A new approach for identification of dispersivity class of soils by combining physical and chemical tests

Abstract

The safety and performance of embankment dams after impounding water are highly related to the characteristics of the selected dam material. Impermeability is achieved by using clay soils as the core material in embankment dams. It has been observed that there are many collapsed dams, especially when dispersive soils with very low internal erosion resistance are used in the impermeable zone. For this reason, such soils should be determined at the design stage and not used in the construction of embankment dams. The dispersion mechanism is known to be controlled by clay mineralogy and cations in the pore fluid of soil. The physicochemical behaviour of the clay-water system is crucial to clarify the dispersion mechanism. Physical and chemical tests used for determining the dispersibility potential of soils are extensive and time-consuming methods. An alternative method has been proposed within the scope of this study. Three user-friendly and practical models based on Gene Expression Programming (GEP) were produced using chemical and double hydrometer test results to predict dispersion percentage (D%). In addition, a new classification criteria was proposed to identification of dispersivity class based on pinhole test data. If the dispersion percentage is less than 12% is soil is classified as non-dispersive, the dispersion percentage is between 12% and 30% and greater than 30%, it is defined as intermediate and dispersive, respectively. With this proposed criterion, more consistent and successful results were obtained for the dispersivity class.