Compaction of soil caused by increasing mechanical loads and repeated wheeling may result in reduced soil productivity. The physical response of soils to such loading is analysed with a non-linear finite element program using incremental tangential moduli with incremental loading and unloading from known initial conditions. During each load increment an iterative procedure is used to determine more accurately the stresses and the stress dependent moduli. This program is designed to model the linear elastic and plastic behaviour of soils with stress and moisture dependent properties with strain softening and irreversible load responses. The relevant material parameters are discussed and suggested methods of measuring them in standard soil mechanics test procedures are proposed. The use of such models in predicting soil behaviour must always involve a balanced integration of the measurement of the material parameters and boundary conditions for the problem, the use of appropriate analytical techniques and field verification. Practical examples are given to show how this has been done in interpreting field experiments and to confirm that the techniques can predict the physical response of soil profiles to repeated wheeling.