Study of the Factors Influencing Diffusive Tortuosity Based on Pore-Scale SPH Simulation of Granular Soil

Abstract

Tortuosity quantitatively reflects the complexity of porous media. For the diffusion process in porous media, diffusive tortuosity is inevitably an important research topic. A simulation experimental method is proposed to study diffusive tortuosity in granular soil based on 3D pore-scale simulation by smoothed particle hydrodynamics (SPH). On the basis of the simulation results, the relationships between diffusive tortuosity and microstructural parameters are discussed. Simulation experiments are implemented on 3D granular soil columns generated by PFC software and soil layers formed by periodic expansion of the soil columns. The accuracy of the pore-scale SPH diffusion model is verified by the analytic solution for the particular case of a pure water column. The results show that the dimensionality does affect the diffusive tortuosity. 2D profiles cannot represent the original 3D medium in terms of the diffusion characteristics. Within the limited range of the variation of porosity during soil compression, the relationship between porosity and diffusive tortuosity can be considered to be linear. In addition, for the case of uniform granule size, diffusive tortuosity is almost linearly related to the specific surface area. Tortuosity values for soil columns are larger than those for the soil layer, which denotes that the effect of the sidewall on diffusion cannot be overlooked for a centimeter-scale soil column.