Attachment 4 - Geotech Report · MCU23/0030

                              50 NOOSA PARADE, NOOSA HEADS
                              PROPOSED RESIDENCE

level should be negligible. Settlements of less than 40 mm are anticipated. An allowable bearing (contact)
pressure of 100 kPa may be adopted for raft foundation design.
The effects of hydrostatic uplift / buoyancy need to be considered and tie down anchoring or piles may be
required.
Excavations for the basement are expected to expose mostly loose to medium dense sand across the
subgrade level. Over-excavation and replacement of any unsuitable materials with select granular fill may
be required (e.g. about a 200 mm layer working platform). The ability for the temporary shoring system to
support over-excavation should be considered in the design of the walls if a raft footing option is adopted
and a contingency for additional propping, anchoring or material lime treatment may need to be allowed for
to enable deeper excavations. Select fill materials, placement and compaction would need to comply with
Section 6.1.5. The raft subgrade must be inspected by a geotechnical RPEQ to confirm the foundation
materials and allowable bearing pressure, and to advise on treatment of any unsuitable zones.

6.3.3         Piled Footing Design

To achieve a non-worsening of global instability for the existing rock revetment along the river, the proposed
pool and outdoor entertaining area, should be supported on footings (piles where necessary) founded into
medium dense (or denser) sand at least 2 m BGL. Consideration should be given to differential movements
due to these structures being outside the proposed basement as discussed in Section 6.3.1 above.
Where piles are required, it may be possible to obtain sufficient pile load capacity founding in the medium
dense sands present from about 2 m BGL (existing ground surface). Based on the subsurface conditions,
suitable pile types that could be considered include:
        CFA grout injected piles
        Steel screw piles (lightly loaded piles only)
Bored piles would not generally be suitable due to the presence of sandy soils and groundwater, and would
need to be constructed using liners, in conjunction with dewatering and tremie equipment. Reinforced
concrete driven piles would not be suitable due to potential installation vibration effects on the surrounding
structures. The advice of a specialist piling contractor must be sought regarding an assessment of suitable
pile types, pile design, and associated constructability considerations. The most cost effective piling solution
depends on a combination of pile type, diameter and length. Piling companies are best equipped to make
this assessment based on the costs of the various options.
Piles may be designed using the ultimate end bearing and ultimate skin friction values present in Table 4
below.

Table 4: Ultimate Pile Design Parameters

            Material Type                 Ultimate End Bearing (kPa)           Ultimate Skin Friction (kPa)

                  Fill                                   NR                                 NA

   Medium Dense Sand present
                                                         675                                 20
        below 2 m BGL

    Very Dense Indurated Sand
                                                         2500                               100
      present below 7 m BGL

Notes:
1) NA – Not Applicable; NR – Not Recommended

Ultimate geotechnical capacities (Rd,ug) determined from the parameters provided in Table 4 must be
multiplied by a Geotechnical Strength Reduction Factor (øg) in accordance with Section 4 of AS2159-2009 to



2 February 2023
Report No. 22500-001-Rev0                                 11