RFI - 21327-001-Rev0 Plover St

                              PROPOSED RESIDENCE
                              34 PLOVER STREET, PEREGIAN BEACH

6.3.2       Footing Design
No design loadings were available at the time of reporting. Footings for the proposed development and any
ancillary structures (e.g. retaining walls, pool etc.) must penetrate through any fill materials and unsuitable
natural soils (i.e. very loose to loose sands) to found at least 0.5 m into medium dense (or denser) natural
sands. Such materials were encountered at about 2 m BGL (existing ground levels) in the boreholes. Thus,
piled footings will be required unless excavations expose such materials at or near foundation subgrade level.

Piles so founded may be designed using an allowable end bearing pressure of 300 kPa. High level footings,
where achievable in deeper cut areas, may be designed using an allowable bearing pressure of 100 kPa
provided that they are founded in the natural medium dense (or denser) sands. Settlement under such loads
is expected to be in the order of up to 20 mm or 1% of footing width.

Given the sandy soil profile and depths of footings required, steel screw piles are considered to be a suitable
foundation type for the proposed development generally. However, in areas of cut exposing medium dense
(or denser) sands at the subgrade level high-level footings may be adopted. It should be noted that
excavations for concrete strip footings (or similar) may loosen the base. Therefore, the use of a vibrating
plate would be required to densify any high-level footing bases prior to the placement of reinforcing steel.

Due to the presence of loose sands and nearby structures, open bored piers or driven piles are not
considered to be suitable for this site and it is expected that steel screw piles could be utilised. Steel
reinforced concrete bore piles may be possible; however, the use of sacrificial liners (e.g. Formatube) would
be required. The advice of a specialist piling contractor must be sought regarding feasibility, design and
installation of the piling system for this site, including an assessment of potential vibration effects on nearby
structures, and monitoring requirements.

If steel screw piles are adopted, it will be important to ensure close supervision of installation, as piling may
not encounter sufficient drilling resistance (from torque measurement) in sands at the suggested founding
depth, and piles could extend to much greater depth than necessary.
It is therefore recommended that site specific static load testing be conducted from screw piles, if adopted, at
a minimum. Where tension or compression capacity developed in the footings is critical for the future
structure (e.g. resistance to uplift forces from high winds), then cyclic load tests (including measurement of
deflections under tension and compression cycles) should also be undertaken prior to construction.
Kentledge for static testing, or simulated cyclic loads, should prove the piles to a minimum of two times the
expected working load within tolerable deflections.

Footing design should also account for potential soil reactivity to be equivalent to Class M. It should be noted
that placement of reactive clay may result in a more severe equivalent site classification, such as H1 or
greater.

All footings should found such that they are not adversely affected by any adjacent excavations, trenches,
retaining walls, or in ground structures that are not designed to support building loads. Footings should
found at least below a plane extending 1 m horizontally from the base of trenches/excavations/retaining
walls/swimming pool, then rising up at 1V:1H, as illustrated in Text Figure 9 overleaf.




10 September 2021
Report No. 21327-001-Rev0                               11