Footprints: the Role of Particle Characteristics

Soils are particulate materials. Grain size determines the balance between particle-level forces (skeletal, weight, van der Walls attraction, double layer repulsion, capillary and viscous drag Figure 1). Grain size distribution establishes the range of possible particle packing configurations. And, particle shape (i.e., sphericity, angularity and roughness) defines particle interactions, such as slippage vs. rotation, and the development of both inherent and stress-induced anisotropy (see Figure 2). Therefore, macro-scale behavior is determined by particle-level characteristics. In particular, extreme void ratios emax and emin and critical state soil parameters ( Γ and e cs φ cs) can be estimated from roundness R, sphericity S ( for Cu ≤2.5 Cho et al., 2004):