Damage to homes and commercial structures in the US is commonly related to soil characteristics, with expansive (shrink/swell) soils and collapsing soils causing the most problems. Cracking of foundations, walls, driveways, swimming pools, and roads costs us millions of dollars each year in repairs. Severe or recurring damage can lower the value of a house or property. According to the American Society of Civil Engineers, about half of the houses built in the United States each year are situated on unstable soil, and about half of these will eventually suffer some soil related damage. This damage causes greater financial loss to property than earthquakes, flooding, hurricanes and tornados combined.
Each spring and summer homeowners in Texas are reminded of this, as the moisture content of their expansive clay soils dramatically increases and decreases with the seasons. The causes of soil expansion or collapse are related to the type of clay minerals in the soil and original soil density. A change in soil moisture content can cause clay minerals to swell like a sponge or to collapse as it dries. Expansive clay soils can cause walls and foundations to crack and roads and sidewalks to warp.
The first sign of expansive soils causing a need for foundation repairs is when you notice a misalignment of doors and windows. Another indication of soil expansion is when your patio or driveway slabs buckle or move away from the house. Non-load-bearing walls, which do not have enough weight to resist the pressure produced by expansion, typically crack before load-bearing walls do. Upon drying, expansive soil shrinks, forming large, deep cracks or "popcorn" texture in surface exposures.
Decreasing the effects of expansive clay soils can be accomplished several ways. The application of hydrated lime to swelling soils is a common treatment that is usually effective in reducing expansion. Another effective method is to replace the expansive soils with non-expansive fill. This can only be accomplished in new construction projects. The application of protective barriers, such as geo-membranes, that surround the homes foundation help keep soil moisture levels constant and prevent the infiltration of surface water.
For larger problems caused by expansive soils, helical piers or steel piers can be an effective solution. These piers extend the foundation below the active soil layers to a non expansive stratum of soil. The key to these types of foundation repair techniques is depth. One must bear these piers on deep soils at least three times their diameter below the expansive layers.
Poor drainage can result in ponding of water, which allows clays to absorb water, expand and cause problems. Gutters and downspouts should direct water at least 10’ away from the foundation to help maintain consistent soil moisture. Deep watering of landscaping plants and lawns by drip irrigation systems also can trigger soil expansion.