The multiscale structure of granular matter and its mechanics

Soil is the naturally occurring, unconsolidated or loose covering of broken rock particles, which consists of densely packed solid particles, interstitial liquid and gas. This collection of particles forms a supporting skeleton and determines the ability of soil to resist shear stress, as described in the concept of effective stress proposed by Karl Terzaghi. Many efforts have been made to apply this concept in engineering problems, rather than conducting more fundamental investigations on the geometrical and mechanical properties of the soil skeleton. In the past two decades, the closely related discipline of granular matter mechanics has received much attention due to its various intriguing phenomena. Many fundamental studies have provided a deeper understanding of granular matter. Based on our research on soil mechanics and granular matter in the last ten years, we propose that soil is intrinsically multiscale, i.e. besides microscale primary particles and macroscale bulk matter it also consists of mesoscale force chains. The correlations among the different scales are crucial. The mesoscale force chain network is determined both by particle properties and macroscopic boundary conditions. The evolution of the force chain network contributes to the macroscopic mechanical properties of soil.