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A discrete element model and its experimental validation for the prediction of draft forces in cohesive soil

Martin Obermayr, Christos Vrettos, Peter Eberhard, Thomas Däuwel
Journal of Terramechanics, Volume 53, June 2014, Pages 93-104, ISSN 0022-4898,
Abstract: Soil can roughly be classified into cohesionless, cohesive, and cemented soil. In this contribution, a discrete element model for the simulation of cohesive soil is presented. It is based on a model for cohesionless material with spherical particles, normal repulsive and frictional contacts, as well as rolling resistance with an elastic limit to compensate the excessive particle rolling. The cohesive behavior is modeled by an additional attractive normal force between particles. The model is not derived from one of the microscopic origins of cohesion, such as liquid bridges or electrostatic forces. Instead, it is set up in analogy to the macroscopic shear failure characteristics of cohesive soil. The model is stress history dependent. By that, the amount of cohesion is limited by the pressure that contacting particles have experienced during the course of the simulation. The discrete element model is shown to be scale invariant in the quasi-static regime, i.e. if all lengths of the model are scaled, the results remain unaffected by the scaling. The model is applied to a small-scale laboratory test and an excavator digging in natural cohesive soil. The contact parameters are calibrated by simulated triaxial compression tests. A comparison between simulation and measurement shows good qualitative and quantitative agreement.
Keywords: Discrete element method; Cohesive soil; Reaction force; Soil-tool interaction