SANISAND: Simple anisotropic sand plasticity model Taiebat, Mahdi; Dafalias, Yannis F.
International journal for numerical and analytical methods in geomechanics,
10 June 2008, Volume:
32, Issue:
8
Journal Article
By means of the three-dimensional discrete element method, we study the long-time evolution toward liquefaction state in granular materials composed of spherical particles under multidirectional ...cyclic shearing at constant volume. Extensive simulations were carried out along 1-D linear, 2-D linear, circular/oval, and 8-like shear paths, and the evolution of the system was analyzed in terms of pore pressure, shear strain, and granular texture. The macroscopic stress path and stress–strain response agree well with laboratory experiments. We find that the liquefaction resistance, i.e., the number of cycles necessary to reach the liquefaction state, is generally lower under multidirectional loading as compared to unidirectional loading. As the transient vanishing of mean stress does not occur for all stress paths, we introduce a shear strain-based liquefaction criterion that can be consistently applied to all strain paths. The granular texture is monitored through the coordination number, particle connectivity, force and fabric anisotropies, and friction mobilization. In particular, a particle-void descriptor, named centroid distance, is found to be closely related to the shear strain accumulation. We show that the force anisotropy tensors become almost proportional to the deviatoric stress tensor more quickly than the fabric anisotropy tensor, which takes most of the pre-liquefaction period to follow the external loading. The relationship between deviatoric stress ratio and the force and fabric anisotropies, known to hold in monotonic triaxial loading, also holds with high accuracy in the studied multidirectional cyclic shearing paths; the contributing weights of the anisotropies level off in the post-liquefaction period and do not depend on the shear path.
This study investigates the cyclic liquefaction resistance of granular materials under non-hydrostatic consolidation using 3D discrete element method (DEM) simulations. The study specifically ...examines how various sample preparation techniques affect the cyclic liquefaction resistance of polydisperse spherical particle samples with a Kc value of 0.5, where Kc represents the ratio of initial horizontal to vertical normal stresses. The results reveal that the choice of sample preparation technique significantly affects the cyclic liquefaction resistance of the samples. Furthermore, this study explores the inherent fabric of the samples using coordination number and contact-normal fabric anisotropy, and demonstrates that it plays a critical role in controlling the cyclic liquefaction resistance of granular materials under nonhydrostatic consolidation. The study emphasizes the significance of considering the inherent fabric in understanding the behavior of granular materials under non-hydrostatic consolidation. This can inform the design of experiments and the development of constitutive models to explore the interplay between sample preparation techniques, fabric anisotropy, and cyclic liquefaction resistance.
We use three-dimensional particle dynamics simulations to investigate the microstructure evolution of granular material subjected to isochoric cyclic shearing, driving the system to a liquefaction ...state. The cyclically sheared assembly presents a realistic macroscopic response as observed in physical experiments. By analyzing the contact network evolution in the post-liquefaction period, we show that the onset of liquefaction state is characterized by a sudden drop of coordination number and a fragile particle connectivity network. The simulation suggests a critical coordination number for exiting the liquefaction state. Evolution of fabric anisotropy combined with coordination number implies the isotropic and anisotropic gain or loss of contacts at certain durations of a post-liquefaction loading cycle.
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