Effects of particle morphology on pore structure and soil water retention behaviors of granular soils

Given grain size distribution (GSD) and relative density, the SWRC of granular soils can be straightforwardly predicted. However, the evolution of SWRC with different particle morphologies under the same GSD is still unclear. To solve this fundamental problem, herein, four sand analogs with different particle shapes under the same GSD were produced by 3D printing. The SWRCs and the pore structure at mesoscale were synergetically measured by using nuclear magnetic resonance (NMR) technology and HYPROP water potential meter. The relationship between particle morphology and SWRC was quantitatively analyzed, and the soil pore structure evolution under different particle morphology was clearly observed. Compared with round particle shape soils, soils with the same GSD but higher degree of angularity were found to have a subtle higher air entry value at a given relative density, even though the global void ratio is larger. NMR results indicate the pore structure of specimens with different particle morphology is similar. The pore volume is increased with angularity while the maximum pore throat shows an opposite trend. The difference in maximum pore throat is the fundamental reason for the variation in air entry value, highlighting the importance of particle morphology on soil water retention behaviors.