Prediction of draft forces in cohesionless soil with the Discrete Element Method

The Discrete Element Method (DEM) is applied to predict draft forces of a simple implement in cohesionless granular material. Results are compared with small-scale laboratory tests in which the horizontal force is measured at a straight blade. This study is focused on the case of cohesionless material under quasi-static conditions.The DEM requires the calibration of the local contact parameters between particles to adjust the bulk material properties. The most important bulk property is the angle of internal friction ϕ. In the DEM, the shear resistance is limited in the case of spherical particles due to excessive particle rotations. This is cured by retaining rotations of the particles. Although this is known to prevent the material from developing shear bands, the model still turns out to be capable of predicting the reaction force on the blade.In contrast to empirical formulas for this kind of application, the DEM model can easily be extended to more complex tool geometries and trajectories. This study helps to find a simple and numerically efficient setup for the numerical model, capable of predicting draft forces correctly and so allowing for large-scale industrial simulations.

Numerical Simulation of Draft Forces with DEM.Figure optionsDownload as PowerPoint slideHighlights
► Soil–tool interaction is modeled with DEM for a straight blade at constant speed.
► Rotational degrees of freedom of particles are retained for larger shear strength.
► Calibration is achieved by simulated triaxial compression tests.
► Guidelines for the selection of model parameters and the calibration procedure are given.
► Results show good agreement with small-scale laboratory tests.