Modeling soil aggregate fracture using the discrete element method

The Discrete Element Method (DEM) is a suitable approach for modeling and simulating arable soil and tillage processes. In this work, we focus on modeling soil fragmentation which is a vital element of many soil treatments. We present a method for computing the indirect tensile strength of soil aggregates through simulation. DEM aggregates are constructed as spherical clusters of smaller spherical particles. A number of indirect tensile tests are conducted using simulated aggregates from which the critical polar force and tensile strength are identified. We propose a method for introducing random voids such that the distribution of simulated tensile strength corresponds to a given Weibull distribution. We propose to scale the number of voids linearly with the measured porosity of the aggregates. This approach showed better performance than introducing a constant number of voids. We identified that the friction between the sub-spheres can be related to the characteristic strength and the number of voids is related to the spread of strengths in the Weibull distribution. The calibration and validation are performed on experimental data. Based on this approach, the synthetic DEM aggregates allow for deriving the aggregate strength as a function of aggregate size. The results are based on fracturing individual aggregates but can be extended to simulations involving multiple interacting aggregates.