20220109 - Geotech · OPW23/0182

                             PROPOSED RESIDENCE
                             21 MAHER TERRACE, SUNSHINE BEACH

 6.3.3       Filling
Excluding topsoil and any over-wet soils, the existing soils where free of deleterious materials (e.g.
vegetation, cobbles/boulders etc.) are expected to be suitable for re-use as structural fill, subject to
appropriate moisture adjustment. Due to the mostly highly plastic and potentially highly reactive nature of
the clays encountered, careful handling and placement would be required when reusing the site won clays,
with adverse impacts due to potential high shrink-swell to be considered (particularly for pavement and
building design).

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.

6.4       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.
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 M, with the
estimated characteristic surface movements (‘ys’) ranging up to about 40 mm. A site classification of Class M
is recommended in relation to assessment of flexibility requirements for ground slab, footing and plumbing
design.

It should be noted that placement of highly reactive clay fill may have an adverse impact on the site
classification (i.e. Class H1 or higher).

6.4.2       Footing Design
Given the excavation depths and based on the results of the borehole drilling, stiff/medium dense (or
stronger) residual soils and possibly XW materials are expected to be exposed across the basement floor
level. In areas of shallower proposed excavations, weaker foundations may be present at subgrade level. It
is recommended that a uniform foundation is adopted across the entire building footprint to reduce
differential settlements.

Depending on the design loads, high level strip and pad footings, or a stiffened raft slab, may be adopted for
the proposed basement and development. An allowable bearing pressure (ABP) of 100 kPa may be
adopted for high level footing design where footings are founded in stiff/medium dense (or stronger) residual
soils.




16 July 2021
Report No. 21236-001-Rev0                              13