Effects of repeated rolling of agricultural tractors on soil stress and deformation state in sand and loess

The stress and deformation state was determined in sandy and loess soils under loading by agricultural tractors, driven at a velocity of 5 km/h several times in the same track. The soil stress state was determined with the use of a stress state transducer, which was installed at two depths: 15 and 30 cm. Soil deformations were determined with an optical system, which enabled the determination of deformations of a 30 cm ×30 cm square, in the direction of travel. It was determined that an increasing number of rolling events influenced both soil stress and deformation state. Stress state components continuously increased, but the most intensive increase was observed during the two first passes. Similarly, soil deformations saw the greatest increase in the first two succeeding wheel passes, and then more slowly. There were observed differences between the reactions of sandy and loess soils: the increase of soil stress, as well as the peak maximum stress values, were higher for sandy soil. A difference in soil deformation state for the two investigated soils was also observed. In the case of loess soil, significant shearing occurred, while for the sandy soil, a more intensive volumetric deformation was observed with less shearing.