What is slab heave and how does it affect houses?
Hi. I’m structural engineer Matt Cornell and this is my explainer video on slab heave.
G’day. I’m Matt Cornell from Cornell Engineers.
Today I’m answering a question about slab heave.
Before a house is built on a site, soil moisture conditions are fairly uniform across the site.
That changes when a house is built.
The uniform soil moisture conditions are interrupted by the house.
Slab heave occurs in clay soils when the soil moisture conditions under the house are no longer uniform.
When the soil around the outside of the house becomes wet the clay soils absorb moisture and expand.
The expansive forces are large enough to lift a house.
Under the house stays relatively dry.
There is a transition zone between the wet and dry soils as soil moisture transfers sideways.
When the soil around the outside of the house becomes dry the clay soils release moisture and shrink.
The ground surface moves down and the soil under the house is relatively wetter compared to the dry soils around the outside of the house.
Again there’s the transition zone between dry soils and wetter soils as moisture traverses from under the house towards the dry zone.
Soil moisture conditions aren’t only affected by changing seasons.
Other sources of soil moisture changes are garden irrigation, broken pipes, poor drainage and tree roots.
This has been Matt Cornell from Cornell Engineers talking about slab heave.
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Just a reminder:
- Not everyone who thinks they have slab heave does.
- Not everyone who thinks they have other problems does.
- Only use experienced structural engineers and geotechnicians to diagnose and fix house movement.
Contact Cornell Engineers for more information about slab heave and how to fix it.