Predicting the hydraulic properties of Zbraslav sand, as affected by compaction

Zbraslav sand has been used as a testing material in many former soil mechanics studies. It is a poorly graded sand with almost no fines and with grains of subangular shape. We will be interested in predicting the variation of its pore structure, in particular the pore size distribution (PSD), as a result of the oedometric compaction of the sample. Apart from the derived unsaturated hydraulic properties, we will be particularly interested in predicting its saturated permeability with respect to non-Newtonian (shear-thinning) fluids.

Clarifying and quantifying the dynamics of the PSD due to compaction will be a difficult undertaking owing to the instability of soil structure and variation of PSD over time. In this study, we will follow the discrete approach during the sand compaction process introduced by Mahmoodlu et al. [1] and later studies. Discrete element method (DEM) can directly trace the motion of individual particles and explicitly consider the particle–particle interactions without the need of macroscopic constitutive correlations. We will use this method to generate a packing of idealized particles for a certain porosity and particle size distribution, and simulate the movement of grains during the compaction process. Subsequently, having the simulated configuration of grains at each observed state, the pore network will be extracted to obtain the pore connectivity and morphology [2]. In the next step, the flow of various shear-thinning fluids through the media (the pore network) will be simulated [3, 4]. In this way, we are preparing for a subsequent study focused on the experimental measurement of the effective PSD directly during the oedometric test. We are particularly interested in how the observed variations in pore structure will be represented by the effective PSD obtained by the method, introduced by Abou Najm et al. [5], i.e. computed from the observed permeabilities with respect to shear-thinning fluids.

This research is supported by Czech Science Foundation under grant 21-27291S.

 

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] Li, G. Y., Zhan, L. T., Hu, Z., & Chen, Y. M. (2021). Effects of particle gradation and geometry on the pore characteristics and water retention curves of granular soils: a combined DEM and PNM investigation. Granular Matter, 23(1), 1-16.

[3] de Castro, A. R., Agnaou, M., Ahmadi-Sénichault, A., & Omari, A. (2020). Numerical porosimetry: Evaluation and comparison of yield stress fluids method, mercury intrusion porosimetry and pore network modelling approaches. Computers & Chemical Engineering, 133, 106662.

[4] Hauswirth, S. C., Abou Najm, M. R., & Miller, C. T. (2019). Characterization of the pore structure of porous media using non‐Newtonian fluids. Water Resources Research, 55(8), 7182-7195.

[5] Abou Najm, M. R., & Atallah, N. M. (2016). Non-Newtonian fluids in action: Revisiting hydraulic conductivity and pore size distribution of porous media. Vadose Zone Journal, 15(9).