Geotechnical Report

                              PROPOSED UNIT DEVELOPMENT
                              31 BOTTLEBRUSH AVENUE, NOOSA HEADS

exposures or confirmation of foundations via certified building plans be undertaken to assess the possibility
of undermining. If undermining is a potential issue the existing structures may need to be underpinned or
excavations may require temporary shoring.
The advice of a suitably qualified and experienced RPEQ structural engineer must be sought regarding any
potential undermining and design and construction of any underpins/temporary shoring (if required).

The above recommendations do not supersede any existing safety regulations or legislation applicable to
excavations (e.g. limits on personnel entry into trenches).

Due to the highly permeable nature of the sands at this site, stormwater is expected to rapidly infiltrate the
ground, making un-sealed surface drainage ineffective for the control of flows. Any sealed areas should be
graded to ensure free drainage of stormwater away from construction areas, and to a control point(s).

 6.2.3       Filling
The existing sandy soils (fill and natural) where free of deleterious materials (e.g. vegetation, building debris
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
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 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
Based on the results of the investigation, the natural soil profile is non-reactive and so would be estimated to
have characteristic surface movements (‘ys’) of less than 20 mm (equivalent to Class S based on the reactivity
of the foundations assessed in accordance with AS 2870-2011 Residential Slabs and Footings).

It should be noted that the predicted order of movement is based on the existing soil profiles (i.e. no additional
cutting or filling), and moisture content changes within soils due to normal seasonal moisture variations only.

 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 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 of 1.2 m to 1.4 m BGL in the boreholes. Thus, piled
footings will be required unless excavations expose such materials at or near foundation subgrade level.




17 December 2020
Report No. 20370-001-Rev0                               11