Feasibility of Using PFC3D to Simulate Soil Flow Resulting from a Simple Soil-Engaging Tool

Abstract

<abstract> <b><sc>Abstract.</sc></b> PFC^3D is a discrete element modeling tool that has been used for simulations of soil-tool interaction in agriculture. However, existing studies have mainly focused on simulations of soil cutting forces, not soil flow. In this study, a soil-tool model was developed using the parallel bond model (PBM) of PFC^3D to determine if the model could be used to simulate the soil flow characteristics resulting from a simple soil-engaging tool while satisfying the draft force prediction accuracy. In the simulations, soil was modeled as spherical particles with bonds between particles. The model outputs examined were the two most important soil dynamic properties: thrown-soil and draft force. By examining the effects of model microproperties on the simulated thrown-soil and draft force, we found that the feasible ranges of the model microproperties were: 1e4 to 5e6 Pa for the modulus of elasticity of particle, 1e5 to 1e8 Pa for the modulus of elasticity of bond, 1e4 to 1e5 Pa for bond strength, 0.3 to 0.7 for local damping coefficient, and 0 to 1.0 for viscous damping coefficient. For simulation of soil-tool interactions, the model microproperties should be selected within these feasible ranges. Otherwise, the behavior of the model particles would not reflect the behavior of real soil. Within these feasible ranges, the model outputs were influenced the most by the modulus of particle elasticity; the other model microproperties had little impact on the model outputs. Soil cutting tests were conducted in a sandy loam soil to evaluate the soil-tool model. The results showed that a modulus of particle elasticity of 2.5e5 Pa resulted in a good match between the simulated and measured draft forces. However, with this modulus, the simulated thrown-soil was significantly lower than the measured value. Further investigations showed that it may not be possible to match the simulated and measured thrown-soil using the PBM of PFC^3D. Therefore, redefining the constitutive laws of particle contacts would be required to improve the accuracy of the model for simulations of soil flow behavior.