Abstract: Clay content is a key factor in evaluating soil dispersibility, but few previous studies are found in literature of the dispersive mechanism of low clay content loess. This study evaluates the dispersibility of such soil－collected from Guyuan, Ningxia－using five commonly used methods and a comprehensive evaluation method. We examine the factors of soil dispersibility and its mechanism through mineral composition, microscopic morphology, and chemical analysis. The results indicate that the comprehensive evaluation of different methods reveal this low-clay-content loess as a dispersive soil. The exchangeable sodium percentage of this soil is quite low, implying its dispersion mainly results from the physical factors instead of chemical factors. The bonding effect of aggregates cemented by clay particles and the aggregate structures agglomerated by aggregates are both weak due to low clay contents. Therefore, we develop a physical dispersive mechanism for low clay content loess: under the action of water, non-water-stable aggregates formed by the cementation of clay particles quickly disintegrate, leading to an increase in soil pores or certain changes in pore structure, i.e., erosion and similar phenomena.

Key words: hydraulic engineering, low-clay-content loess, dispersibility, particle aggregation, physical dispersion