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When they are dry, swell ing soils often can be recognized by their Ilpopcorn!1 appearance. 38 Characteristics Swell ing soi Is contain a high percentage of certain kinds of clay particles which are capable of absorbing large quantities of water. Soi I volume may expand 10 percent or more as the clay becomes wet. The powerful force of expansion Is capable of exerting pressures of 20,000 psf or greater on foundations, slabs or other confining structures. Subsurface Colorado swell ing soi Is tend to remain at a constant moisture content In their natural state and are usually relatively dry at the outset of disturbance for construction on them. Exposure to natural or man-caused water sources during or after development results in swell ing. In many instances the soi Is do not regain their original dryness after construction, but remain somewhat moist and expanded due to the changed environment. Consequences Swe I I i n9 so II s are one of the nat i on t s most preva lent causes of damage to bui Idings and construction. Annual IOsS6S are est I mated in the range of $2 b i I I Ion. The losses i nc I ude severe structural damage, cracked driveways, sidewalks and basement floors, heaving of roads and highway structures, condemnation of bui Idin~s, and disruption of pipel ines and sewer lines. The destructive forces may be upward, horizontal, or both. Aggravating Circumstances Design and construction of structures whi Ie unaware of the existence and behavior of swell ing soi Is can worsen a readi Iy manageab I e s i tuat i on. Where swe II i ng so II s are not recognized, improper bui lding or structure design, faulty construction, inappropriate landscaping and long term maintenance practices unsuited to the specific soi I conditions can become a continuing, costly problem. Design problems might include improper foundation loading, improper depth or diameter of dri lIed piers, insufficient reinforcing