geotech

                              PROPOSED UNIT DEVELOPMENT
                              9 BOTTLEBRUSH AVENUE, NOOSA HEADS

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
if safe to do so) to achieve a dry density ratio of at least 98% of the maximum Dry Density Ratio (DDR),
based upon the Standard Compaction method, or a Dry Density Index of at least 75%.

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.

Fill embankment edges must be over-filled by 0.5 m (horizontally) and then trimmed back to well compacted
material.

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 uncontrolled fill and poor bearing capacity soils at
shallow depths. However, 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 slab, footing 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, 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 below depths between 1.6 m and 2.2 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. 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 considered to be a suitable
foundation type for the proposed unit development generally. However, in areas of cut exposing medium
dense (or denser) sands at the subgrade level conventional high-level footings may be adopted. It should be
noted that excavation for concrete strip footings (or similar) may loosen the base. Therefore, the use of a
vibrating plate would be required to densify any high-level footing bases prior to the placement of reinforcing
steel.


13 July 2021
Report No. 21169-001-Rev0                               11