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Simulation of plowing and cutting processes in soils is challenging and time-consuming due to large deformations and contact interactions. Recent studies on sand have suggested that a simplified, efficient approach based on incremental plastic analysis can capture the essential physics and features of the problem. The present study refines this technique by enhancing the kinematics and implementing a more sophisticated material law. The effects of hardening and softening, as well as dilatancy and compaction, are introduced. With the modified model, it is observed in the case of hardening (compaction) that the occurrence of multiple successive shear bands at variable locations gives the appearance of continuous shearing in the final pattern of deformation. This is markedly different from the previously predicted response in the case of softening (dilatancy), where shear bands appear at distinct locations and transition from one discrete location to the next. The computed results are compared with preliminary experimental data gathered in the Soil-Structure and Soil-Machine Interaction Laboratory (SSI-SMI Laboratory) at Northwestern University. 

Accurate estimation of soil mechanical properties represents a crucial step for most engineering applications. Both in situ and laboratory testing fundamentally rest on mechanically deforming (actuating) the material and simultaneously measuring its response in terms of displacements and stresses (reactions). Facing this widely adopted scheme, key questions remain unanswered: 1) what is the optimal type and/or mode of actuation that can most effectively extract soil properties; 2) what types of measurements are most useful for inferring material constants? As a first step in the investigation of these questions, an inverse model for the direct simple shear (DSS) test is constructed, wherein measurable responses are used to back-calculate soil properties. Specimens with two different aspect ratios are considered to study the influence of the deformation mode. The effect of the choice of measurements (i.e., which displacements and/or stresses are observed) is explored by assessing inverse model performance considering the DSS test as a boundary value problem, with variable displacement and stress fields, versus the conventional interpretation as an elemental test. Parameter sensitivities and correlation coefficients are employed as quantifiable metrics to compare material characterization based on different aspect ratios and types of measurements, and to interpret the performance of inverse analysis.