Effects of Cyclic Rotation of Principal Stress Axes and Intermediate Principal Stress Parameter on the Deformation Behavior of Sands

SUMMARYThis study focuses on non-coaxial flow behavior of cohesionless soil undergoing cyclic rotational shear, with a special interest in the effects of particle-scale characteristics. To this end, we perform a series of 2D discrete element simulations with various particle shapes, inter-particle coefficient of friction, initial density, and stress ratios. The validity and efficacy of the numerical model is established by systematically comparing numerical simulation results with existing laboratory testing results. Such comparison shows that the numerical simulations are capable of capturing mechanical behavior observed in laboratory testing under rotational shear. We further demonstrate and quantify a strong yet simple relationship between the deviatoric part of the normalized strain increment and the non-coaxial angle, denoted by Δε ð Þ R q and ψ, respectively. This quantitative correlation between ψ and Δε ð Þ R q is independent of applied stress ratio, initial and current void ratio, and the number of cycles applied, but dependent on the principal stress orientation and particle-scale characteristics. At the same Δε ð Þ R q , specimens with higher inter-particle friction angle or smaller particle aspect ratio show greater non-coaxial angles. A simple model ψ ¼ 45 ∘ m Δε ð Þ R q is able to fit this ψ-Δε ð Þ R q relationship well, which provides a useful relationship that can be exploited in developing constitutive models for rotational shearing.

“…The development of strains for the same simulation is presented in Figure and is compared with the HCA pure rotation test results by Zhang et al . and Miura et al . .…”

Section: Validating the Numerical Results Via Simulation‐experiments Cmentioning

confidence: 88%

Section: Implementation Of Numerical Experimentsmentioning

confidence: 83%

“…Zhang et al . investigated the effects of intermediate principal stress parameter b ( b = ( σ 2 − σ 3 )/( σ 1 − σ 3 )). We choose the test results with b = 0.1 in Zhang et al .…”

Section: Validating the Numerical Results Via Simulation‐experiments Cmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Discrete element method analysis of non‐coaxial flow under rotational shear

Tong

Dafalias

et al. 2014

SANISAND‐FN: An evolving fabric‐based sand model accounting for stress principal axes rotation

Petalas

Dafalias

Papadimitriou

2018

Summary SANISAND is the name of a family of bounding surface plasticity constitutive models for sand within the framework of critical state theory, which have been able to realistically simulate the sand behavior under conventional monotonic and cyclic loading paths. In order to incorporate the important role of evolving fabric anisotropy, one such model was modified within the framework of the new anisotropic critical state theory and named SANISAND‐F model. Yet the response under continuous stress principal axes rotation requires further modification to account for the effect of ensuing noncoaxiality on the dilatancy and plastic modulus. This modification is simpler than what is often proposed in the literature, since it does not incorporate an additional plastic loading mechanism and/or multiple dilatancy and plastic modulus expressions. The new model named SANISAND‐FN is presented herein and is validated against published data for loading that includes drained stress principal axes rotation on Toyoura sand.

Upgrading SANISAND model to address continuous stress principal axis rotation: A conservative approach

Shahrokhi

Barani

2022

The SANISAND models are known for their ability to simulate sands behavior with various properties under a wide range of loadings. Nevertheless, there is much room for improvement in simulating stress principal axis (PA) rotation effects. This study tried to address the continuous stress PA rotation problem following a conservative approach in preserving the SANISAND basic formulation.The inelastic response of the material under the stress rotation is regulated by a plastic intensity index as a function of the stress rotation rate with respect to the deviatoric fabric tensor and the non-coaxiality between the stress and the plastic strain rate. The model performance is verified compared to the experimental data as well as other constitutive models. Supplementary discussions are provided to shed light on how fabric evolution results in a lower degree of anisotropy under continuous stress PA rotation. Based on continuum bounding surface plasticity, the proposed model addresses the fabric anisotropy effects on the severity of plasticity under continuous stress PA rotation.