Enhancing soil stability: using plant extracts to modify cation exchange capacity in expansive soils

Expansive soils are recognized as problematic in the construction industry due to the presence of specific clay minerals that exhibit significant volume changes upon moisture variation. When these minerals come into contact with water, ionic interactions involving cations and anions activate the swelling behavior of the soil. Among various soil improvement techniques, soil stabilization remains one of the oldest and most widely adopted methods by engineers and geotechnical professionals. This paper introduces an innovative, environmentally sustainable approach that integrates soil and plant chemistry, leveraging the cation exchange capacity (CEC) of soil and the properties of biological plant extracts. CEC refers to the soil's ability to adsorb and exchange positively charged ions (cations). When the availability of free cations is limited, the soil's exchange capacity reduces, which can lead to a form of natural stabilization. CEC can be assessed through various techniques, with the methylene blue spot test being a preferred method due to its simplicity, cost-effectiveness, and rapid execution. Plant-based extracts, rich in anions, can interact with soil cations, effectively neutralizing their effects and contributing to stabilization and strength enhancement. This geobiological stabilization method has demonstrated promising results in terms of cost efficiency and applicability. It offers potential for use in highway embankment slope stabilization, subgrade improvement, forest conservation efforts, and broader ecological preservation initiatives.