DEM Modeling Mechanical Behavior of Unsaturated Structural Loess under Constant Stress Increment Ratio Compression Tests

Abstract

This paper presents a numerical investigation into the macromechanical and micromechanical behavior of unsaturated structural loess under constant stress increment ratio compression using the distinct-element method (DEM). Loess is typically a kind of clayey silt with a metastable structure composed of interparticle bonding and large voids. To represent the interparticle bonding, a published bond contact model proposed by the authors was used. Three samples with different water contents were tested under six incremental stress ratios to study the influence of water content and stress increment ratio on the mechanical response of loess. The DEM results qualitatively agree with available experimental observations in the literature. The observed macromechanical properties can be explained by the velocity field, force-chain distribution, bond breakage events, and contact orientation at the microscopic scale. When the stress increment ratio is low, the force chains exhibit a column-like pattern. As the stress ratio increases, bond breakage occurs uniformly and the force chains form a web-shaped pattern. As the water content increases, the force chains become denser and the number of broken bonds becomes larger. The compression and shear behavior of the specimens is related to the bond breakage at the microscopic scale. The main failure types are tension failures in the stress range studied irrespective of the stress increment ratio. The proportion of tensile failures increases with an increase in water content. In addition, the contact orientations and deviator fabrics of contacts are also studied.