A unified expression for grain size distribution of soils

Publication date: 15 February 2017
Source:Geoderma, Volume 288
Author(s): Li Yong, Huang Chengmin, Wang Baoliang, Tian Xiafei, Liu Jingjing
Grain size distribution (GSD) is fundamental for soils and usually described by a set of graphic parameters (e.g., median size, kurtosis, skewness, uniform and curvature coefficient). Some probability distributions (e.g., lognormal and Weibull distribution) are used for special cases, but no general expression is available. In this paper we propose a general distribution form of P(D)= CD ^{− μ}exp(− D/D c) for various soil materials, with P(D) the exceedance percentage and C, μ and D c are parameters determined by the grain size frequency data. The power-law and exponential part of this expression respectively responds to the self-similar and random processes of grain fragmentation and accumulation in soil generation and evolution. The GSD parameters are distinct in soils and their variation reflects the changes in grain composition, such as the grain migration and segregation in landslides, avalanches, debris flows and sedimentary deposits. In addition, the GSD also fits the pore size of granular materials, confirming the grain-pore duality and suggesting an important role of the GSD expression in dynamics of soils and granular media in general.