Appendix B - Geotech and Acid Sulfate report - MCU19-0030

Gympie Terrace Noosaville Pty Ltd




Executive Summary
This report presents the results of a geotechnical and Acid Sulfate Soils (ASS) investigation carried out for a
proposed unit development at 217 to 219 Gympie Terrace, Noosaville. The proposed development is to
comprise a three-storey apartment building with a single level basement carpark.
The general subsurface profile comprised loose to dense silty sand topsoil, overlying; alluvial soils
comprising loose to medium dense, grading to dense to very dense sands; underlain by medium to high
plasticity, firm to stiff, clay and silty/sandy clay materials. Residual soils were encountered beneath the
alluvial soils at depths of between 7.5 m and 8.5 m (RL -5.7 m and RL -6.8 m AHD), and comprised stiff to
very stiff, medium plasticity, silty sandy clay.
Groundwater inflow was encountered in all boreholes between 1.2 m and 1.5 m BGL (RL 0.17 m and RL
0.55 m AHD). Groundwater in the standpipe in borehole BH1 was measured at 2 m BGL (RL -0.23 m AHD).
Excavation for the basement to approximately 2 m BGL (~RL -0.3 m AHD) should encounter mainly loose to
medium dense (or denser) sands. Such excavation should be achievable using conventional earthmoving
equipment (e.g. 12 to 20 tonne tracked excavators).
Anticipated building wall and column loads (up to 2500 kN) could be supported by 3 m square pad footings.
The subgrade at the basement excavation must be compacted/densified with a smooth drum vibrating roller
with water applied if necessary, to achieve the required allowable bearing pressure (i.e. approximately
300 kPa) for the nominated pad footings. Total settlements of up to 30 mm and differential settlements of up
to 15 mm are anticipated below the nominated pad footings.
A suitably designed stiffened raft slab could also be used. Anticipated total settlements for a raft should be
less than 50 mm with differential settlements less than 25 mm. Alternatively, if these settlements cannot be
tolerated, the building could be supported on screw/driven piles.
Temporary shoring of the basement excavation using engineer-designed anchored (or internally propped)
sheet-pile walls will be required during basement construction. Sheet pile walls can also be used as
permanent basement walls thus reducing ‘lost’ space.
Provided that the sheet piles are founded in the stiff clay, sump pumps in the excavation base should be a
suitable dewatering method.
Consideration must be given to the effect of groundwater drawdown on neighbouring properties and in-
ground services during construction dewatering. Re-injection of the groundwater outside of the excavation
could reduce the impacts of groundwater drawdown effects.
The results of aggressivity laboratory analysis indicates an exposure classification of ‘Mild’ to ‘Non-
Aggressive’ in accordance with Table 6.4.2(C) and Table 6.4.3(C) of AS 2159-2009.
The results from the investigation indicate that low levels of existing acidity and potential ASS (PASS) are
distributed throughout the natural sands across the site. Calculation of liming rates required for full
neutralisation of combined existing and potential acidity are presented below:

        Natural Sands (0 m to 1 m BGL)            5 kg CaCO3/m³
        Natural Sands (Below 1 m BGL)             15 kg CaCO3/m³
Given the anticipated volume of soils that will be disturbed and required lime treatment, management of
existing and potential acidity at this site would be classified as VH (very high). The SPP14 guidelines require
that for Category VH treatment, a stand-alone ASS Management Plan (ASSMP) must be provided.




J000799-002-R-Rev0                                                                                   Page i