Abstract: The dispersity of dispersive clay in water is essential for the erosion and piping damage of dikes, channel slopes, and road slopes in dispersed land areas, and the discrimination of soil dispersion is prerequisite for engineering construction in dispersed land areas. In this paper, the tests such as pinhole test and crumb test are conducted to determine the dispersity of soil samples, then scanning electron microscope and X-ray diffraction are carried out to study the dispersion mechanism and microstructure of dispersive clay, and the primary and secondary influencing factors of soil dispersion are analyzed. Because of the strong linear relationship between the standard hygroscopic moisture content and the montmorillonite content of soil mineral composition, the distribution characteristics of montmorillonite content and pH value of typical dispersive clay are summarized by big data, a comprehensive discrimination method of soil dispersion based on the standard hygroscopic moisture content + pH value test is proposed, and the corresponding discrimination indices and discrimination procedures are given. Finally, it is verified with an engineering example. The results show that the existing environment with certain montmorillonite content and high pH value is the material basis and environmental guarantee for the dispersity of soil mass. If the requirements of montmorillonite content ≥ 10% and pH ≥ 8.5, the soil can be judged as dispersive clay; for soils out of this range, soil dispersity should be comprehensively judged in combination with the determination of dispersity of soil and field investigation results.

Key words: dispersive clay, dispersion mechanism, montmorillonite, standard hygroscopic moisture content, pH value