Models of soil compaction due to traffic and their evaluation

Soil compaction by wheeling may cause considerable damage to the structure of the tilled soil and the subsoil and consequently to crop production, workability and the environment. Soil compaction models are reviewed and their evaluation under laboratory or field conditions is discussed. The development of a compaction model includes: (i) modelling the propagation of the loading forces within the soil resulting from forces applied at the soil surface from farm vehicles; (ii) modelling soil stress–strain behaviour. Models predict stress distribution in the soil induced by farm vehicle and change in soil structure: increase in dry bulk density and rut depth formation. We conclude that models based on Boussinesq equations for stress propagation are useful since they use a small number of parameters. They have been successfully evaluated in field conditions for homogeneous soil under a wide range of soil and water conditions. The difference between simulations and observations becomes more apparent when dealing with heterogeneous structures (clods, firm subsoil). The models based on the finite element method (FEM) have been shown to be more adequate for modelling the 3D distribution of stress within the soil induced by wheeling and the complex stress–strain behaviour of soil. Nevertheless, these models require more mechanical parameters and have been evaluated under limited conditions in laboratory bins or in the field with low compaction intensities. This review stresses the need to test FEM soil compaction models, so as to extend the range of conditions where these models can be applied.