Does chemical soil stabilization work on Oklahoma clay?

Reviewed by Preston, Oklahoma foundation repair consultant · Updated 2026-10-14

In short: Chemical soil stabilization adds lime or another chemical to expansive clay to reduce how much it swells and shrinks. Oklahoma highway research shows lime can nearly eliminate swell in some Oklahoma soils and make it dramatically worse in sulfate-rich soils. Testing the soil, especially for sulfates, comes before any treatment decision.

What is chemical soil stabilization?

Expansive clay swells when wet and shrinks when dry. Most foundation repair works around it, by placing piers below the moving layer or by controlling water. Chemical stabilization tries to change the clay itself.

Engineering guidance for swelling soils lists two ways to deal with the soil directly: remove it to an adequate depth and replace it with compacted non-expansive fill, or treat it chemically on site, noting that adequate amounts of lime or cement can reduce swell potential in most expansive soils ³. A Texas regulatory bulletin on residential foundations lists stabilizing the soil by chemical dewatering or chemical presaturation (pre-wetting the clay) among alternatives for compressible or shifting soils ⁵. Colorado State University Extension describes lime treatment at 2 to 10% mixed 12 to 18 in deep, along with vertical or horizontal moisture barriers installed by builders ⁴.

What approaches are used?

What did Oklahoma research find?

The University of Oklahoma, working for the Oklahoma Department of Transportation, tested lime, fly ash and cement kiln dust on Oklahoma soils after curing ¹:

Swell in the lime- and kiln-dust-treated samples was traced to ettringite, confirmed by microscope and X-ray analysis; the kiln dust itself carried about 28,133 ppm sulfate ¹.

These were laboratory mixes for highway pavement design, compacted in molds ¹. Pressure injection into undisturbed clay under an existing house is a different process, and the lab numbers do not transfer to it directly.

What is the sulfate problem?

Ettringite is a calcium-aluminum-sulfate mineral that forms when lime, soluble sulfate (often from gypsum), aluminum from clay and water combine; it can swell up to 250% of its original volume ². In 2004, several miles of State Highway 412 near Woodward failed from sulfate-induced heave after a gypsum-rich subbase was treated with lime, and repairs cost the state millions ². Published sulfate limits for lime treatment range from about 700 to 8,000 ppm, and the Oklahoma researchers questioned whether a 3,000 ppm threshold developed in Texas applies to Oklahoma soils ². The SH-412 subbase came from a borrow source with large amounts of gypsum ²; gypsum-bearing rock in Oklahoma is described under Permian gypsum units.

Which Oklahoma soils are candidates?

Oklahoma State University testing found montmorillonite-dominated clay in western Oklahoma benchmark soils, with Kirkland showing volume change up to 73% and Bethany up to 66% ⁶. The researchers treated shrink-swell values above a set threshold as a sign of substantial smectite and severe limits for engineering use ⁶; see clay mineralogy.

What testing is needed before treatment?

• Plasticity index and swell tests on samples from the depth to be treated; see soil testing and lab values.
• Soluble sulfate content, because of the ettringite reaction ².
• Swell tests on treated and untreated samples, the comparison the Oklahoma studies used ¹.
• Follow-up elevation and moisture monitoring after treatment.

Full study details are summarized in OK Data - Stabilization Research. Stabilization is often discussed alongside root barriers and moisture control and the active zone.

Related

• OK Data - Stabilization Research
• Clay Mineralogy
• Soil Testing and Lab Values
• Shrink-Swell and Active Zone
• Root Barriers and Moisture Control