Water is the main enemy in expansive soils problems. There is either too much water, causing the soil to swell, or not enough causing the soil to shrink. If all soils beneath a foundation swells uniformly or shrinks uniformly it is unlikely to cause a problem. But when only part of the foundation heaves or settles, differential movement causes cracks and other damage. Most differential movement is caused by differences in soils moisture. After construction, soil beneath part of the foundation becomes wetter or dryer than the rest of the soils. Click here to view the example.