The effect of particle size distribution and shape on the microscopic behaviour of loess via the DEM

Loess has a loose metastable structure, which is not difficult to destroy under loading. As the core of loess structures, the current main research directions of loess engineering properties are studying their microscopic behaviours and then interpreting and predicting macroscopic mechanical properties. In this study, based on the analysis of the basic physical properties of loess samples from seven different places, each sample is scanned using X-ray with continuous slice computed tomography (CT), and the three-dimensional microstructure of loess samples is established. According to the computer graphics method, each particle is equivalent to an ellipsoid, and the flattening rate and elongation rate of particles in each sample are quantitatively counted. Taking the particle size distribution (PSD) and shape parameters (flatness and elongation) of each sample as the control factors for generating discrete element method (DEM) samples, a series of triaxial compression simulation tests are conducted, and the microscopic behaviours of each sample are studied within the entire test framework. Comparing the results of seven different samples, it is shown that both PSD and particle shape have effects on the stress–strain relationship, dry density and normal contact force of loess samples. Most of the sand particles (> 0.075 mm) are flat particles, while the clay particles (< 0.005 mm) are mainly near spheres. When the volume fraction of sand particles is large, the dry density of the sample is the lowest. However, when the content of near-spherical clay particles is large and the PSD is good, the average coordination value is large, which shows that it has a strong normal contact force and thus a higher shear strength.