Foundation settlement and movement in Missouri is typically caused by building on expansive clay, improperly compacted fill soils, or improper maintenance around foundations.
Foundation failure may occur due to a variety of causes. Sometimes root expansion can shift a foundation off its footings. Soil composition, moisture levels, and settlement are contributing factors. Fill soil that is washed away or that swells due to plumbing leaks or other sources of excess moisture can cause shifting, instability, and cracking in your foundation. Drought, freezing and extreme temperature changes are also concerns.
Observing soil moisture changes around your foundation is possible, but what about under it? Moisture can move from outside to under your foundation through a property of soils known as suction. Soil suction is similar to placing just a corner of a dry, compressed sponge in contact with a puddle of water. In a short time, the sponge has drawn water throughout itself and grown in volume.
While a water source is present, the sponge will continue to absorb water until it is saturated. If the water source is cut off, then water already in the sponge will distribute itself evenly, but the sponge will not reach saturation.
Water can move horizontally and vertically through the soils under your foundation in a similar manner. As clay-like soils draw water to themselves, they too grow in volume (swell or heave) causing your foundation to move. Drying outside your foundation reverses the process. The moist soils will lose volume (shrink) as soil moisture moves out from under your foundation, causing the foundation to settle. Shrinking and swelling soil motions can lead to damaging your foundation and structure. Uniform changes in soil moisture are less damaging to your structure than localized changes. We know that soils vary from location to location. For example, Jefferson City may have more rock-based soils while Warrenton would hold more clay-based soils.
Other Causes of Foundation Failure
- Cut and fill land development
- Water run-off
- Moisture trapped by flowerbeds
- Water ponding
- Low-density soils
- Under-compacted fill
- Negative drainage or plumbing leaks
- Construction when soil was dry with subsequent heaving
- Rebound—cut hillside relieves overburden pressure and exposes dry, dense soil
- Settlement—drying clays shrink at different rates causing foundation failure
- Subsurface hydrostatic liquefaction—when fill soil is dumped over an old, wet-weather stream or hillside seep. The lower layers become saturated, liquefy, and flow from under the upper layers
- Total collapse of surface soils—caused by saturation, deforestation, and removal of support soils at the toe of the hillside