geotech report · MCU15/0087

Slope Stability and Geotechnical Assessment
1 Natasha Avenue, Noosa Heads




6.       Design Considerations
6.1. Shrink Swell Movements
The site is underlain by clean quartz sands. These materials are non-reactive and shrink swell
movements on the site will be negligible.

6.2. Allowable Bearing Capacity
The allowable bearing capacity at the crest of the escarpment in the loose sands to depths up to 0.5
metres has been assessed to be less than 40 kPa. Founding of structures in these upper loose
sands is not recommended.

At depths greater than 0.5 metres, medium dense to dense sands are present. An allowable bearing
capacity of 100 kPa may be adopted for design in these deeper sands. Higher allowable bearing
capacities are available at depth over most of the site. Coffey should be consulted should higher
bearing capacities be required.

6.3. Settlements
Compressible strata were not encountered on the site. Some minor settlements less than 10 mm can
be anticipated under likely structural loads on the site.

6.4. Site Classification
Sites for domestic dwelling may be classified for footing design purposes in accordance with
Australian standard AS2780-2011. This site has been classified as Class P in accordance with
AS2780-2011. This classification is due to low allowable bearing capacity in the upper sand profile
and the potential instability of the dune escarpment on the northern side of the proposed housing
envelope.

6.5. Founding Conditions and Footing Systems
As the footing requirements will be dictated on this site by slope stability considerations,
recommended footing systems and founding conditions are provided in Section 7.8 following
discussion of the stability risks.

6.6. Cut and Fill Earthworks
Soils on the site are clean sands. These soils are suitable for reuse as structural fill providing that
they are handled and managed in according with Australian Standard AS3798-2007. A minimum
compaction requirement of 70% Density Index is recommended for any structural fill.

6.7. Retaining Walls
The following design parameters set out in Table 1 may be adopted for retaining wall design on the
site. Retaining structures would be designed by a professional engineer in accordance with the
requirements of AS4678-2002: Earth-Retaining Structures and adequately designed for earth
pressures, surcharges and elevated ground water conditions. The adopted design should also
include drainage and maintenance measures.



Coffey
GEOTKPAR02068AA/A                                                                                         3
12 August 2015