Attachment 4 - Geotech Report · MCU23/0030

                              50 NOOSA PARADE, NOOSA HEADS
                              PROPOSED RESIDENCE

determine the Design Geotechnical Strength (Rd,g). The Geotechnical Strength Reduction Factor should be
determined in accordance with AS2159 and is expected to be in the range of 0.45 to 0.55.
Settlements of piles founded as above under working or serviceability loadings would not be expected to
exceed 1% of pile diameter (e.g. less than 10 mm for pile diameters less than 1 m) provided pile bases and
sockets are cleaned of disturbed material and cuttings.
The exposure classifications for concrete and steel piles are likely to be ‘moderate to severe’ in accordance
with AS 2159 2009 Piling Design and Installation due to tidal influences.

6.3.4         Earthquake Design Considerations

Based on the information known from the current scope of investigation, and in accordance with Section 4.2
of Australian Standard AS 1170.4-2007 Structural design actions, Part 4: Earthquake actions in Australia,
this site would be classified as “Class Ce” (Shallow Soil Site).

6.3.5         Site Classification

We understand that site classification in accordance with AS2870 is considered as part of the hydraulic
design for a site when determining whether flexible plumbing connections at building junctions are required.
The potential relative movements between the anticipated raft slab supported building and surrounding
ground (i.e. at plumbing connection points) would not be expected to exceed 40 mm. Thus, an equivalent
Class M is recommended for hydraulic design purposes.

6.4       Permanent Drainage
Due to a number of factors, including potential for adverse environmental impacts associated with permanent
dewatering, the proposed basement should be designed as a fully ‘tanked’ structure. Design of the
proposed basement walls and floor will therefore need to include allowance for full hydrostatic pressures.
Although groundwater levels were measured at between about 1.8 m and 2 m BGL around the time of
investigation, groundwater could rise close to the ground surface following periods of heavy or prolonged
rainfall, and flooding.
The use of a passive pressure relief system could be considered to enable a reduction in the allowance for
hydrostatic uplift in the basement construction. This could comprise a drainage network connected to a
series of standpipes or one-way valves that allow groundwater seepage to flow into a sump-pump collection
system. A drawback of such a system would be the need for water quality treatment prior to off-site
discharge, and the on-going maintenance required. Design of basement tanking, and any pressure relief
system, must be undertaken by a suitably qualified and experienced structural RPEQ.
Permanent site drainage should be installed to ensure that stormwater runoff is directed away from building
walls and footings (e.g. perimeter paths/drains and swales where space allows).

6.5       Additional Investigation
With the scope of works requested for the investigation, and the current preliminary nature of the building
design, there are some outstanding geotechnical issues to be resolved for the proposed construction. In
addition, there are benefits (and potential cost savings) for the future design, along with mandatory
regulations which could be met utilising further geotechnical investigation. We would recommend that
following demolition of the existing residential structure, additional borehole drilling is undertaken at the site.
This should comprise drilling one borehole on the northern side of the site within the footprint of the proposed
pool using a 4WD mounted auger rig to 8 m BGL.
This borehole would provide the following information:
         Further information regarding the consistency and makeup of the deeper subsurface profile,
          allowing for identification of deeper compressible estuarine clay or loose sands within the alluvial
          sequence (if present at depth).


2 February 2023
Report No. 22500-001-Rev0                               12