Contact force network evolution in active earth pressure state of granular materials: photo-elastic tests and DEM
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ORIGINAL PAPER
Contact force network evolution in active earth pressure state of granular materials: photo‑elastic tests and DEM D. Leśniewska1 · M. Nitka2 · J. Tejchman2 · M. Pietrzak3 Received: 21 September 2019 © The Author(s) 2020
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. Keywords Granular material · Photo-elasticity · Discrete element method · Digital image processing · Force network localization · Redundancy factor · Experimental testing
1 Introduction The active state of granular material is one of the basic concepts of classical soil mechanics, derived from historical observations of retaining structures at failure. The first earth pressure calculus is attributed to the fundamental paper by Coulomb [1], where the concept of a soil wedge moving along a slip line, out of the soil mass, is formulated. This was the first description of the retaining wall failure mechanism and at the same time the first definition of soil (granular material) active state. Numerous experiments on small scale models of retaining walls using radiographic technique convince that the state of the active earth pressure usually produces simple localization patterns, consisting of well-defined shear bands [2–12]. Such patterns make models of retaining walls attractive
* D. Leśniewska [email protected] 1
Institute of Hydro-Engineering PAS, 80‑328 Gdańsk, Poland
2
Gdańsk University of Technology, 80‑233 Gdańsk, Poland
3
Koszalin University of Technology, 75‑453 Koszalin, Poland
for testing shear bands in more complex and less uniform boundary conditions than those offered by element tests. Following this research line, Leśniewska and Muir Wood [13] and Muir Wood and Leśniewska [14] applied the active retaining wall scheme to study both deformation and force networks, using surrogate grains (glass beads). Niedostatkiewicz et al. [12] investigated the experimental patterns of shear bands for both active and passive earth pressure conditions using digital image correlation (
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