 Foundation Failure! Every property owner fears it. But few truly understand the problem. Foundation failure is excessive upward or downward movement of the foundation, sufficient enough to cause structural cracks or deterioration of the building. It can be caused by one or several conditions, but movement of the soil is the most frequent reason. Of all the various soil types, clays that shrink and swell are easily the most problematic.
Soil expansion
In areas where expansive clay soils exist, when the moisture content within the soil increases, volumetric swelling occurs. As the soil swells due to the moisture increase, an expansion pressure is created that is far greater than necessary to actually raise a foundation.
 This upward foundation movement is termed "heave." Causes of soil swelling include moisture absorption due to poor drainage conditions around a foundation, plumbing leaks beneath foundations, or moisture available from springs or other underground moisture sources.
Soil Shrinkage
Shrinkage of the clay soil mass can occur when conditions that promote soil drying are present. As the drying action occurs, the soil loses moisture, which in turn allows the soil to shrink. When foundations are supported by the soil mass, shrinkage will allow the foundation to move downward, or settle. Shrinkage conditions are most commonly produced by periods of drought, excessive heat, high winds, and large trees or heavy foliage that pulls moisture from the soil.
Soil Consolidation/Erosion:
On cut and fill lots, soil consolidation commonly occurs when sites are developed by excavating soil from one area of the site and moving it to another area to level the construction pad. Often, so much fill is required, soil is imported from another site. The moved/imported soil is often
inadequately compacted to the necessary density to sustain the loads imposed. Therefore, it is common to find load related settlement when structures are built on large quantities of fill material. Also, if the fill material is a more granular material, erosion of the fill soils readily takes place. This erosion can be caused from leaks beneath the foundation system, or poor drainage conditions around the property. As well, if moisture moves through these soils, the soil particles can be carried away with the moisture flow, which in turn allows the soils supporting the foundation to collapse, thus producing foundation settlement. Vibratory soil consolidation from traffic or machinery vibrations, is another common causes of settlement. The above merely represents the most common causes of foundation failure and by no means is intended to cover all the reasons a foundation may have failed.
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