There are three basic soil conditions that pose particularity serious problems for architects, engineers and building contractors. First is the swelling and shrinkage movements of expansive clays; secondly, the occurrences of settlement or densification from load bearing forces; and, thirdly, the influence of moisture on the soil and building structure. Individually any one of these soil behaviors would create tremendous economic damage to a building structure.
The chemical stabilization process addresses these three basic soil concerns in several meaningful ways including: reduction of shrink/swell potential and plasticity on expansive clays, increased load bearing support as measured by unconfined compressive strength, and reduction of the treated soils permeability, making it less susceptible to water infiltration.
Expansive soils cover one-fourth of the United States. Expansive clay soils undergo large amounts of heaving and shrinking due to seasonal moisture changes. These movements lead to cracking and buckling of the infrastructure built on the expansive soils and can result in billions of dollars of damage annually.
To mitigate the effects of expansive soils Geotechnical engineers have had the option to remove expansive materials from structural areas and replace them with non-expansive imported material or mechanically stabilize the expansive clay by over-optimizing the moisture during compaction. Both of these methods have inherent limitations-- the practice of export/import has become cost prohibitive in today's economy, while environmentally it's disruptive to the surrounding communities and exhausts the minimal resources that are available. Mechanically stabilizing the expansive clay by over-optimizing the moisture content leads to issues of lower compaction and does little to reduce the continual fluctuation of moisture content in the future.
The depletion and cost of quality construction materials for engineering applications continually confronts material engineers and designers. Even if good quality construction materials are available, the cost and environmental impact of transporting these materials have begun to preclude their use.
To address these economic and environmental realities, designers and engineers have turned to chemical stabilization as a method to increase the bearing capacity of native soils used both in shallow and deep foundation support. Chemical treatment of non-cohesive or unstable soils with a cementitious stabilizer creates engineering benefits that result in increased bearing strength and durability.
Dependent on soil type and percent of stabilizer, strength gains can develop above 1,000 psi, although most foundation support applications would only require unconfined compressive strength of less then 300 psi.
To achieve low permeability, the voids and pore spaces in a material should be minimized or filled. Compacted clay has a low permeability, but lacks the other desirable properties of a suitable structural section - compressive strength and durability. Chemical soil stabilization brings improved strength and durability without sacrificing the impermeability associated with clays.