DEM analysis of the influence of the intermediate stress ratio on the critical-state behaviour of granular materials

• Published in: Granular matter 2014-10, Vol.16 (5), p.641-655
• Main Authors: Huang, X., Hanley, K. J., O’Sullivan, C., Kwok, C. Y., Wadee, M. A.
• Format: Article
• Language: English
• Subjects: Complex Fluids and Microfluidics; Computer simulation; Constants; Discrete element method; Engineering Fluid Dynamics; Engineering Thermodynamics; Failure; Failure analysis; Foundations; Geoengineering; Granular materials; Heat and Mass Transfer; Hydraulics; Industrial Chemistry/Chemical Engineering; Materials Science; Original Paper; Physics; Physics and Astronomy; Soft and Granular Matter; Stress ratio; Stress state; Stresses; Three dimensional; Void ratio
• ISSN: 1434-5021; 1434-7636
• DOI: 10.1007/s10035-014-0520-6

The critical-state response of granular assemblies composed of elastic spheres under generalised three-dimensional loading conditions was investigated using the discrete element method (DEM). Simulations were performed with a simplified Hertz–Mindlin contact model using a modified version of the LAMMPS code. Initially isotropic samples were subjected to three-dimensional stress paths controlled by the intermediate stress ratio, b = [ ( σ 2 ′ - σ 3 ′ ) / ( σ 1 ′ - σ 3 ′ ) ] . Three types of simulation were performed: drained (with b -value specified), constant volume and constant mean effective stress. In contrast to previous DEM observations, the position of the critical state line is shown to depend on b . The data also show that, upon shearing, the dilatancy post-peak increases with increasing b , so that at a given mean effective stress, the void ratio at the critical state increases systematically with b . Four commonly-used three-dimensional failure criteria are shown to give a better match to the simulation data at the critical state than at the peak state. While the void ratio at critical state is shown to vary with b , the coordination number showed no dependency on b . The variation in critical state void ratios at the same p ′ value is apparently related to the directional fabric anisotropy which is clearly sensitive to b .