Predicting soil response to a driven pneumatic wheel using finite element analysis

A three-dimensional finite element (FE) procedure was described for elasto-plastic analysis of the stress-strain distribution within unsaturated soil. This model can predict the deformation of unsaturated soil in response to applied stresses. The development and evaluation of the non-linear finite element procedure presented herein includes: (1) An elasto-plastic constitutive relationship based on the modified Cam Clay model; (2) Model input parameters determined by conducting a series of unsaturated triaxial soil tests; (3) Using the FE model to simulate triaxial testing for both saturated and unsaturated soil conditions; (4) Measurement of three-dimensional soil deformation for tractive wheel loading in a soil bin; and (5) Simulation of tractive wheel loading and comparison of predicted and measured deformation.; The non-linear three-dimensional finite element model (FEM) that incorporates matric stress developed in this study agrees well with published models of saturated soil stress-strain behavior, and suggests a simplified procedure for describing stress-strain behavior for unsaturated soil worthy of development. A modified triaxial testing procedure is described to obtain soil property parameters, especially parameters for unsaturated soil. A laboratory procedure was developed to measure three-dimensional soil deformation with a soil bin and sonic digitizer system. Soil deformation predicted for the operation of a powered pneumatic wheel agreed well with deformation measured vertically and laterally. Inaccurate measurement of deformation along the direction of wheel travel made evaluation of predictions in the third dimension impossible.; Results of this study indicate that FE modeling is an efficient approach in the study of the mechanics of unsaturated soil. The developed FE model is therefore quite applicable in predicting deformation in agricultural soils.