Meyer Judgment Sealed

 

tecténic PROPOSED RESIDENTIAL DEVELOPMENT
bed Rie tte 39 PICTURE POINT CRESCENT, NOOSA HEADS

 

Executive Summary

This report details the results of a geotechnical investigation undertaken for a proposed residential
development at 39 Picture Point Crescent, Noosa Heads. The investigation was performed by Tectonic for
HM Property Pty Ltd. The investigation comprised drilling of boreholes at two locations across accessible
areas of the development footprint, together with in-situ soil strength testing. One stand-alone in situ strength
test (using the dynamic cone penetrometer method) was also undertaken. This report summarises the
results of the investigation and provides geotechnical recommendations regarding earthworks and footings,
together with temporary and permanent retention.

Based on the provided information we understand that it is proposed to reconfigure a single existing lot
(Lot 2 on RP220514) in to two separate lots being an equitable 723 m? in land area. Concept architectural
drawings provided to us with the project brief indicate that following subdivision, each new lot may be
developed with residences, reaching up to four storeys height. The extent of earthworks cuts or the nature
of the proposed structures has not been indicated on the drawings provided, and the findings of this
assessment should be reviewed once detailed architectural drawings are available (to confirm feasibility).

The subsurface conditions encountered in the boreholes, and inferred from deeper DCP testing at the
boreholes, are summarised as follows:

« — Fill — comprising very loose to loose sands (encountered in borehole BHT-2 only) to a depth of
0.7 m BGL; then, or from ground surface level in borehole BHT-1
» Natural Sands:
© being very loose to depths of between 1 m and 2 m BGL; then
o loose to between 2 m and 3.6 m BGL; underlain by
o medium dense sands to between 3.8 m and 4.6 m BGL; followed by
o dense sands to the testing termination depths of between 4.8 m and 5.6 m BGL.

No signs of groundwater seepage (‘springs’) were observed during our walk-over. Groundwater was not
encountered in the boreholes at the time of the investigation.

The sand dune slope to the rear of this site is close to the ‘limit of equilibrium’ (at an inclination of just over
30°), and thus relatively shallow, translational movements could be expected in such a situation. Deep seated,
global instability impacting the proposed residential structures at this site is unlikely to occur provided that
the footing system is adequately designed. It is assessed that where piles are taken to found a minimum of
7 min to the underlying dense sands and below a line at 28° drawn to extend upwards from the toe of the
slope (taken to be from Noosa Drive approximately), a Low Risk of slope instability (to property) would apply.
In an adverse case, where ongoing near surface instability occurs on the dune face below the proposed
buildings, and retrogresses; it is possible that the piles may become exposed above the ground surface
temporarily. Thus, some form of lateral capacity must be allowed for in the pile design to address this.

A grout ‘curtain’ must be installed along the northern edge of the buildings (at the slope crest) to a depth of
no less than 6 m. The plane extending at 28° from the toe has also been used to inform the need for
protection to the side boundaries. It is possible that sand would be removed from neighbouring properties
with ongoing instability on the dune slope, which has the potential to affect the subject site where the building
envelopes do not extend as far north/downslope. The grout curtain should also extend from the northern
edge of the building envelopes, and south along each respective site boundary for about 10 m, tapering from
6 m deep at the northern end.

All excess stormwater collected around the residence (including overflow from rainwater tanks etc.) must be
directed by pipes or lined channels to the nearest legal point of discharge. Where possible, utilising a ‘wet’
or ‘charged’ system where necessary, stormwater collected from the roof and other elevated hard surfaces
should be piped to discharge into the kerb along Picture Point Crescent. Where this can only be designed to
take some flows; stormwater will need to be directed to the dune slope to the north (ultimately leading to the
road reserve for Noosa Drive), where it is suggested that an RPEQ designed stormwater dissipation and
infiltration device should be installed. The device must be designed and constructed to ensure a non-
worsening impact from stormwater runoff on the neighbouring properties/infrastructure down slope.

 

10 February 2023
Report No. 22511-001-RevO ii

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