SOCOMO: a soil compaction model to calculate soil stresses and the subsoil carrying capacity

Intensification of crop rotation and increasing use of machinery with high wheel loads are clearly related to compaction of the subsoil. Subsoil compaction is persistent and the effect of natural and artificial loosening has been disappointing. Therefore, prevention of subsoil compaction is the best way to preserve the structure and quality of the subsoil. In addition to field studies, there is an increasing need for analytical tools to develop and evaluate measures for preventing subsoil compaction. The objective of the research was to develop such a tool in the form of a computer model suitable for educators and extension workers, professional advisers, agricultural engineers and scientists. The analytical soil compaction model (SOCOMO) was developed to calculate soil stresses under wheel loads. In specific cases, the calculated stresses are compared with soil strengths measured in the laboratory. The calculated stresses were compared with known soil strengths or soil strengths determined with the help of pedotransfer functions. Subsoil compaction and deformation are prevented if the stresses exerted remain smaller than the actual strength of the subsoil. To test the model, traffic experiments were performed and methods developed to measure stress, compaction and deformation in the subsoil caused by wheel load. The test was successful and the model has been used to compare stresses under normal and low-pressure tires, as well as under tandem and dual-wheel configurations. SOCOMO was also used to construct a wheel-load carrying-capacity map of The Netherlands. The model is easy to use and requires only minimal input. However, it is not yet as user-friendly as it could be. Weak points of the model are that the rut depth must be estimated and that the shape of the pressure distribution exerted by the tire on the bottom of the rut is based on rules of thumb. The use of the concept that subsoil compaction can be prevented by keeping the exerted stresses on the subsoil below actual strength is frustrated by the fact that data and pedotransfer functions of soil strength are scarce. More measurements and development of pedotransfer functions are required.