W6107fd f15.pdf - form 15 footing & slab design · OPW16/0220

Definitions.

Site classification – a broad measure of the potential ground movement of a site when
this site is subjected to loading by a structure (generally residential) and for a given and
controlled range of soil moisture changes – where the suction depth Hs is equal or
greater than 3 metres the classification is modified by adding a – D after the
classification letter ie M-D – class M with deep soil moisture suction changes.

AS2870 - 2011 has defined 7 site classes as follows:

Class                         Foundation movement from               Ys - site movement
                              Moisture changes

A - stable                    sand & rock sites.                     NA

S - slightly reactive         slightly reactive clays                0 to 20 mm

M – moderately reactive       moderately reactive clays              21 to 40mm

H1 – highly reactive          highly reactive clays                  41 to 60mm

H2 – highly reactive          very highly reactive clays             61 to 75mm

E – extremely reactive        extremely reactive clays               75+mm

P – problem                   varies                                 0 to 75+mm

Note: Problem (P) sites are normally classified because of limited bearing strengths at
normal footing depths - say 200mm below the ground surface where it is expected the
footings are to be supported by piers founded into strong material or where applicable
smaller differential movements can be catered for in the design by supporting the
structure with a heavy stiffened raft. Where a stiffened raft cannot cope with large
differential movements (or becomes less economic) then piles or piers are designed to
support the structure

Controlled fill – fill that has been placed & compacted in layers by compaction
equipment to a density defined by AS 3798 (Guidelines on earthworks for commercial
& residential developments) and able to achieve 100 kPa safe bearing capacity.

Rolled fill – fill compacted by rolling with an excavator. Sand material – compacted in
200mm layers up to 600mm thick. Clay based material – compacted in 150mm layers up
to 300mm thick. Where stated in this report “as rolled fill” the compaction is the same
but fill thickness may be increased and the footing and slab is supported on piers where
any fill exceeds 250mm in thickness.

Uncontrolled fill – fill that is neither rolled fill or controlled fill and which may cause
excessive settlement under footing & slab loads.




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