Geotehnical Investigation Report · OPW22/0140

                              PROPOSED UNIT DEVELOPMENT
                              37 BOTTLEBRUSH AVENUE, NOOSA HEADS

All footings should found such that they are not adversely affected by any adjacent excavations, trenches,
retaining walls, or in ground structures that are not designed to support building loads. Footings should
found at least below a plane extending 1 m horizontally from the base of trenches/excavations/retaining
walls/swimming pool, then rising up at 1V:1H, as illustrated in Text Figure 10.




                        Text Figure 10: Footing depth required to prevent undermining

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.

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.

6.4       Temporary and Permanent Retention
Excavations for the basement level may extend to depths of around 4 m BGL (existing ground levels) and, it
is likely that the basement footprint will extend close to some of the site boundaries, so some form of
temporary shoring may be required to support the basement excavation.

Based upon our experience with similar sites, we anticipate that temporary shoring may be achieved by use
of sheet piles. Such shoring techniques would likely require lateral restraint, and this is conventionally
achieved by anchoring. However, the proximity to neighbouring properties would require a number of
permissions to be obtained for subterranean access. Therefore, it is suggested that internal struts/propping
be considered to provide lateral restraint for the shoring system.

Anchored or propped sheet pile would likely require pre-drilling to prevent adverse vibrations during sheet
pile installation. Temporary lateral support can be provided by installation of helical steel anchors (similar to
screw piles) or internal props/struts connected to walers. As a permanent basement wall is constructed
inside the temporary structure, the sheet pile wall becomes sacrificial.

Other shoring methods that could be considered include contiguous or non-contiguous piles and secant
piles. The advice of a specialist shoring contractor must be sought regarding feasibility, design and
installation of the proposed retention and subsurface drainage 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.




13 May 2022
Report No. 22151-001-Rev0                               13