Hydromechanical model for internal erosion and its relationship with the stress transmitted by the finer soil fraction

We present a theoretical model to determine the hydromechanical boundary of an internally unstable soil subject to vertical seepage. The model is based in momentum balance equations, which consider that the system is divided into three components: water, finer soil fraction, and coarser soil fraction. The parameters of the model are as follows: the effective stress, the porosity of the soil, the friction angle between the coarse and fine fractions, and the proportion of the effective stress that is transmitted to the finer fraction (G*). Using laboratory data collected on a large permeameter, we demonstrate that the model is able to properly describe the observed behavior. Furthermore, we show that the value of G* is related to the value of D₁₅′/d₈₅′ proposed by Kezdi (Soil physics—selected topics. Elsevier, Amsterdam, 1979) and that it has the same trend as found experimentally by Skempton and Brogan (Geotechnique 44:449–460, 1994). The proposed model is a promising method to deduce an approximate value of critical hydraulic gradient that triggers internal erosion in a cohesionless soil of known particle size distribution curve.