RFI - 21370-001-Rev1 66 Seaview Tce

                              PROPOSED RESIDENCE
                              66 SEAVIEW TERRACE, SUNSHINE BEACH

Site drainage should be designed to readily remove surface water and to prevent ponding of water on
subgrade areas during construction and also adjacent to foundations and perimeter slabs once construction
is completed.
It is recommended that footings be inspected by a suitably qualified and experienced engineer prior to
placement of steel reinforcement and pouring of concrete to confirm allowable bearing pressures and
cleanliness of excavations (depending on foundation methodologies).

If any soil conditions encountered during construction are found to differ from those noted in the geotechnical
investigation, Tectonic should be notified immediately and an inspection carried out to determine if changes
to footing design are required.

6.3       Temporary and Permanent Retention
Excavations are expected to range up to around 3.5 m BGL (existing ground levels) and, given that the
planned excavation extends close to some of the site boundaries and underground infrastructure (e.g.
underground services), and will interact with the existing road embankment alongside Seaview Terrace,
some form of temporary shoring will likely be required.

Based upon our experience with similar sites, we anticipate that temporary shoring may be achieved by use
of sheet piles, however Unitywater requirements for their infrastructure may restrict the use of sheet piles.
Shoring of deeper cuts would likely require lateral restraint, and this is conventionally achieved by helical
steel anchors (similar to screw piles). However, the proximity to neighbouring properties and the road
corridor would require permissions to be obtained for subterranean access. Therefore, where lateral support
by cantilever only is not feasible, it is suggested that internal struts/propping be considered to provide lateral
restraint for the shoring system.

Anchored or propped sheet piles may require pre-drilling to prevent adverse vibrations during sheet pile
installation.

Other shoring methods that could be considered include bored contiguous or secant piles. Non-contiguous
or soldier pile walls are not feasible for the proposed development due to the likelihood that loose sands
would ‘flow’ through gaps between the piles.

An advantage of contiguous or secant pile wall retention systems is that they are ultimately used for the
permanent walls, whereas sheet piles would be temporary to provide retention during construction only,
therefore requiring a permanent structural wall to be constructed. Bored pile walls generally require greater
width (horizontally) for installation as compared to sheet piles and are often more expensive.

The advice of a specialist shoring contractor must be sought regarding feasibility, design and installation of
the proposed retention system. It will be necessary to conduct numerical analysis to optimise the retention
system. Detailed design will also need to account for relevant factors of safety to maintain the temporary
and long-term stability of the retention system.

Retaining structures greater than 1 m high, or those required to support surcharge loads or sloping backfill,
will require engineer design and certification of construction. Retaining wall design should be carried out in
accordance with AS4678-2002 Earth retaining structures.

Design for temporary and permanent retaining structures could be carried out using a pressure distribution
applicable to the wall type and based on the parameters listed in Table 6 overleaf. These values do not
include allowance for hydrostatic pressures, backslopes (assumed to be horizontal), nor transient (e.g.
construction) or adjacent footing loadings.




28 April 2022
Report No. 21370-001-Rev1                               19