Geotechnical Investigation Report · OPW26/0149

                                                                                                 PTG/04982 – 0001 – Rev0 – Rev0



We point out that the analyses have been undertaken assuming the earthworks for the development are carried out
in adherence, or in excess of the recommendations provided in Section 9 below. In this respect, construction
observations and confirmation of site preparatory work and fill placement is recommended. Where the works are not
undertaken in accordance with the provided development recommendations, the short-term and long-term FoS for
the stability of the proposed dam is likely to differ from the values presented in Table 7, to the point where
unfavourable FoS values that could lead to failure of the dam are possible.
We also point out that the analyses check for global stability only. Other dam related stability concerns, such as piping
erosion, have not been assessed as this is beyond the programming of the Slide2 software.



9 GEOTECHNICAL RECOMMENDATIONS
The geotechnical recommendations presented herein are based on the factual information collected during the
fieldwork, the results of the laboratory testing, the results of the slope stability analyses undertaken, geotechnical
engineering best practice, local experience and published literature. Irrespective, the recommendations provided are
still, fundamentally, an opinion.
In summary, the ground conditions that are likely to be encountered at the site can be characterised as comprising a
residual soil consisting of stiff to hard silty CLAY. Pre-existing fill materials are not anticipated in any notable quantity,
and none were encountered in our investigation.
Based on the ground conditions, it is likely that the most suitable foundation system for the buildings would comprise
shallow piers supported in the near surface residual soils, designed in general accordance with AS2870:2011.

     9.1 SITE CLASSIFICATION
Based on the subsurface conditions encountered during the investigation, the site is considered to comprise naturally
occurring fine-grained soils with a low to moderate shrink–swell potential. The site is assessed to be subject to normal
site moisture conditions in accordance with AS2870.
The site investigation did not identify the presence of uncontrolled fill, existing structures, significant vegetation
influences, or other abnormal site conditions that would warrant a Class ‘P’ classification under Clause 2.1.3 of
AS2870.
The characteristic ground surface movement (Ys) value in the location of the proposed cabins has been determined
from the results of shrink–swell index (Iss) value returned from BH01, which suggests a characteristic ground surface
movement a in the order of 20 mm to 40 mm as per AS2870:2011. This level of ground movement is consistent with
a Site Class ‘M’ (moderately reactive clay site) in accordance with AS2870:2011.
It should be noted that the site classification does not include any tree effects, or any existing or future filling works,
which may result in increased ground movements.
This classification is applicable to sites subject to normal moisture conditions. Changes to site conditions, such as the
introduction or removal of trees, poor drainage, or development of gardens adjacent to footings, may result in
increased ground movements and potential structural damage.

     9.2          Earthworks Advice
    9.2.1       Excavation Conditions
Excavation of the residual soils could be achieved using excavators of any size. As a rule of thumb, refusal for a ute
mounted drill rig with 100 mm augers is generally the depth where a 30-tonne excavator fitted with a 600 mm wide
bucket and tiger teeth will encounter bucket refusal.


    9.2.2       Suitability of Site Won Material
With the exception of any topsoil or materials containing notable organic inclusions, most of the materials won from
the site excavations are expected to be suitable for reuse as structural for the dam. Provided that there are no
limitations on fill (i.e., shrink-swell, CBR, WPI), site materials could be considered suitable for reuse as structural fill
for the dam.




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