Abstract: Grain size distribution, grain shape, and filling density are the critical factors that affect the pore structure and permeability of coarse-grained soil. However, only a few studies have examined the effect of grain shape on the permeability of coarse-grained soil. The main reasons are that it is not easy to quantitatively describe the grain shape and to study its influences on pore system characteristics. This study compares the pore system characteristics and permeability of samples filled with irregular gravels, spherical and regular octahedral grains, respectively. The grain shape was quantified by the length-width ratio and roundness obtained in the previous study. The images of internal structure for samples were obtained by the computed tomography (CT) scanning, and then the specific surface area was obtained for reconstructed three-dimensional (3D) pore structure of samples. The results indicate that the specific surface area is a reliable parameter to identify the pore structure characteristics of coarse-grained soil. For samples with the same grain size distribution and porosity, the specific surface area of the pore system decreases as grain roundness increases and grain shape approaches sphere. The hydraulic conductivity results show that for these samples, the hydraulic conductivity increases with the increase of grain roundness but the decrease of the specific surface area of pore system. The samples filled with spherical grains have the highest permeability. The samples filled with the more nonspherical grains contain pore systems with more resistance to seepage flow and are less permeable.

Key words: grain shape, CT scanning technique, pore system, specific surface area, hydraulic conductivity