Contact force network evolution in active earth pressure state of granular materials: photo-elastic tests and DEM

Abstract

The paper deals with a quasi-static behaviour of cohesion-less granular material in active earth pressure state. Photo-elastic model tests on a rigid wall, translating out of the granular material, are analyzed. Grain crushing tests are used to estimate the range of contact forces during the model tests. Substitute granular material (low optical sensitivity glass granules) is employed. The focus is on the evolution of contact force network with deformation of granular material. The model tests are simulated using the discrete element method (DEM) to compare physical and numerical full-field force network structure and the maximum/minimum stress level. The same model geometry, loading scheme and grain size distribution, as in the model tests, are accepted in DEM simulations, although only a single layer of grains is modelled. DEM model correctly predicts the overall structure of the force network and its characteristic features, including localization. It also gives the stress level close to the experimental one and properly identifies the areas of phase transitions.

Bursting Sand Balloons

“…Measurements show that spatially extended and strong force chains (much larger than the mean force) occur when the applied stresses are large (although these are exponentially rare [29]); conversely, short and weak force chains are produced for small stresses [25,27]. Moreover, the force-force spatial distribution function and contact point radial distribution function indicate that the spatial correlations between the contact forces and positions of the contacts extend out only to approximately three particle diameters.…”

“…A last issue concerning the inner structure of the granular mass is related to the possible existence of force chains, which are typical in granular masses subjected to strong compression stresses [25][26][27][28][29][30]. Chain forces in two-dimensional granular materials have been found experimentally through photoelasticity [25][26][27], force sensors [28], and the use of DEM and lattice Boltzmann simulations [25,27].…”

Force chains in crystalline and frustrated packing visualized by stress-birefringent spheres

“…Such experimental studies, however, are essentially restricted to 2D systems, with few exceptions. [44][45][46] Our stressbirefringent spheres in a flat cell may be considered as an extension of the previous work with disks. There are several quantitatively different and new aspects when one uses spheres: First, the optical analysis requires an immersion fluid, otherwise the polarization by refraction at the sphere surfaces would obscure the stress-induced birefringence.…”