Quantifying the influence of grain morphology on sand hydraulic conductivity: A detailed pore-scale study

Abstract

This paper presents a detailed study to quantify the influence of grain morphology on sand hydraulic conductivity aided with pore-scale analysis. One hundred and twenty-nine numerical models of Leighton Buzzard sand and Jordan sand were simulated to obtain the flow characteristics, and Matlab code was developed to quantify their pore characteristics. The influence of grain morphology on sand hydraulic conductivity was analyzed using eight grain morphological descriptors, five permeability parameters, and six pore indexes. The results show that the grain morphology affects the specific surface, porosity, and flow tortuosity through the sand, which influences its hydraulic conductivity. The Kozeny-Carman equation well predicts sand hydraulic conductivity but the Ckc in this equation is not a constant and correlates strongly to hydraulic tortuosity. Sand containing grains that are less platy and less concave tend to have an isotropic sand pore/throat structure that associates with a lower Ckc. From the pore-scale perspective, hydraulic conductivity is highly affected by the D50 pore size, which is strongly related to the sand specific surface and porosity. More concave and less spherical grains tend to form more porous sand. Platy and concave grains tend to have a larger variation coefficient and smaller mean in the sand pore and throat sizes, causing a lower sand hydraulic conductivity. These quantitative analyses shed light on the role of grain morphology in affecting the characteristics of the sand pores and throats, and their effect on sand hydraulic conductivity.