geotech report · MCU15/0087

Slope Stability and Geotechnical Assessment
1 Natasha Avenue, Noosa Heads




4.       Surface Conditions
The site is located at the junction of Natasha Avenue and Banksia Avenue in Noosa Heads. It is
bound by Natasha Ave in the south, Banksia Ave in the west, the Noosa River to the north and an
adjacent vacant allotment to the east.

The site has two distinct topographical zones. The southern part of the site adjacent to Natasha
Avenue is at the top of the dune at an elevation of about 27 metres and is relatively flat with a gradient
to the southwest between 5 and 8 degrees. This area has been recently cleared and is largely devoid
of grass and trees with only a fringe of grasses and small trees along the Natasha Avenue frontage.

The northern part of the site is on the escarpment and falls steeply to the Noosa River in the north.
The gradient as measured in the field varies between 35 and 38 degrees. Narrow terraces formed
from timber sleepers supported by steel star pickets have been constructed to provide access down
the escarpment to the river. The escarpment is vegetated by medium to small trees and a ground
cover of shrubs, grasses, weeds and forest debris is present.



5.       Subsurface Conditions
5.1. Geology
The site is located on a Pleistocene aged dune. According to the 1:100 000 Geological Series
mapping, sheet 9444 and part 9545, prepared by the Department of Mines and Energy Queensland,
the dune formation is mapped as Pleistocene Dune (mapping unit Qpd 2) and is made up of quartz
sands. This is consistent with Coffey site observations.

5.2. Subsurface Profile
The subsurface profile has been inferred from the geological mapping of the site, Coffey’s site
observations and borehole and DCP testing undertaken on the site by Coffey. The profile consists of
deep quartz sands to depths in excess of 6 metres.

On the flatter area at the top of the dune, the sands are loose to depths up top 0.5 metres grading to
medium dense, dense and very dense with depth. Dense sands were present at depths greater than
2 metres. Very dense sands were indicated at depths in excess of 4 metres.

On the escarpment of the dune, loose sands were present to depths between 1.5 and 2.0 metres.
The sands graded rapidly to very dense with depth. Very dense sands were present at depths
greater than 2.5 metres.

5.3. Groundwater
Groundwater was not encountered during investigations on the site. Due to the permeability of the
sands and the high gradients, it is unlikely that high standing groundwater levels will occur on the site.
However, saturation of the upper profile of the sands may occur in high intensity rainfall events or due
to anthropogenic incidents.




Coffey
GEOTKPAR02068AA/A                                                                                        2
12 August 2015