Three-dimensional microstructure characterization of loess based on a serial sectioning technique

Abstract

Loess has a loose metastable structure that easily collapses during wetting and loading. Microstructure analysis is essential for a better understanding of the engineering properties of loess; however, two-dimensional (2D) methods cannot fully demonstrate the geometric microstructural characteristics of loess particles. The three-dimensional (3D) loess microstructure is reconstructed based on an improved serial sectioning technique. Point, edge and face contacts are observed from the 3D reconstructed microstructure of natural loess. The 3D microstructural features of particles and pores are also quantitatively studied by analyzing statistical parameters, including the equivalent diameter, sphericity, aspect ratio and orientation index. The particle size distribution (>10 μm) obtained from the microstructural analysis is validated via a comparison with the results of a laser particle size analysis. In total, 92% of the particles have a sphericity that lies between 0.5 and 0.9, and the aspect ratio of 93% of the particles is between 0.3 and 0.7. Additionally, 67% of the particles are oriented from 0° to 45°, whereas approximately 64% of the pores (>2 μm) are oriented from 45° to 90°. Each 3D parameter has a unique value and can reflect the true spatial morphology of the particles, avoiding the influence of the observation angle and section. The 3D characterization of the loess microstructure will provide insights into the underlying collapse mechanisms and could provide realistic 3D parameters for use in numerical simulations.