Expansive Soil

Page Summary

• Expansive Soil, especially expansive clay, changes volume with moisture and can create deep cracks during dry seasons and swelling during wet periods.
• Clay minerals like smectites and bentonite drive swelling behavior, with soil maps and soil testing helping identify risk before construction.
• Moisture swings and poor drainage can trigger foundation movement, with stabilization methods such as lime and fly ash blends and common foundation repair approaches used to address damage.

Expansive Soil is a moisture sensitive ground condition that can swell when wet and shrink when dry, creating movement that stresses slabs, foundations, and interior finishes. The behavior is closely tied to clay mineralogy, including expansive clays such as smectites and bentonite, which can absorb water and expand significantly. Understanding local soil conditions through regional maps and project specific soil testing helps property owners and builders reduce settlement and heave risk, especially where drainage and seasonal moisture changes can intensify soil movement.

What is Expansive Clay Soil?

Expansive clay soils have a high mineral content and are susceptible to large changes in volume. They can also develop deep cracks, especially during dry seasons. Soils containing expansive mineral content are called vertisols. This article discusses their properties and how they affect gardening. In addition to soil types, expanding clay soils can have several other unique characteristics.

Expanding clay soils

If you’re planning to build a house, you might want to consider the properties of expansive clay soils before you start your project. These soils are typically more expansive than other soil types, and their volume increases when wet and contracts when dry. You can easily identify expanding clay soils with the help of regional maps. Moreover, it’s important to undergo soil testing before constructing your house to ensure that the soil you’ll build on is safe for your foundation and your house. More about expansive soil.

Expanding clay soils are common in many areas of the United States. Located from Colorado to Florida, they form in residual environments. The USGS published a Swelling Clays Map of the Conterminous United States 1989. The soil’s potential to expand largely depends on the natural moisture content of the surrounding areas. Early assessment of your project’s soil condition is critical so that you can take appropriate measures to minimize the settlement risk.

Smectites

Smectites are highly reactive and have significant adsorption capacities. Their negative charge in the soil makes them extremely reactive. In addition to water, smectites adsorb herbicides, natural organic compounds, and ions. Therefore, it is important to carefully control the smectite minerals for proper identification and quantifying the amount of these compounds in soil. More about expansive soil.

This unique property of smectites in soil enables it to absorb and expand significant amounts of water. These smectites can cause soils to undergo a 30% change in volume with a change in temperature or moisture. Houston Black and Sugar Land soils are examples of smectite-rich soils. A study conducted on five map units in northern Virginia revealed that these inclusions affect the foundations and properties of the soil.

Bentonite

If you live in expansive soil, you probably have seen Bentonite in your cat litter or “speedy-dry” agents. This clay is an absorbent and swelling clay. Its main component is montmorillonite, which is either sodium or calcium. The sodium variety is the swelling clay, while the calcium form has the least swelling. When it becomes wet, it expands up to 16 times its volume and absorbs up to 10 times its weight. Bentonite is a common component of 4% of soil, leading to foundation issues, heaved floors, cracked drywall, and other problems.

The ability of expansive soil to exhibit swelling and downward settlement in buildings is often underestimated. A recent study conducted in Biswas, Rajdip, examined the effect of fly ash on the strength and swelling of a single-story residential building. National Institute of Technology researchers visited the site on November 19th, 2015.

Fly ash

A lime and Fly Ash mixture stabilizes expansive soil, reducing its plastic limit and unloading swelling ratio. The mixture’s maximum strength is at least 10% fly ash. Adding up to 5% lime to the mixture increases its hydration rate and early strength. In addition, it increases the soil’s unconfined compressive strength. These properties make Fly Ash an excellent choice for expansive soil stabilization. In addition, it reduces the risk of premature failure of treated expansive soil during wet-dry cycles.

In a study of the cementitious effect of fly ash on the expansive soil, researchers discovered that 5% lime and 20% fly ash combined with limestone improved the unconfined compressive strength of the stabilized expansive soil. The resulting mix also decreased the number of desiccation cracks. The resulting mix increased UCS by about 24%, compared to 14.5% with plain soil. Further, fly ash combined with limestone increases the strength of expansive soil.

Foundation repair options

Many types of foundation repair options exist for homes built on expansive soil. These repairs are often required to support more soil around the

Foundation Expert James Belvillefoundation, such as a crawl space or basement floor. A professional can assess the condition of your home’s foundation and offer a free estimate. A foundation repair professional can assess existing damage as well as potential structural problems. Here are three types of solutions for homes built on expansive soil.

Call Concrete Repairman James Belville at 502-418-2970.

Soil damage happens when the moisture content of the soil varies dramatically. If you have expansive soil, it will double in volume if the temperature and moisture levels are drastically different. Expansive soil will wreak havoc on your home’s foundation if placed in an area of poor drainage. If this happens, the foundation will shift upward, and any utilities connected to it will begin to fail. More about expansive soil.