A new multiscale Cosserat model for size effect simulation in granular media

The Cosserat continuum, which contains a length scale factor l reported to link with the material’s grain size, is seemingly reasonable to describe the size effect of granular media. However, the physical meaning of l is still unclear, and its potential in describing the size effect is seldom studied. In this work, the performance of the conventional Cosserat model in capturing the size effect of granular media is firstly assessed. A new multiscale Cosserat constitutive model with an additional higher-order internal length scale vector Dq is then proposed based on the conventional Cosserat theory. The advantage of the proposed multiscale Cosserat model in size effect simulation for granular media is discussed through numerical simulations of centrifuge slope experiments and triaxial compression tests. The analysis results denote that the multiscale Cosserat continua are more sensitive to size effect than the conventional Cosserat continua, and the length scale vector Dq is like a symmetry-breaking factor that can trigger asymmetric deformation in structures; the influences of length scale factor l and Dq are seemingly opposite on stress concentration. This subtly improved constitutive model has the potential to simulate the size effect of a wider variety of materials.