Chemical Soil Injection

Chemical soil injection is a proven method used to reduce the swell potential of expansive clay soils beneath residential and commercial foundations. The process is very similar to standard water injection but includes the addition of specialized chemical solutions that help stabilize the soil and limit its ability to expand and contract with moisture changes.

This method is commonly recommended by geotechnical engineers in areas where expansive soils are known to cause foundation movement.

How Chemical Injection Works

The chemical injection process follows the same general procedure as water injection. Injection rods are inserted into the ground to deliver a solution deep into the soil profile. The key difference is that the injected water contains chemical additives that alter the behavior of expansive clay soils, helping to reduce their ability to swell.

Hole spacing is typically the same as with water injections, but total water usage is often lower because the chemical additives increase the effectiveness of the treatment. In many cases, only one or two passes are needed for chemical injections to achieve the desired soil stabilization.

If the soil is extremely dry, a preliminary water-only pass may be performed before the chemical treatment begins to help the solution penetrate the soil more effectively.

Site Preparation

Site preparation for chemical injection is similar to the process used for water injection. The foundation pad should typically be no more than 12 inches below the finished subgrade when using on-site soils. This allows room for the soil to expand slightly during the treatment process.

Concrete forms should not be set until the chemical injection process is complete and the site has passed the required post-injection swell testing performed by a certified engineer.

Injection Process

Once the foundation pad is properly prepared, the treatment area is chemically injected to depths generally ranging from 8 to 12 feet, depending on the recommendations provided by the project engineer.

Engineers commonly require treatment of the soil within five feet of the foundation perimeter as well. This perimeter stabilization helps reduce soil movement near the edges of the structure.

Injection rods are typically spaced five feet apart, with each additional pass offset between previous injection points to create an effective spacing of approximately 2.5 feet across the treatment area. Injection holes are never reused.

Each injection rod is driven into the soil at 12-inch intervals, allowing the chemical solution to penetrate the soil evenly. The injection rod typically remains at each interval for 30–45 seconds, or longer when soils are extremely dry or compacted.

To improve penetration and distribution, wetting agents called surfactants are often added to the injection solution. These agents help the water and chemicals spread more efficiently through the soil. The injection solution often appears dark brown due to the natural color of the surfactant used in the process.

Chemical Solutions Used

Atlas Soil Stabilization commonly uses acid-based soil stabilization solutions, which are highly effective at reducing soil swell potential. However, we can inject a variety of chemical treatments depending on the recommendations of the project engineer or the specific needs of the site.

One alternative option is potassium chloride injection, which can also be very effective at stabilizing expansive clay soils. While potassium chloride treatments tend to be more expensive, they are sometimes recommended for specific soil conditions.

Whenever possible, it is best to follow the treatment method recommended by your geotechnical engineer to ensure the soil stabilization process meets project specifications.

The Role of Drainage

While chemical injection is highly effective at stabilizing expansive soils, it is important to understand that no soil stabilization method can control or divert underground water flow. Groundwater movement can still cause deeper soils to swell regardless of treatment.

For this reason, proper grading and drainage around the foundation are essential to maintaining long-term structural stability.

The ground surrounding the structure should:

• Slope away from the foundation

• Include proper drainage systems

• Use hardscape surfaces such as concrete or pavers with drainage when appropriate

The International Residential Code (IRC) provides clear guidelines for grading and drainage around foundations. Following these guidelines helps reduce the risk of soil movement caused by water accumulation.

When soil stabilization and proper drainage are combined, they provide a highly effective solution for protecting residential and commercial foundations from damage caused by expansive soils.

Please see the Moisture maintenance Recommendations.