Unstable One of the most common causes of foundation movement under homes is the shrinkage
and swelling of reactive clay soils. The degree of movement is determined by the amount of
expansive material and the variation of its moisture content. During the drier months when
the moisture content decreases the soil shrinks, allowing foundations to settle.
During the wet season when the moisture content of the reactive clay soil increases, the soil
swells and foundations return to their original levels. Sometimes, the soil will swell
enough to
raise foundations higher than their desired level, which is referred to as heave. Foundation
movement may be caused by a variety of other factors, these include:
Stable Poor site drainage: Moisture should be diverted away from the building in order to maintain
uniform moisture content to preserve the strength and levels of the foundation. Adequate site
drainage is very important to prolong the life of the structure.
Un-compacted fill material: This fill material will consolidate or pack down under the load
of its
self weight and the weight of the structure over time. Moisture problems will contribute
to the
consolidation of un-compacted fill material.
Leaking plumbing and/or over watering of gardens: Differential soil movement will also occur
when underground plumbing services leak or when a garden is watered on one or two sides
of the building and the remainder is paved over. This has the potential to cause heave on one
side and shrinkage on the other side. This situation has often resulted in excessive stress being applied to the concrete slab, resulting in internal partition walls lifting from the
slab and cracking the gyprock walls and ceilings.
All sites will be affected by differential soil moisture content to some degree with “H” “E” or “P”
sites being particularly susceptible to foundation movement.
A recent High Court decision (Bryan V Maloney) has firmly established that home owners
are no longer prepared to accept slabs that are designed on the basis that a varying degree
of foundation movement will occur during the life of the structure nor will they accept the
requirement that home owners need to maintain the foundation site conditions.
How and why IdealSlab™ works
IdealSlab™ is a fully developed and certified slab system that has now been in service
for many years, supporting thousands of homes.
IdealSlab™ is designed to provide a fail-safe solution to the problems encountered with
differential movement of the slab/structure caused by near surface soils that are affected by
either soil swell, shrinkage or by fill settlement.
IdealSlab™ is a fully suspended slab that is built on the ground without the requirements for
footings excavation. The slab and the structure are fully supported on a grid of IdealPier™
driven deep into firm ground.
On “H” and “E” sites the soil is scarified to a specified depth, typically, from 600 to 800 mm.
The scarification process is used to induce voids to the sub-soil strata. In the event of the soil
swelling the heave forces are dissipated into the scarified cavities. This process neutralises
potential damaging uplift forces acting to raise the slab and the structure off the ground. On
“E” sites, this can be up to 100mm. of heave or settlement.
On sites affected by soil shrinkage or fill settlement the grid of IdealPier™ provide the required
uniform support to the slab that will prevent the structure from settling differentially.
IdealSlab™ has been designed to support the house or structure without failure, irrespective of
underlying reactive clay soil movement or fill settlement.