RFI - 21370-001-Rev1 66 Seaview Tce

                              PROPOSED RESIDENCE
                              66 SEAVIEW TERRACE, SUNSHINE BEACH

6.1.3       Filling
The natural sandy soils where free of deleterious materials (e.g. vegetation, excessive rootlets/organics etc.)
may be reused as structural fill (retained under the building), 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

The primary recommendation would be to re-use site won material, or use a similar granular soil where
import is required. In compliance with above, cohesive soils may be tolerated, however their use should be
limited to lower layers in fill (at least 1 m below surface), and impacts on site classification (Ref. Section
6.2.1) must be assessed by designers.

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 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.

6.2       Building Foundations
6.2.1       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.

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, footing and plumbing design.

6.2.2       Footing Design
No design loadings were available at the time of reporting. Footings for the proposed residence 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 1 m into medium dense to dense (or denser)
natural sands. High-level footings may be possible in areas of deeper excavation where medium dense to
dense (or denser) sands are exposed at or near the subgrade. This would be subject to an assessment by a
suitably qualified and experienced RPEQ geotechnical engineer. High-level footings, so founded, could be
designed using a maximum allowable bearing pressure of 100 kPa.
Elsewhere (excluding pile wall), based on the results of the investigation, pile founding depths of about 2.5 m
to 3 m BGL (existing ground levels) are anticipated. Deeper pile depths may be necessary subject to
assessment of building loads at the detailed design stage.

Steel screw piles are considered to be a suitable foundation option. Piles so founded may be designed using
an allowable end bearing pressure of 1 MPa. Due to the presence of very loose to loose upper sands,
together with the restricted site conditions and close proximity of adjacent houses, open bored piers or driven

28 April 2022
Report No. 21370-001-Rev1                                17