2 Types of Soils in Arizona and How They Affect Development

Whether you’ve just bought a plot of land or you’re ready to begin the due diligence process before breaking ground on a site, conducting a geotechnical survey or soil analysis is a critical first step. Commercial development projects of any size, in any location, are complex and involve several successive tasks that compound in scope. For example, before you start construction, you need a level site. Before you level a site, you need to pull all relevant permits and approvals.

A geotechnical survey, or soil study, is typically the first step in that long list of tasks. Soil studies help you understand the composition of a lot’s soil, laying the figurative foundation for any development project. In Arizona, there are several different types of soils that developers should be aware of. The type of soil on your lot has a big impact on the overall viability of your development.

What kind of soil does Arizona have?

Aside from tropical soils, you’ll find just about every common type of soil in Arizona. Most soils in the state have a high clay content, making them very alkaline. These desert soils can be low in nutrients and very hard to work with, so many development projects require the addition of composted organic matter to help the soil hold water and nutrients. Arizona soils are so difficult to work with that most of them are considered “problem soils” because they expand and collapse so easily.

When you perform a soil profile test on a given site in Arizona, you’ll find that most soil profiles have two distinct layers called horizons. Horizons can vary widely in color, consistency, structure, and texture, as well as chemical composition and characteristics. Typically, the surface and subsurface of a site consist of the coarsest soil layers, while the subsoil is finer and firmer and has a lower organic matter content.

Why is organic content so important for soils? It helps soils hold nutrients and water to support plants. The organic matter content is often higher in soils that haven’t been cultivated for a long period of time. Arizona’s soil content only contains about 1% organic matter. It’s very slow to accumulate in the arid conditions characteristic of Arizona weather. 

Instead, Arizona soil consists mostly of clay, which is often problematic for developers because clay soils contract and expand. When wet, clay soils can expand greatly in volume and have the potential to collapse drastically. This puts the foundations of buildings at risk. When dry, the soil shrinks, causing a wide variety of problems like cracked foundations, ruptured pipelines, and warped roads. 

Types of Arizona soils

There are two primary types of soils in Arizona, each with its own unique characteristics.

  • Casa Grande soil: Casa Grande soil is the most common type of soil in Arizona and has a high clay and salt content. This soil can only support certain types of plants. Its high salt level leads to shrinking, imposing some limitations on residential and commercial construction, like over-excavating and backfilling with coarse, textured material. The construction process also brings more slat to the surface, and the salt-affected topsoil is more susceptible to blowing. Additionally, salt brings a high possibility of the corrosion of materials like steel pipes or concrete.
  • Caliche soil: Caliche is common throughout Arizona in subsoil, the layer below the surface soil. This layer can be up to 6 feet deep, and the soil particles are cemented together with calcium carbonate. Building on a lot with caliche soil is extremely difficult since hand-digging in this area is nearly impossible. Crews often need a jackhammer to do any major digging. Roots can’t penetrate caliche, and water can’t move through it. While it’s strong and stable, caliche is hard to get through, presenting challenges for developers and construction teams.

How does soil fit into your development strategy?

Geotechnical surveys are critical to determining whether the Arizona soil on your land can support foundations and buildings. They also help determine what lies below the surface, including any considerations that might impact a project’s budget and timeline. No matter the size or scope of your development project, understanding the soil composition of your site is a critical part of predevelopment and development. It requires substantial investigation to determine whether your project is feasible or not.

By identifying potential soil issues before breaking ground, you can avoid wasting time and capital. You need a partner who understands the complete due diligence process so that you can maximize value and execute your project without delay. Sandbox Development provides a full scope of due diligence services, such as feasibility reports including soils and environmental, archeological, and biological factors. Reach out today to learn more.