Geotechnical Report

 J000206-001-R-Rev0                                                                                     April 2016

Further details for control and testing of fill are given in Australian Standard AS 3798-2007 Guidelines on
Earthworks for Commercial and Residential Developments.
In accordance with good construction practice, fill embankments should be ‘over built’ then trimmed back to
the well compacted material.
Controlled fill placed as described above could be formed at 1V:2H provide adequate erosion protection is
installed.
            Footing Design
6.2.1           Site Classification
The site classification derived in accordance with Australian Standard AS2870-2011 Residential slabs and
footings can provide an indication of the likely magnitude of reactive (shrink and swell) movements
associated with normal seasonal moisture variations. Based on the results of the investigation, the site
classification is expected to be ‘Class ‘H2’ in accordance with AS2870-2011. The estimated ‘ys’ value for this
site is between 60 mm and 80 mm.
It should be noted that the predicted order of movement is based on the existing natural soil profile (i.e. no
cutting or filling), and moisture content changes within soils due to normal seasonal moisture variations only.
This estimate assumes that earthworks will be limited to stripping and minor levelling of the building platform.
Earthworks comprising filling or cut excavations greater than 0.5 m could result in a different site
classification.
As the site soils are ‘reactive’, it will be necessary to ensure that ‘usual good practice’ is adopted for design
and detailing if control of reactive ground movement is desired. Such practices should include the following:

       Trees and shrubs should not be planted or be allowed to remain closer than their mature height to
        movement sensitive features.

       Soil moisture should not be allowed to change during or following construction.

       Site grades should be designed to readily shed water and prevent ponding around footings and other
        movement sensitive areas.

       The proposed buildings should be made as “flexible” as possible to cope with reactive soil movements.

       Services beneath the buildings should be kept to a minimum and should be designed to be flexible
        (especially at building walls), and to prevent any leakage.

6.2.2           High Level Footings
Building wall and column loads could be supported by strip or pad footing system suitable for a Class H2 site
classification. Footings should penetrate through any uncontrolled fill or unsuitable natural soils to found at
least 500 mm below platform level (750 mm below ground for articulated full masonry) and 200 mm into the
natural stiff (or stiffer) clay.
The following allowable bearing pressures may be adopted in natural materials for design purposes:
    -      Stiff clays:                                      100 kPa

    -      Very stiff clays:                                 200 kPa;

    -      Hard clays and extremely low strength siltstone: 400 kPa.

Footings founded within engineered fill placed in accordance with the recommendations provided in Section
6.1.4, could be designed with an allowable bearing pressure of 100 kPa.
To achieve the design recommended pressures, footing excavations must be dry and cleaned of any loose,
disturbed or saturated materials prior to pouring concrete. Footing excavations should be inspected by an
engineer from Core to confirm the foundation material meets the design pressure requirements.
If any soil conditions encountered during the footing excavations are found to differ from those noted in the
geotechnical investigation, Core should be notified immediately, and an inspection of the footing excavations
should be carried out to assess if changes to footing design are required.




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