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Ground Movement - Shrink / Swell of Clay

Main Factors

Foundations on clay, dry and wet weather and climate, trees

What is Shrink / Swell?

All clay soils change volume as their water content changes through the year, generally wet and swelling in winter, and drying and shrinking in summer.

Why is it a Problem?

Shrink / swell at surface is not usually a problem to buildings and services. However, it does become a problem if the ground beneath building foundations shrinks and swells, as the movement may vary across the foundations. This causes differential movement in the foundations and increases the likelihood of damage to the foundations and cracks in walls. Differential movements redistribute the structural loads, causing load concentrations on the foundations which may not have been taken into account during design.

Where Does it Happen?

Shrink / swell is most likely, in areas where shrink/swell susceptible clays occur, with drought and often where there are trees or where trees have been removed.

Causes of Ground Shrinkage

Shrink / swell clays when drought occurs. This will be made worse if trees are growing nearby.

Causes of Ground Swelling (Heave)

Prolonged rainfall after dry spell and removal of trees near the buildings or building on land the previously had trees and hedges, particularly if the foundations are directly above where trees and hedges were growing.

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