Evolutions of Fabric and Contact Forces of Granular Materials Under Continuously Varying b Value Using DEM
The b value [\(= (\sigma_{2} - \sigma_{3} )/(\sigma_{1} - \sigma_{3} )\) ] has been used to illustrate the influence of intermediate principal stress σ2 on the major and minor principal stresses, σ1 and σ3, respectively, on the macroscopic as well as the
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Abstract The b value [¼ ðr2 r3 Þ=ðr1 r3 Þ] has been used to illustrate the influence of intermediate principal stress σ2 on the major and minor principal stresses, σ1 and σ3, respectively, on the macroscopic as well as the micromechanical behaviors of granular materials under general stress systems. The anisotropic characteristics of fabric and contact forces have been used to describe the micromechanical behaviors of granular materials. However, most related studies were conducted under constant b value stress paths. The objective of this paper is to study influences of the b value on the evolutions of fabrics and contact forces of granular materials under continuously varying b value stress paths, using the Discrete Element Method (DEM). To this end, the six continuously varying b value stress paths were simulated in this study. The stress-controlled method with constant mean stress 100 kPa on 8000 spheres was conducted. This study found that changing the b values continuously show different distributions of the fabric and contact forces evolutions. The increments of anisotropy coefficients of fabric, normal contact forces, and tangential contact forces differ depend on the b value. However, the differences in the directions of stress paths do not affect those anisotropy coefficients at the peak stress.
1 Introduction Granular materials such as sand or gravel are a setup of discrete particles with contact forces interacting at the contact points between them when shearing is applied. In particular, shearing deformation of the granular assembly causes change D. Phusing (&) P. Srirat Department of Civil Engineering, Faculty of Engineering at Sriracha, Kasetsart University Sriracha Campus, 199 Tungsukhla, Si Racha 20230, Chonburi, Thailand e-mail: [email protected] K. Suzuki Department of Civil and Environmental Engineering, Saitama University, Saitama 338-8570, Japan © Springer Science+Business Media Singapore 2017 X. Li et al. (eds.), Proceedings of the 7th International Conference on Discrete Element Methods, Springer Proceedings in Physics 188, DOI 10.1007/978-981-10-1926-5_10
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in the magnitude of contact forces, in the number of load-carrying contacts, distribution of contact forces, and contact orientation at the particle level. The micromechanical aspects from microscopic parameters to macroscopic behaviors have been researched to describe the particle mechanism with physical model experiments [1, 2] as well as with the numerical simulations using Discrete Element Method (DEM) [3–5]. A non-dimensional parameter b ¼ ðr2 r3 Þ=ðr1 r3 Þ by Habib [6] where σ1, r2 , and r3 are major, intermediate and minor stresses, respectively. The b value is an intermediate stress ratio describing the influence of intermediate stress r2 in the general stress system. Several experiments and simulations had been conducted to study the influence of r2 on the macro behavior of sand among different stress paths. It was concluded that the macro behavior differs depending on the b value (e.g
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