Numerical Identification of the Critical Particle Size for Skeletal Fractions in Fractal‐Graded Soils

ABSTRACT Internal stability is an important attribute for granular soils in assessing the sensitivity to suffusion. The particle composition of soil matrix can be used to establish the internal stability criterion. Overviews of current researches on the soil skeleton, the critical particle size for the skeletal fraction is unclear and inadequate, especially for soil matrix with significant fine contents. The content of erodible particles cannot be accurately determined to assert the internal unstable. In this article, a new formula for identifying the critical particle size of soil matrix with a particular particle size distribution is derived analytically. The soil particles are separated into filling and skeletal fractions based on their influence on the matrix volume. A modified experimental method is designed to investigate the separation point of particle fractions using the discrete element numerical simulation. The results indicate that the critical particle size of fractal‐graded soil can be expressed as a function concerning particle size ratio and fractal dimension. Particles larger than the critical particle size belong to the skeletal fractions, the remaining particles are the filling fractions that implicate the potential erodible particles in suffusion. A new geometrical criterion is proposed to evaluate whether soil matrix is overfilled by filling fractions based on the critical mass ratio rather than conventional fine content thresholds, which demonstrates broader applicability across widely graded soils. This study will facilitate further research on the internal stability of graded soils, the design of filter layers, and establishing a unified criterion for assessing the sensitivity to suffusion.