DEM study on the non-coaxial deformation characteristics of granular soils under various traffic loading conditions

Abstract

Although the macro-scale stress–strain relations of sands under traffic loading can be investigated using hollow cylinder apparatus, the microscopic mechanism of the deformation accumulation and the non-coaxial behavior of sands under principal stress rotation induced by the traffic loading has not been fully understood. In this paper, both isotropic and transversely isotropic specimens comprised of elongated particles were generated using the discrete element method. The non-coaxial deformation characteristics of granular soils under various types of cardioid-shaped loading paths are illustrated in detail. The simulation results show that a greater cyclic vertical stress ratio and cyclic torsional stress ratio can lead to a smaller non-coaxial angle between the principal directions of stress and strain increment. The evolution of the internal structure is quantified by the contact-normal-based fabric tensor, which describes the load-bearing structure of granular specimens. The transversely isotropic specimen exhibits more significant non-coaxiality between the loading direction and the principal direction of the fabric and therefore greater volumetric contraction than that of the isotropic specimens. Moreover, the transversely isotropic specimen shows smaller normal strain accumulation than that of the isotropic specimen, which can be well explained by the interplay between the modulus of the specimen and the fabric evolutions.