Soils and Foundations - How Soil Supports and Damages Your Foundation

At any location, the soil profile is comprised of multiple soil types and layers. Soil types vary in moisture, density, and strength with depth. Soil eventually transitions to bedrock. This layering process occurs naturally over time by glaciers, water, and wind.

Fill soil is a term most often used to describe the soil that is excavated from one location and moved to a new location for the purpose of land development, particularly in residential housing developments. In much residential land development, areas of land are cut back, and then filled. It is not uncommon to find fill soil over areas with native, undisturbed soil.

Soils either become weaker or stronger with depth. Depending upon the natural weathering process of the soil or bedrock, or the environment in which the soils were deposited. Generally, soils become stronger with depth, and eventually extend down to bedrock. If homes are built on weaker surface soils, shifting and settling of the structure are naturally occurring processes over time.

In most circumstances, foundation solutions that extend through the weaker surface layers to more competent, dense layers below, will provide an enduring solution to settlement issues.

How Foundation Soils Affect Your Home’s Foundation

Sandy soil and sandy loam soils expand and contract very little with moisture changes. They can be very reliable when supporting a foundation.

Clay soils expand and shrink in volume dramatically with moisture changes and can cause significant foundation damage.

What Is Your Home Sitting On?

The simple answer is the ground. However, the real answer is a bit more complicated than that.

Soils are composed of different ingredients like sand, silt, loam, and clay. These ingredients determine how soils behave under wet and dry conditions and when they need to support weight. Soil characteristics have a major effect on a house foundation.

Soil Types

The Active Zone Of Foundation Soils

Moisture And Soil

Different soil types are affected by moisture in different ways. Each of these three soils reacts to water differently:

  • Sandy Soils
  • Clay Soils
  • Sandy Loam Soils
Active Zone

Illustration of the active zone around and underneath a foundation.

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

Your home is resting on many different layers of soil, each with different thicknesses and performance characteristics that can affect a house foundation.

These soils have been formed or deposited there over thousands of years—some by water, some by wind, some by glaciers, and some by the contractor who built your home.

Typically, soil layers gain in stability and load-bearing capacity with depth. The surface layer is made up of organic materials, making it easy for plants and vegetation to grow.

As you go down, you'll find layers of sand, silt, clay, and loam soils, depending on where you live. Deep below these layers is a layer of bedrock. Bedrock is a layer composed of either rock or very stable, densely packed soils.

The soil you should be most concerned about is known as the active zone immediately around and underneath the house. This soil is most affected by changes in moisture and climate—and the source of most foundation problems. The active zone may vary from a few feet below the surface to more than 30' below grade, depending on what area of the country you live in.

Our team of in-house foundation contractors can get your home back on solid ground! Call us at 563-202-1650 for a free foundation repair quote today! We serve Davenport, Peoria, Waterloo, Iowa City, and many nearby areas in Illinois and Iowa.

How Does Foundation Settlement Occur?

Foundation settlement is the movement your foundation experiences when the soil can no longer support the weight of your home. Three of the most common reasons for foundation settlement are drying and shrinking of soil, wetting and softening of soil, and poorly compacted fill soil.

Dry Soil

Drying & 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. As we know, when clay dries out, it shrinks. 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.

Wet Soil

Wetting & Softening Of Soil

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

Heavy Rain & Flood Conditions: As clay soil gets wet, it holds on to water and becomes very soft. This soft soil can be weak, causing the home to shift (or sink) down into it.

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

Poorly Compacted

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 haven't been disturbed.

The fill soil brought in 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.

Our Foundation Repair Contractors Proudly Serve IL and IA

As a locally owned and operated foundation repair company, we understand the ways that soils in Illinois and Iowa affect the homes they surround. Our team of in-house foundation contractors is ready to meet with you to explain what's happening with your foundation—and how to fix it.

To help you decide, we provide each of our customers with a free, no-obligation foundation repair quote, in writing, before you spend a dime with us. Each quote includes an on-site inspection, a personal consultation, and a detailed proposal on how we can work to fix your problem.

We proudly serve Davenport, Peoria, Waterloo, Iowa City, nearby areas such as Normal, Iowa City, Dubuque, Rock Island, Clinton, Moline, East Peoria, and the surrounding areas of IL and IA.