SPECIAL PROBLEMS OF CLAY SOIL IN FOUNDATION OF BUILDING BASICS AND TUTORIALS

PROBLEMS OF CLAY WHEN PRESENT ON THE FOUNDATION OF BUILDING
What Are The Problems Of Clay As Foundation?


Special Problems of Clay Soils
The majority of clay soils can cause foundation problems as they slowly change in volume due to increases or decreases in water content. This change is related to the season with the ground expanding in the winter and
contracting in the summer.

This seasonal change, which may be in the order of + or - 30mm at ground level, can affect the clay to a depth of about a metre, with the ground below this level having a fairly stable moisture content.

Where clay soils contain trees the problem is more severe. Trees and heavy vegetation draw a considerable amount of water from the ground during the growing season.

A mature poplar takes up as much as 1000 litres of water per week. In long hot summers with little or no rainfall the tree will continue to draw moisture out of the ground and the clay will shrink.

This, of course, is in addition to the seasonal drying mentioned above. If buildings are sited near individual or groups of trees serious cracking in the walls can occur as a result of ground movement.

To prevent this movement from affecting strip foundations they must be deeper than the tree roots. An alternative, of course, is to site the buildings well clear of the trees.


Where trees have been removed from clay soils the opposite problem occurs. As the ground slowly regains moisture it will expand and this can continue for a period of up to 10 years.


The pressure that dry clay develops when reabsorbing moisture is likely to be greater than that imposed by the building load and upward movement of the structure will occur.

If houses are built on the site before this ground expansion is complete, cracking will occur in the walls and foundations; the swelling will be uneven because it will be concentrated around the removed tree.

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