Determination of the maximum diameter of free fines to assess the internal stability of coarse granular materials

Abstract

In granular soils, suffusion may occur only if three conditions are met: (i) the hydraulic gradient is high enough; (ii) the fine particles are not blocked by the constrictions of the larger ones; and (iii) the fine particles are free to move, i.e. they are not prevented to move by a steric condition. The aim of the paper is to determine the maximum diameter of the particles for the third condition, which are called the “free fines”. Three methods are examined: (i) the direct measurement of the bulk volume of binary mixtures of fine and coarse grains, (ii) the method proposed by Ghafghazi and Azhari in 2012 and (iii) a new method based on the calculation of the fine content for which the fines fill the voids between the coarse grains. Some methods, proved difficult to apply in practice, whereas the new method appeared consistent with the available experimental results. In particular, the method permitted to predict the results of flow tests carried out on binary mixtures of glass balls as well as gap-graded granular materials or materials with continuous grain size distributions.