Geotech Report - techtonic · RAL22/0021

                              PROPOSED RESIDENTIAL DEVELOPMENT
                              39 PICTURE POINT CRESCENT, NOOSA HEADS

6.0      GEOTECHNICAL RECOMMENDATIONS
General recommendations to help maintain the stability of the site are given in the document Some
Guidelines for Hillside Construction, which is attached.

6.1       Development Limitations & Stability Discussion
It is anticipated earthworks will include cuts for the lower level of up to about 3 m to 4 m deep, in order to site
the lower level of the proposed residential structures. The extent of earthworks cuts 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).

Filling of up to 3 m to 4 m height is shown on the preliminary architectural concept drawings, however such
filling would result in an unacceptable surcharge over the sensitive dune slope, and resulting batter angle of
around 45° to be contained within the subject site. Localised levelling and grading may be permissible
elsewhere on the site, however fill heights should be limited to no more than 0.5 m above the existing ground
surface.

As mentioned above, the sand dune at this site is close to the ‘limit of equilibrium,’ where the FOS of the slope
is approximately 1.0. The dune slope at the site was 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 residential structures on the slopes 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 m in to the underlying dense sands and below a line at 28° drawn to extend upwards
from the toe (taken to be from Noosa Drive approximately), a Low Risk of slope instability would apply.

This is indicated conceptually in Text Figure 9 below.




                                                         Piles to found below plane at 28° and with 7 m embedment in to dense sand




                                                                                        Line at 28° from toe




Text Figure 9: Illustrative depths for piled footings




10 February 2023
Report No. 22511-001-Rev0                                11