vibrating
plate).

Should importation of fill be required, it is recommended that such fill should comply with the following:

       Minimum CBR of 10%
       Maximum plasticity index of 15%
       Shrink-swell index ≤ 1%
       Maximum particle size of 100 mm

Any fill should be compacted at moisture contents within the range of ±2% of optimum moisture content for
Standard Compaction. Fill material should be placed in 250 mm thick (loose thickness) layers and be
compacted by repeated rolling using a minimum 4 tonne smooth drum roller (or equivalent, with vibration on




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if safe to do so) to achieve a dry density ratio of at least 95% of the maximum Dry Density Ratio (DDR),
based upon the Standard Compaction method, or a Dry Density Index of at least 70%.

Confirmatory compaction testing must be carried out at regular intervals. A minimum of two tests per vertical
lift is recommended where structural fill heights are to exceed 300 mm. Further details for control and testing
of fill are given in Australian Standard AS 3798-2007 Guidelines on Earthworks for Commercial and
Residential Developments.
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Fill embankment edges must be over-filled by 0.5 m (horizontally) and then trimmed back to well compacted
material.

6.4       Building Foundations
6.4.1       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
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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
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variability in subgrade density a site classification of Class M is recommended in relation to assessment of
flexibility requirements for ground slabs, footing and plumbing design.

6.4.2       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, etc.) must penetrate through any fill materials and unsuitable natural
soils (i.e. very loose to loose sands) to found at least 0.5 m into medium dense (or denser) natural sands.
Such materials were encountered from depths of between 2.2 m and 5.2 m BGL (existing ground levels) in the
boreholes. Thus, piled footings will be required unless excavations expose such materials at or near
foundation subgrade level.

Piles so founded may be designed using an allowable end bearing pressure of 300 kPa, or 1 MPa if founded
in dense sands at about 5 m to 6 m BGL. High level footings, where achievable in deeper cut areas, may be
designed using an allowable bearing pressure of 100 kPa provided that they are founded in the natural
medium dense (or denser) sands. Settlement under such loads is expected to be in the order of up to 20 mm
or 1% of footing width.

Given the sandy soil profile and depths of footings required, steel screw piles are an appropriate footing type
for the proposed development generally. However, in areas of cut exposing medium dense (or denser)


10 November 2021
Report No. 21286-001-Rev0                                11