The relationship between precompression stress and rut depth of different soil types in Estonia
¹Dept. of Soil Science and Agrochemistry, Institute of Agricultural and Environmental
Sciences, Estonian University of Soil Sciences, Kreutzwaldi 1a, EE 51014 Tartu, Estonia
²The Estonian National Defence College, Riia 12, EE 51013 Tartu, Estonia
In agriculture as well for other purposes off-road vehicles have to move cross-country. Precompression stress is used to describe the load bearing capacity of different soils. The aim of the study is to investigate the relationship between precompression stress and rut depth for different Estonian soil types after 1 and 10 passes of a vehicle. Traffic experiments were conducted at eight experiment sites throughout Estonia using a 7 t truck and a 23 t wheeled vehicle. The experiment sites were selected based on the Estonian soil map. Rut depth was measured after the first pass and ten passes. Undisturbed soil samples were collected from topsoil and from subsoil right next to the track. Soil samples were compressed in an oedometer at stresses of 25, 50, 100, 200, 400 and 600 kPa. The Casagrande procedure was used to determine the precompression stresses. In topsoil, if the moisture content of a soil is high, then the differences in the precompression stress values of the various soil types disappears while in the subsoil layer the precompression stress is more dependent on the soil properties. The precompression stress cannot by itself be used as a threshold value to determine small and large sinkage. The choice of fitting methods for composing of stress compaction curve is critical and led to the preference of the logistic curve. The values of logistic functions at the points of their maximal curvature and calculation based on the area on stress-compaction graph can be used for prediction of rut depths.