Effects of particle shape and size distribution on hydraulic properties of grain packs: An experimental study

TL;DR

This experimental study investigates how particle shape and size distribution influence the hydraulic properties of grain packs, providing new empirical data and validating the critical path analysis method for estimating saturated hydraulic conductivity.

Contribution

It offers the first comprehensive experimental comparison of particle shape effects on pore space fractal dimension and hydraulic conductivity in grain packs.

Findings

DMCC varies with particle shape and size distribution

CPA accurately estimates SHC within a factor of four

Particle shape significantly affects pore space fractal dimension

Abstract

Uniform and multi-dispersed grain packs have been frequently used to conceptually study flow in porous media. Numerical simulations were previously used to address the effect of particle shape on characteristics, such as pore space fractal dimension, moisture characteristic curve (MCC) and saturated hydraulic conductivity (SHC) of grain packs. However, experimental observations are still required since fractal-based approaches have been extensively proposed to model various properties in porous media. In this study, 16 angular sand and 16 spherical glass bead samples with different particle size distributions (PSDs) from well- to poorly-sorted were packed. The MCC was measured using the combination of sandbox and pressure plates methods. The pore space fractal dimension (DMCC), calculated from the measured MCC, ranged from 0.80 to 2.86 in sand and from -0.18 to 2.81 in glass bead packs, which indicated that DMCC may be negative in homogenous media (e.g., glass bead packs) consistent with several studies in the literature. Results showed greater DMCC for the sand packs than the glass bead packs with the same geometric mean diameter values and PSDs. This clearly demonstrated the effect of particle shape on DMCC in the studied packs. The critical path analysis (CPA) approach was used to estimate the SHC measured using the constant-head method. We found that the CPA estimated the SHC accurately, within a factor of four of the measurements on average. Although the CPA is theoretically known to be accurate in media with broad pore size distributions, we experimentally found that it estimated the SHC in various types of grain packs reasonably well.