FEM based soil stress and strain analyses aimed at plant growth factors

<p>During vehicular traffic on agricultural soils, the soil is subjected to a loading process which finally results into a change of micro-factors, such as the amount and distribution of water, solid parts or bounds, not arising from the soil water, between these solid parts in the soil. Derivations of the micro-factors are the so-called soil qualities like coefficient of oxygen diffusion and water permeability, moisture characteristic, root penetration resistance and the coefficient of heat conductivity. Seeds and plants need a specific set of values of these soil qualities to grow properly.</p><p>The loading process of the soil is simulated through an impression of a strip into the soil with the help of a finite element method. Description is given of stress and strain theories with respect to a cubical soil body, the elastic-perfectly-plastic Mohr-Coulomb model, the soil-material interface and finite and interface elements of the used finite element program Plaxis. Derivation of soil model parameters for the finite element program Plaxis is given in case of a presented reference soil, a wet moderately heavy river clay with an entrapped air percentage of 5%. Beside soil model parameters of the Mohr-Coulomb model, attention is given to soil model parameters of the elastic region of the Plaxis-Cap model.</p><p>A reference soil-load system is presented with corresponding finite element input. For handling the large amount of finite element output results, the stress and strain analysis program Trestana is developed. Characteristic of the program is that three-dimensional plots of quantities can be presented against the deformed mesh as ground surface, without loosing information through the use of smoothing procedures.</p><p>Finally, single and composite quantities are presented which can serve as building blocks for constructing so-called kneading numbers of soil. This all in view of the idea that changes of kneading numbers correlate reasonably with the changes of the soil qualities.</p&gt