The attached article provides a nice overview of the cause and results of expansive soils (http://www.usinspect.com/resources-for-you/house-facts/environmental-concerns-home/expansive-soils).  The example of the change in the soil from adding a little bit of water is very instructive.  It is easy to see how a home or building constructed on expansive or clayey soil can experience significant damage from the addition of a little water.  A common scenario is the addition of water from landscape irrigation, which can result in soil movement.  A small amount of soil movement can result in substantial damage to the building structures, and surrounding improvements, such as flatwork, roads, etc. 

     Keep an eye on any cracking occuring at your building.  If the crack is progressing over time, by getting longer or wider, this may be an indication of subsurface soils movement.  A particularly telling sign of a problem is a crack that is offset:  I. E. one side of the crack is higher than the other side.  An offset crack should be a particular cause for concern.