SUPERSEDED Reference Document

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However, it is anticipated that the sand fill will be excavated and removed as part of the basement
excavation. Provided all footings (ie. edge beams, internal beams and load support thickenings)
extend through any fill and found into the natural strata, the site maybe be reclassified based on
engineering principles. Based on the investigation results, the existing sand fill and natural sand
material encountered on this site are non-reactive to changes in soil moisture content, consistent
with Class A conditions.

6.2    Basement Construction

Excavations in the order of 2.5 m below existing site levels are anticipated to achieve the proposed
basement level.

Based on the ground conditions encountered in the bores, excavation of the existing fill and
natural sand could be undertaken using conventional small to medium sized earthmoving
equipment, such as drotts, backhoes or 15t (or larger) excavators. The use of pneumatic tools or
hydraulic rock breakers will be required to assist in the excavation of any existing concrete.

It should be recognised that the excavatability estimates are based on materials encountered at
the bore locations only and that conditions may prove more difficult (or easier) for excavatability
beyond the bore locations and the depths drilled as part of this investigation. This information is
also based on past experience and reference to published literature and should only be taken as
a broad guide as many factors influence excavatability including plant condition and operator
expertise.

Where space permits, battering would be the most economic option to stabilise the excavation
faces. Temporary batter slopes in fully dewatered conditions should be no steeper than 2.5H:1V.
Battering is not likely to be suitable where there is a need to build close to the site boundaries
and adjacent to in-ground services or where excavations will extend below the groundwater
table.

It is therefore anticipated that bulk excavation will require positive support comprising temporary
measures such as sheet piles, or permanent measures such as secant or contiguous pile walls.

Sheet piles could either be installed to act as a cantilever or be anchored or propped. Anchoring
would allow the use of a lighter section sheet and would provide better control of soil movements.
These movements will be both lateral and vertical occurring at the crest of and behind the
excavated faces as a result of relaxation of these faces. The magnitude of settlement would be
dependent upon the sheet stiffness but would decrease with increasing distance from the
excavated face and be essentially zero about 3 m behind the wall.

A general drawback with sheet piling would be the ground vibrations caused during driving
which could cause settlement in any loose near surface sands. Where vibrations cannot be
controlled adequately, then the use of secant or contiguous pile walls may be required. The
advantage of a piled wall is that it could be incorporated into the final structure. As sandy soils are
mainly present on this site, it is envisaged that a secant pile will be required to prevent excessive
ground loss from between the piles which could occur with contiguous piles.

The design of flexible and rigid retaining walls could be undertaken using a triangular pressure
distribution and the earth pressure parameters given in Table 3. Flexible walls are those which
are free to rotate or tilt (such as cantilevered walls) and should be designed using active (Ka) earth




Proposed Residence                                                                   229073.00.R.001.Rev0
13 Mermaid Quay, Noosaville                                                                    June 2024