How Foundation Soils Affect Your Foundation

What type of soil is around your foundation? Is it clay? Sandy? 

Depending on where you live, the ground will have its own unique composition. We put together an outline on how to identify the type of soil around your home, and how it impacts your foundation.

How water affects soil and your foundation

Different soil types are affected by moisture in different ways.

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Sandy Soils

Water does not have a big effect on sandy soil. When it rains, water passes through quickly and easily. Instead of expanding, sandy soils maintain a consistent volume and density, whether wet or dry.

Because of its stability and good load-bearing qualities, sandy soils are less likely to shift and settle. So it rarely causes foundation problems.

Clay Soils

Soils rich in clay and silt have greatest potential to cause foundation damage. Clay absorbs water easily, and expands in volume as it becomes more saturated. Expansive clays are what cause foundations to crack, heave, and shift. 

When the clay soil dries out, it shrinks and cracks. That shrinkage creates voids and gaps in the soil. When it rains again, that water can easily penetrate the clay and thus, repeat the expansion cycle. Clay-rich soils cause more foundation damage by expanding than by contracting.

Sandy Loam Soils

Sandy loam soils are usually stable and show little change with moisture level. The primary concern with loamy soils, though, is erosion. When the soil underneath your foundation erodes, it's unable to sustain the weight of your home.

Because of the constant wet-dry periods that occur as the weather changes, certain soil types can expand and contract indefinitely, subjecting your foundation to settling and expansive stresses that often cause damage.

The "active" zone of foundation soils

Illustration of the active zone around and underneath a foundation.

Your home is resting on many different layers of soil. And each layer has different thicknesses and characteristics that affect your home's foundation. 

Typically, soil layers gain stability and load-bearing capacity with depth. Deep below these layers is a layer of bedrock composed of rock or stable, densely packed soils. 

The soil that's directly beneath your home is known as the active zone. This soil is most affected by moisture and climate changes. And it's the source of most foundation problems. 

The active zone can vary from a few feet below the surface to more than 30 feet below grade.

How does foundation settlement occur?

Foundation settlement happens when the soil can no longer support the weight of your home. 

Three of the most common reasons for settlement are:

  1. Soil that's too dry
  2. Soil that's too wet
  3. Poorly compacted fill soil
Soil that's too dry

Soil experiences most of its drying and shrinking from two common causes:

  1. Drought: Prolonged dry periods cause soil to dry out. And when clay dries out, it shrinks. Soil shrinkage beneath a foundation causes a section of the foundation to crack and settle into the void. 
  2. Maturing trees: A tree's root system can be 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 significantly
Wetting and Softening of Soil

The soil around your foundation experience wetting and softening for two reasons:

  1. Heavy rain and flood: As clay soil gets wet, it expands and becomes very soft. This soft soil is weak and unable to hold load-bearing weight, causing the home to shift. 
  2. Poor drainage: If water pools next to your home, the soil will absorb that water and swell. As it does that, it'll start applying pressure to your foundation walls, causing them to bow and crack.
Poorly compacted fill soil

Before your house was a house, it was a plot of land. To prepare that plot of land for construction, builders brought in loose soil from another location to fill any hollow areas. This is called fill soil, and it's often looser and less compact than the dense, hard-packed virgin soils the site originally had. 

The fill soil has to be compacted thoroughly before a foundation is built, and if it's not, it will begin to compress underneath the weight of your home, creating foundation settlement problems.

stair step brick wall crack

Contact a foundation repair expert

If you have a foundation problem, we strongly suggest calling in a reputable foundation repair contractor. And if you're in our service area, we'd love to help.

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As a foundation repair company in business for over 45 years, Thrasher understands how Midwest soils affect your home. 

Our team of experienced specialists is ready to meet with you to explain what's happening to your foundation - and how to fix it.

To help you decide what's best for your home, Thrasher provides each of our customers with a free in-home inspection and no-obligation same-day quote. Each estimate includes a detailed proposal on how we plan to fix your foundation problem and protect your home. Call us today at 1-844-948-3306 or fill out this short form to schedule an inspection.

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