21054-001-Rev0 Tristania Dr

Peter Williams                                                                                 21054-001-Rev0
                                                                                              25 February 2021

Following clearing of vegetation, tree stumps and large roots must be ‘grubbed out’, with any organic rich
topsoil stripped from construction areas. Organic topsoils and garden soils must not be re-used as structural
fill, however they may be retained on site for later use across landscaping areas, if required. Sandy soils
where free of deleterious materials (e.g. vegetation, 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 vibrating plate). Care must be taken with the use of vibratory equipment to ensure that there are no
adverse impacts on surrounding structures. The impacts from ground vibration must be closely monitored
and managed during construction. It would be prudent to conduct a dilapidation survey of neighbouring
structures prior to commencement of construction.

The exposed natural subgrade following excavations will likely be in a loose condition and must be
compacted by several passes of a vibrating plate or minimum 4 tonne vibrating smooth drum roller, in
conjunction with surface application of ample water, to achieve the required compaction.

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.

Excavations should be achievable using conventional earthmoving plant (e.g. small to medium sized
excavators with toothed buckets).

Temporary cuts in the natural sands could be formed at 1V:1.H, for unsurcharged batters up to 2 m in height,
provided groundwater seepage is not encountered. Deeper cuts, if required, should be specifically assessed
by Tectonic. All fills, and permanent cuts exceeding 1 m, must be retained. Permanent cut batters up to 1 m
height shall not exceed 1V:2.5H. Any permanent soil and fill batters will require erosion protection (e.g.
revegetation or surface protection).

The above recommendations do not supersede any existing safety regulations or legislation applicable to
excavations (e.g. limits on personnel entry into trenches).
Any excavations required adjacent to existing structures will need to be specifically designed to ensure that
the structures are not adversely affected ('undermined').

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), prior
to off-site release.




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