Constitutive Modeling of Anisotropic Sand Behavior in Monotonic and Cyclic Loading

Abstract

An anisotropic plasticity model is proposed to describe the fabric effect on sand behavior under both monotonic and cyclic loading conditions within the framework of anisotropic critical state theory. The model employs a cone-shaped bounding surface in the deviatoric stress space and a yield cap perpendicular to the mean stress axis to describe sand behavior in constant mean stress shear and constant stress ratio compression, respectively. The model considers a fabric tensor characterizing the internal structure of sand associated with the void space system and its evolution with plastic deformation. The fabric evolution law is assumed to render the fabric tensor to become codirectional with the loading direction tensor and to reach a constant magnitude of unit at the critical state. In constant stress ratio compression, the final degree of anisotropy is proportional to a normalized stress ratio. An anisotropic variable defined by a joint invariant of the fabric tensor and loading direction tensor is employed to describe the fabric effect on sand behavior in constant mean stress monotonic and cyclic shear. A systematic calibrating procedure of the model parameters is presented. Satisfactory comparison is found between the model simulations and test results on Toyoura sand in both monotonic and cyclic loadings with a single set of parameters. The important role of fabric and fabric evolution in capturing the sand behavior is highlighted. Limitations and potential improvement of the model in describing cyclic mobility of very dense sand and sand behavior in nonproportional loading have been discussed.

Modelling the cyclic ratcheting of sands through memory-enhanced bounding surface plasticity

“…The parameter M appears in its traditional meaning of critical stress ratio under triaxial compression (directly related to the constantvolume friction angle). It should also be recalled that the assumption of unique critical state locus is still a matter of scientific debate, and certainly not the only option available -nonetheless, a several theoretical studies may be cited in its support (Li & Dafalias, 2011;Zhao & Guo, 2013;Gao & Zhao, 2015). An evolving version of the locus (Equation(3)) could be adopted in the future upon conclusive consensus on the subject -for instance, according to the path followed by Papadimitriou et al (2005).…”

“…TOWARDS A SANISAND MODEL WITH RATCHETING CONTROL While massive efforts have been devoted to modelling the undrained cyclic behaviour of sands, the cyclic performance under drained loading conditions has received far less attention. A few works tackled this issue by enhancing the bounding surface framework with fabric-related modelling concepts, such as Khalili et al (2005); Kan et al (2013); Gao & Zhao (2015); outside traditional bounding surface plasticity, the contributions by Wan & Guo (2001); Di Benedetto et al (2014); Liu et al (2014); Tasiopoulou & Gerolymos (2016) are also worth citing. However, none of the mentioned works focused explicitly on drained strain accumulation under a large number of loading cycles.…”

Dilatancy Relation for Overconsolidated Clay

“…In its present form, however, the dilatancy relation is unable to account for the influence of anisotropy on the mechanical behavior of clays (e.g., Ling et al 2002;Anandarajah and Dafalias 1986;Dafalias et al 2006). Its extension to account for anisotropy may be possibly made in conjunction with the recent progresses on anisotropic critical state theory (Li and Dafalias, 2012;Gao et al, 2014;Gao and Zhao, 2015;Zhao and Gao, 2016), which will be a future pursuit of the authors'. In addition, the dilatancy of clay in cyclic loading has been found dependent not only on the degree of overconsolidation but also shear strain accumulation (e.g., Ni et al, 2014;Kimoto et al, 2014).…”

Über ein elastoplastisches Stoffgesetz für zyklisch beanspruchten Sand

“…Zudem wird es kontinuierlich weiterentwickelt. Die neueste Entwicklungsstufe des Modells ist in der Lage, auch die Entwicklung der inhärent anisotropen Kornstruktur von Sand unter zyklischer Beanspruchung abzubilden . Dies gelingt, indem sowohl der Verfestigungsmodul als auch die Dilatanz als Funktionen eines dreidimensionalen Gefügetensors (engl.…”