Attachment 2- soil stability report · MCU14/0017

                                                                                    Report No. 13N 682




        3.3       Groundwater

Groundwater is not expected to be of concern at the site due to the relatively free draining nature
of the in-situ sandy soils.

        3.4       Footing Design

It is recommended that the proposed residence and all associated structures including the pool
and garage be founded in dense silty sand or better, expected at depths greater than 3.6m below
natural ground level.

In accordance with good hillside building practice, and to provide lateral resistance to potential
downslope soil movement, it is recommended that steel reinforced concrete bored piles be
adopted for the foundation of the residence at this site.

Based on the results of the site investigation undertaken by Geotechnical Testing Services it is
recommended that the following estimated parameters be adopted for design of the proposed
footings:

Table 2 - Estimated Design Parameters for Bored Piles
                                                          Ultimate Unit Stresses (kPa)

    Founding Material Description                   End Bearing                Shaft Adhesion

              Silty Sand - Dense                        300                              -


In order to adequately assess the pile capacity, a geotechnical strength reduction factor (Φg)
should be applied to the ultimate unit stresses estimated above in accordance with AS2159-2009 –
“Piling – Design and Installation). The geotechnical strength reduction factor (Φg) will depend on
various assessed factors associated with this site including the geological complexity of the site,
extent, amount and quality of geotechnical data, design experience in site geology and method of
assessment for assigned geotechnical parameters.

Based on general assumptions about the use of bored piles at the site, it is assessed that a
geotechnical strength reduction (Φg) factor of between 0.40 and 0.47 be adopted for preliminary
pile design purposes at the site. It is however the responsibility of the designer to make an
appropriate assessment of the geotechnical strength reduction factor (Φg) based on their risk
circumstances.

This assessment is based on the assumed absence of any pile load testing of constructed piles at
the site. Should pile load testing be undertaken a higher geotechnical strength reduction factor
may be adopted in accordance with AS2159-2009 – “Piling – Design and Installation.

Shaft adhesion should not be considered in the material encountered at this site.

As a general rule, a length to diameter ratio (L/D) of 4 or greater is recommended for the socket
length into the recommended founding material (dense silty sand).




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