The Role of Anions in the Dispersion Potential of Clayey Soil

Soil dispersion is a phenomenon where soil particles float when they are exposed to water and are carried away by the force of seepage. Various laboratory methods, including double hydrometer, Emerson, and pinhole tests and the Sherard chemical method have been used to evaluate soil dispersion potential. Despite the fact that soil dispersion is caused by its chemical composition, the results obtained from the chemical methods, especially from the Sherard method, do not match the results of the pinhole test. In this study, the role of existing anions in the dispersion potential of clayey soils was studied. Natural soil samples were collected from different regions of Iran and artificial soil samples were created by adding different percentages of sodium chloride, sodium carbonate, sodium sulfate, and sodium polyphosphate to a non-dispersive soil. The physical, chemical, and index properties of all samples were determined and the Sherard method and pinhole test were employed to determine the dispersion potential. The results obtained from the tests showed that soil dispersion, which is a physico-chemical phenomenon, was caused by a combination of existing anions and cations in the soil, both in type and quantity. It was also found that the Sherard chemical method did not determine soil dispersion correctly since the role of some anions, especially chloride, was neglected. Among the existing anions in the soil, chloride, as opposed to sodium, acted as a flocculating factor.