Micromechanics of fine-grain infiltration in coarse grain sands

The loss of fine particles can induce mechanical instabilities in granular soils subjected to internal fluid flow. An appealing countermeasure consists of the re-injection of fine grains with the objective of achieving retention in the soil matrix. In this study, both gravity- and fluid-driven infiltration of fine particles into coarse-grain columns with different solid fraction \(\phi\) and size ratios R have been studied using coupled pore-scale finite volume (PFV) and discrete element method (DEM) schemes. Three clogging regimes, surface clogging, deep infiltration, and percolation are detected, and the characteristic infiltration depths \(L_{0}\) are found to grow exponentially with R under gravity- and fluid-driven cases. A probabilistic model derived from pore-constriction size statistics is then put forward, which could efficiently interpret the decaying distribution of fine retention for a given size ratio R and packing density. The mean transit velocity of fine grains follows an increasing trend with R under fixed \(\phi\) and can be collapsed over an almost constant value with the appropriate scaling of \(\phi /\sqrt{R}\). Compared to gravitational percolation, more lateral dispersion is found in fluid-driven conditions, and an estimation of the related lateral dispersion coefficient D is provided based on \(\phi\) and R.