Sunshine Butterflies - Attachment D - 010816-2

                              OUR BACKYARD
                              468 MCKINNON DRIVE, COOROIBAH

6.2       Building Foundations
6.2.1        Indicative Site Classification
Site classification for footing design is determined in accordance with AS2870-2011 Residential Slabs and
Footings, and depend on the depth of cut / fill undertaken at a site, variations in the natural soil / rock depths
and reactivity of the in situ soil and any imported fill materials.

Based on the results of the investigation, the site classification for the existing natural soil profile in the
proposed building areas is Class H1. Characteristic ground surface movements (‘ys’) at this site are expected
to be around 40 mm. It should be noted that the predicted order of movement is based on the existing soil
profile (i.e. no cutting or filling), and moisture content changes within soils due to normal seasonal moisture
variations only.
Due to the highly reactive nature of the clay soils, it would be prudent to implement the following practices to
minimise changes in soil moisture:
       Prevent drying of the clay soils during construction by minimizing exposure of cut batters and
        excavation subgrades. This may be achieved by measures such as covering batters with HDPE
        (‘black builders plastic’), staging earthworks to minimize soil exposure before covering with
        structures, leaving subgrades ‘proud’ prior to final trimming, and placement of ‘blinding’ layers across
        the excavation subgrade and footing bases (e.g. crushed rock).
       Install and maintain temporary drainage to prevent saturation of the site during construction.
       Seal the ground surface around the building perimeter (e.g. concrete or paved pathways).
       Plant/maintain shrubs/trees at least a distance from the building equal to the mature height of the
        shrub/tree.
       Maintain stormwater drains to prevent overflow into soils and repair any damaged drains
        immediately.

The use of flexible service connections would be necessary for this site. Potential ground surface
movements are in the high range and have the potential to affect the operation of services if flexible
connections are not installed.

6.2.2        Footing Design
Footings should be founded at least 0.1 m into stiff (or stiffer) natural clays, or loose to medium dense (or
denser) natural sands, and designed using an allowable bearing capacity of 100 kPa.
All footings should found such that they are not adversely affected by any adjacent excavations, batter slopes,
trenches, or retaining walls that are not designed to support building loads. To minimise the potential for any
adverse interaction effects, footings should found at least below a plane extending 1 m horizontally from the
base of trenches/batter slopes/excavations/retaining walls, then rising up at 1V:1H. This requirement is
illustrated in Text Figure 7 below.




Text Figure 7: Minimum footing depths to minimize risk of undermining




4 May 2016
Report No. 16081-001-Rev0                                7