OPW052025 Report - Part 2

  Text Figure 15: Footing depth required to minimise the risk of undermining and surcharge loading

Footing bases must be cleaned following mechanical excavation to expose undisturbed materials over
the full base area. If the building design requires a socket into the underlying weathered basalt for some
of the footings, it would be essential that the contractor have suitably sized rock augers and downhole
breaking tools. Where bored piles are utilised, it is recommended that the piling contractor have a ‘mud
bucket’ or similar device to enable clean out of the pile bases. ‘Spinning’ of the augers is not acceptable
and will not sufficiently remove drill spoil from pile bases. A suitably qualified and experienced structural
or geotechnical RPEQ should inspect the footing excavations to confirm appropriate foundation
materials and cleanliness prior to pouring concrete.
If any ground conditions encountered during construction are found to differ from those noted above,
Tectonic must be notified immediately, and an inspection carried out to determine if changes to footing
design are required.


6.4           Retaining Structures
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 retaining structures could be carried out using a pressure distribution applicable to the wall
type and based on the parameters listed in Table 4. These values do not include allowance for
hydrostatic pressures nor transient (e.g. construction) or adjacent footing loadings.




Geotechnical Investigation & Slope Stability Assessment
9 April 2025 | 25050-001-Rev0                                                                               22