RFI - Attachment 6 - Technical Note

4 February 2021


Devcon Property Group
Attention: Mr Simon Drew

Email: [email protected]




PROPOSED INDUSTRIAL COMPLEX
11 LEO ALLEY ROAD, NOOSAVILLE

Dear Simon,
At the request of Devcon Capital 9 Pty Ltd (Devcon), Tectonic has reviewed supplied documents to enable
the provision of the geotechnical advice given below for a proposed retaining wall at the above site. The
following documents were reviewed:

       CSI Soil Testing (CSI) report 13971, dated 18/01/2021.
       Blackburne Jackson architectural drawings 31317-DA01 to DA-14, not inclusive, dated 13/01/2021.
       Covey Associates Pty Ltd (Covey) civil design drawings 192297-C001 to C-411, not inclusive,
        various issues and dates.

We understand that a cut is proposed along the western boundary of the site to depths of not more than
1.5 m below ground level (BGL). The Covey design specifies sheet pile walls to provide temporary support
to the cutting along most of the western boundary, with permanent support presumably to be provided by
concrete tilt panels which will form external walls to the adjoining industrial unit buildings. A short intervening
area between the units, at an existing sewer crossing, is to be retained using masonry block walls supported
on concrete bored piles taken below the sewer invert level (Covey ref. RW4). We are advised by Devcon
(email dated 3 February 2021) that the Covey design is to be amended to include concrete block masonry
walls along the western boundary of the units, in place of concrete tilt panels.

The CSI soil test indicates that three boreholes (denoted BH1 to BH3) were drilled along the western side of
the site, in proximity to the proposed sheet pile walls. These boreholes encountered similar subsurface
conditions comprising an upper layer of variable materials including soft to stiff clays, sands and gravels to
about 0.5 m BGL, then very stiff to hard natural silty clays to drilling termination at 3 m BGL. Soils in these
boreholes were mostly described as moist, however some very moist and wet soils were indicated by CSI in
the upper materials in boreholes BH2 and BH3.

Available aerial imagery, and anecdotal information provided by Devcon, indicates that there are no buildings
or sensitive structures within at least 2 m of the western boundary on the neighbouring property to the west.

Provided that the upper variable soils are benched no steeper than 1V:1H (e.g. 0.5 m horizontal bench), and
that significant groundwater seepage is not encountered during construction, the temporary, unsurcharged
cutting along the western boundary through very stiff to hard natural silty clays may be formed vertical to a
height of not more than 1.5 m. The cut must be retained within two weeks of excavation, unless a longer
timeframe is approved following inspection of the excavation by a suitably qualified and experienced RPEQ
geotechnical engineer (‘Geotechnical Engineer’).
We therefore suggest that the proposed concrete block walls for the western units could be used to provide
permanent support to the western boundary cutting, and that the proposed sheet piles would not be required
subject to implementation of the above advice during construction. Details for waterproofing, drainage and
backfilling behind the block retaining walls would need to be assessed and detailed by a structural engineer.


                                                    Tectonic Geotechnical Pty Ltd
                                                   PO Box 899, Buderim, QLD 4556
                                      Office: (07) 5478 9016 Email: [email protected]
                                                       www.tectonicgeo.com.au
                                                         A.B.N. 83 165 727 828