Numerical investigation of compaction effects on pore structure and hydraulic properties of fluid-saturated granular materials

Since there is no doubt that soil compaction can induce substantial changes in the soil properties, affecting all kinds of physical, chemical, and biological processes in soils, it is worth some effort to attempt to characterize these changes quantitatively [1]. Soil properties, such as its permeability and hydraulic conductivity or the pressure-saturation relations, to name a few, are closely related to the pore space geometry, in particular to the pore size distribution (PSD). Future progress in incorporating the soil hydraulic properties in the modeling studies related to soil compaction will require, among others, an enhanced understanding of how PSD evolves during the compaction process. In addition to much-needed experimental observations, we believe that a significant part of this endeavor should be devoted to making use of the available pore-scale numerical techniques.

We will focus on the approach based on obtaining the pore structure in between the grains (of idealized grain geometries) for given porosity and particle size distribution. In this study, we use the discrete element method (DEM) [2] to obtain the evolution of pore structure by simulating the movement of grains during the compaction process, for a variety of sphere packings (mono-sized particles and binary mixtures, to start with). For this purpose, we use the open-source platform Yade-DEM [3]. The hydraulic properties of the fluid-saturated granular materials are simulated with the pore-scale finite volume (PFV) model [4]. Also, we use a combination of regular Delaunay facets and regular Voronoi vertices to extract the geometry of the pore structure. The effects of compaction on the pore structure and the hydraulic properties of different spherical packings will be discussed.

 

References:

[1] Mahmoodlu, M. G., Raoof, A., Sweijen, T., & Van Genuchten, M. T. (2016). Effects of sand compaction and mixing on pore structure and the unsaturated soil hydraulic properties. Vadose Zone Journal, 15(8).

[2] Cundall, P.A., and Strack, O.D.L. (1979) A Discrete Numerical Model for Granular Assemblies. Geotechnique, 29, 47-65.

[3] V. Šmilauer et al. (2021), Yade Documentation 3rd ed. The Yade Project. (http://yade-dem.org/doc/)

[4] Chareyre, B., Cortis, A., Catalano, E. et al. (2012). Pore-Scale Modeling of Viscous Flow and Induced Forces in Dense Sphere Packings. Transp Porous Med 92, 473–493.