Mechanical behaviour of a granular solid and its contacting deformable structure under uni-axial compression-Part II: Multi-scale exploration of internal physical properties

Following the previous companion paper, the proposed DEM model has been carefully validated and produced reasonable to good agreement with the corresponding laboratory experiments. This paper confidently probes the internal physical properties and extensively understands the multi-scale (macro-meso-micro scale) relationships in this granular system subjected to confined compression. The particle von Mises stress was proposed to effectively identify the direction and magnitude of strong force chains. Ring measurement cells were developed to calculate the spatial distributions of solid fraction, coordination number, friction mobilized factor, contact force vectors and stresses. The diagrams of contact force vectors were proposed to show the mechanism of force transmission onto the cylindrical wall. In addition, the statistical analyses for contact forces and mobilized friction were evaluated in this paper. Several key findings are highlighted as follows: (1) the force drop in the load-displacement response is attributed to some local reorganization of force chains; (2) the profiles of the contact force vectors transmitted onto the cylindrical wall match with those for macroscopic wall traction; (3) the contact force vectors on the cylindrical wall are mostly parallel with each other and make a specific angle with the horizontal, indicating the full friction mobilization on the cylindrical wall; (4) the inter-particle friction is more mobilized at the lower part than at the higher part during confined compression; (5) the radial, circumferential and vertical stresses within the bulk solid generally decay with depth in spite of some disorder; (6) The inter-particle and particle-wall contacts exhibit distinctive statistical patterns for contact forces and mobilized friction; (7) the mechanical response of this compressed granular system is transversely isotropic; (8) the contact forces are directed more vertically with depth, making the macro lateral pressure ratio decrease with depth.