Foundation Soils

The only thing more important to the stability of your home than its foundation is the ground upon which it’s built. This soil must be stable in order to support the weight of your home and its contents for decades to come. Unfortunately, it is all too common for foundation soils to become unstable over time for a variety of reasons.

sand loam clay foundation ground soil

Sandy soil (left) and sandy loam soils (middle) expand and contract very little with moisture changes. They can be very reliable when supporting a foundation. Clay soils (right) expand and shrink in volume dramatically with moisture changes and can cause significant foundation damage.

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active soil in northern georgia

Illustration of the active zone around and underneath a foundation.

For instance, red clay can absorb lots of water and expand during wet weather and can shrink during times of drought. This expansion and shrinkage can cause serious foundation issues. The fill soil that results when a developer levels a neighborhood in preparation for building can sometimes be poorly compacted. This too can result in foundation settling and other issues.

In fact, entire neighborhoods have had their foundations repaired because they were built on poor soil. That means, even if you haven’t had foundation problems yet, you may still experience them sometime in the future. So, if you think your home may be built on poor foundation soils — or if you have neighbors who have had issues — it may be time to have an expert visit your home and determine if it needs to be protected against future foundation failure.

Further information on foundation soils can be found on the following pages:

shrinking soils foundation

Drying and Shrinking Of Soil

Foundation soils experience most of their drying and shrinking from two common causes:

Drought: Prolonged dry periods cause soil to dry out. Soil shrinkage beneath a foundation has the same effect as soil settling: It usually causes a section of the foundation to crack and settle into the void or hollow area where settlement has occurred.

Maturing Trees:The root system of a tree can be up to twice the size of the tree’s canopy. If a tree’s branches extend over your home, there’s a good chance that they extend under your house as well, drawing moisture up from the soil and causing it to shrink.

footprint sinking in mud

Wetting and Softening Of Soil

The soils around your foundation experience wetting and softening primarily for these two reasons:

Poor Drainage: If water is allowed to stand, pool or “pond” next to your home, the soil will absorb the water. As it does, the soil can weaken and soften yet again.

Plumbing Leaks & Broken Water Lines: When a home’s plumbing begins to leak under a slab foundation, the soils underneath can begin to become saturated, weakening their supporting capacity.

soil excavation

Poorly Compacted Fill Soil

In order to level a site where a foundation will be built, builders sometimes bring in loose soil from another location to fill depressed or hollow areas.

This newly moved “fill” soil is much looser and lighter than the dense, hard-packed virgin soils at the site that has never been disturbed.
The fill soil poured by the builder has to be compacted thoroughly before a foundation is built on top of it. If the soil is not compacted well, it may begin to compress underneath the weight of your new home, creating settlement problems that can damage your foundation.

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