Discrimination methods for dispersivity of fine-grained soils based on dispersive mechanisms

The crumb tests, the pinhole tests, the double-hydrometer tests, the pore water soluble cation tests and the exchangeable sodium ion percentage tests are the common methods for identifying the dispersivity of the fine-grained soils, which are complex and time-consuming. Based on the dispersive mechanisms of the fine-grained soils, the soil samples with different clay contents and sodium carbonate mass fractions are prepared artificially to analyze the suitability of the conventional discrimination methods for dispersivity and to propose a rapid and accurate discrimination method. The results show that the dispersive soils can be divided into physical dispersive soils which can be called low cohesive soils, chemical dispersive soils and physical-chemical composite dispersive soils. It also can be found that 10% of the clay content is the upper limit of physical dispersivity of the fine-grained soils. The mud ball tests, the pore water soluble cation tests and the exchangeable sodium ion percentage tests can be applied to all fine-grained soils, and the pinhole tests and the double-hydrometer tests are suitable for the fine-grained soils with a clay content no lower than 10%. The results of the mud ball tests should be used as the discrimination criterion for dispersivity if the clay content is lower than 10%, otherwise the discrimination criterion for dispersivity should be the strongest dispersivity results of the mud ball tests and the pinhole tests. The double-hydrometer tests, the pore water soluble cation tests, the exchangeable sodium ion percentage tests, and the pH tests are used as the explanatory tests for the dispersive mechanisms of the fine-grained soils, which have no influences on the comprehensive discrimination.