Geotechnical Investigation Report

footings. Any batters or excavations exceeding this should be inspected by a suitably qualified geotechnical
engineer to assess to the temporary stability of the batter; and

Batters exceeding the heights or slopes stated above, or batters that contain buildings or surcharge loads within
a distance equal to one batter height from the crest, should undergo detailed stability analysis to determine risk
levels.

If temporary batters steeper than 1.5H:1V are proposed for the site these will require the design of a suitable retention
system.

6.5 RETAINING WALL PARAMETERS

It is understood that retaining walls may be required for the development. Retaining wall type and height are unknown
at the time of writing this report.

Any temporary or permanent retaining structures at the site should be designed in accordance with AS4678-2002
‘Earth Retaining Structures’.

Based on the results of the fieldwork, retaining wall design parameters for temporary or permanent walls are
summarised in Table 4.

Table 4: Design parameters for temporary and permanent retaining walls

   

nee Coefficient of Melis oma)
, Dry unit weight ite earth NS oTT aks)
Material Type Angle
(kKN/m3) ne IRS Ceee| mike g modulus
. Co) (MPa)
Loose sand 7 28 0.53 2
Medium dense sand 18 34 0.43 6
Dense sand 19 39 0.36 10

Retaining wall design should consider the below:
The distance from the crest and magnitude of any surcharge loads (ie buildings, roads).
Whether the selected wall type is suitable for the proposed loading conditions.
Wall geometry and the presence of any slopes at the crest or toe of the wall.
Type of backfill to be used behind the wall, and whether compaction will exert additional forces onto the wall.

6.6 BASEMENT CONSTRUCTION CONSIDERATIONS

Based on the provided drawings, it is implied that a temporary soil retention system may be necessary for the
excavation and construction of the building’s basement level. Temporary retention options and considerations are as
follows:

A secant pile wall can be used, however it should be noted that standard piling tolerances might lead to the
formation of gaps within the wall, which could result in potential leakage issues.

Sheet piles may also be contemplated, taking into account the vibrations caused by their installation and the
challenges associated with reaching the required depths. The installation of sheet piles in loose sand can result in
movement and damage to adjacent assets such as services, pavements and structures. The impact of potential
ground movement, as well as noise and vibration, should be considered where f=driven or vibratory sheet piles
are being considered for ground retention.

It's important to recognise that some ground movement may occur behind retaining walls. The amount of
movement will depend on factors such as the height of the wall, the type of wall chosen, and the construction
methods used. These factors should be considered during the design and construction of the retaining walls to
ensure that surrounding facilities are not negatively impacted.