How Soil Affects St. Louis Area Building Foundations
Eastern Missouri’s soil is mostly clay which is similar to a sponge, it shrinks when dry and swells when wet. Many homes are on multiple types of soil so that different parts of your home may be shifting at different rates.
- Clay—Kaolinite, Illite, Smectite/Montmorillonite - Water molecules attach to inner and outer layers of soil particles and push particles that expand the volume of the soil. As water molecules evaporate, clays consolidate and shrink.
- Organics—Black decaying or decayed vegetation
- Very low density and bearing capacity
- Suspends in water for a long time
- Silts—are very fine soil particles and are some of the least reliable for load bearing. Capacity with moisture. Silts can only be compacted by dynamic compaction, they will rebound at a later date and cause structures to uplift. Normally, consolidated silts will compress under a load when wet.
Water can move horizontally and vertically through the soils under your foundation in a similar manner. As clayey 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 the soils vary from location to location. For example, Jefferson City may have more rock based soils while Warrenton would hold more clay soils.
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.
While the soils vary from town to town, it is important to maintain your structure if you live in St. Charles, St. Louis, South County, North County or anywhere else in Missouri. If you are getting ready to build, prevent foundation settlement issues before you build with new construction piers. Contact us today for details.
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