Attachment 4 - Site Investigation and Slab Report

                                                                                Joint width INCREASES at top of wall




    More flexible wall types such as clad frame
walls with timber or metal studs will also benefit
from articulation to reduce the risk of surface
distress and window and door jamming due to
                                                                                Joint width as constructed
foundation movement.
    The construction of a building on a reactive         DOMING CAUSED BY SWELLING OF REACTIVE SOILS
soil site typically causes changes in the moisture
content of the soil under the building relative to the                          Joint width DECREASES at top of wall
surrounding soil. After the construction of slab-
on-ground footings the soil beneath the slab will
generally have a higher moisture content than the
surrounding soil, causing reactive soils to swell
and form a mound. Strip footings with suspended
flooring systems, which provide ventilation under
the floor, generally cause the soil beneath the
floor to dry causing reactive soils to shrink and
form a dish. Seasonal weather changes (ie dry and                               Joint width as constructed
wet periods) will cause reactive soils around the        DISHING CAUSED BY SHRINKAGE OF REACTIVE SOILS
exposed edges of the building to also either swell
or shrink. This may increase the mounding (dry           Figure 1 Effect of ground movement on footings and
periods) or even cause dishing of slab-on-ground         articulated walls
footings if the moisture increase around the edges
is more than that under the slab (wet periods)
Figure 1.
    The differences in the soil movement cause
the greatest problems. Doming and dishing of the
foundation soil and footings – although it may be          Articulation joint
only a few millimetres – causes distortion in the          may commence
walls. Articulation is designed to accommodate             above DPC if
                                                           close to footing
such movement by dividing walls into smaller
panels that can move independently of each other,          Damp-proof
thereby minimising the risk of cracking in the walls.      course (DPC)
    Doming and dishing of the footings means that
articulated wall panels need to be able to move
in their own plane, with the articulation joints
opening and closing in response to the foundation
movement. The articulation joint width and details
(eg sliding or vertical expansion joint ties) should
allow for this movement. Note that the foundation
movement associated with reactive soils generally
occurs over long periods (say 12 to 18 months) due       Figure 2 Articulation joint above damp-proof course
to the relative impermeability of the clay materials
that typically cause the swelling and shrinkage
movements. Thus joints will tend to open or close
seasonally with prolonged wet or dry conditions,
rather than over short periods.
    It should also be noted that the greatest opening
or closing occurs at the top of an articulation joint,
with little or no movement at the bottom (ie at the
top of the footing). For this reason, provided that
some hairline cracks in the wall just above the
footing is acceptable (usually concealed within the
mortar joints), articulation joints may start above
the level of the damp-proof course Figure 2. This
has the advantage of providing less interference to
the installation of damp-proof courses and termite


                                                                                                   Articulated Walling Page 3