Micromechanical analysis of the cyclic mechanical response of granular materials through DEM simulations

¹ Center for Geotechnics, Technical University of Munich, 81245 Munich, Germany
² Civil Engineering Department, University of Applied Sciences Potsdam, 14469 Potsdam, Germany

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Published online: 1 December 2025

Abstract

In this study, we investigate with the Discrete Element Method (DEM) the mechanical behavior of a cohesionless granular material under undrained true triaxial conditions, considering both monotonic and cyclic loading. We link the microstructure evolution within the granular assembly to its macroscopic cyclic response. To capture the mechanical response of our reference material (Karlsruhe fine sand), a rolling resistance linear contact model along with spherical particles is calibrated through a trial-and-error process, adjusting the model parameters to capture the experimentally observed behavior as close as possible. A series of cyclic undrained triaxial tests were simulated to investigate the micromechanical processes underlying liquefaction of sand under cyclic shearing. We analyzed the evolution of various fabric indices, including the redundancy index, contact normal orientations, and fabric anisotropy in relation to the pre- and post-liquefaction responses. The results reveal that a redundancy index below unity provides a unified criterion for the loss of the isostatic condition within the granular assembly, which triggers the onset of liquefaction. Throughout the cyclic loading process, sliding-dominant contact-yielding mechanisms remain prevalent. Additionally, significant changes in contact normal orientation and increasing fabric anisotropy dependent on the induced axial strain occur as the sample undergoes post-liquefaction deformation.