One study showed that 60 percent of all residential foundations built on expansive soils experience some distress, and 10 percent experience problems sufficient to require repairs. Before attempting repairs you must think through what caused the damage, how best to repair it, and, perhaps most importantly, how to prevent the problem from recurring.
CAUSES OF DISTRESS
Water is the basic culprit in all expansive soil problems. There's either too much water, causing the soil to swell, or not enough, causing the soil to shrink. Most differential movement is caused by differences in soil moisture. After construction, soil beneath part of the foundation becomes wetter or drier than the rest of the soil. There are several possible reasons for this: abnormal soil moisture during construction, loss of soil moisture, or gain of soil moisture.
Repair contractors can only raise structural members. They can't reasonably lower them. The two most common methods of repair are mechanical jacking and slabjacking. Mechanical jacks can exert very high local pressures. In a slabjacking operation, grout is pumped beneath a slab or beam to produce a lifting force that restores the member to its original elevation. The grout is a mixture of water, cement, and soil, sand, or fly ash. Lime also may be added to the grout.