Determination of discrete element model parameters using in-situ tests and inverse solution techniques

The dynamic interaction between soil and tools includes a high rate of plastic deformation and soil failure, characterized by flow of the soil particles. The discrete element method (DEM) seems to be a promising approach for constructing a high-fidelity model to describe the soil-tool interaction. Proper prediction of this interaction using DEM depends upon the model parameters. However, there is no robust method for determining the parameters for discrete element models. In this study, the determination of parameters was based on in-situ field tests, which consist of sinkage tests performed with different penetration tools. Based on each test, a plot of force versus displacement, or a so-called "real curve," was drawn. Discrete element models were built in correspondence with the field tests. "Simulation curve" plots were obtained from the results of the simulation of force versus displacement. In order to minimize the area difference between the real and simulation curves, an inverse solution technique using the Nelder-Mead algorithm of optimization was employed. The optimization results of this particular problem are sensitive to the initial estimate of the parameters. In order to achieve a unique solution, the initial estimate must be close enough to the proper value of the parameters. An energy method and elastic plastic rule were developed to determine the initial estimation for the optimization process. The described methodology was verified numerically with very good soil model parameter estimation.