The effects of tyre size on soil deformation and soil bulk density changes

The selection of appropriate tyre size and inflation pressure for a particular load and soil condition are crucial to minimising soil compaction and ensuring soil sustainability. The purpose of this study was to investigate the changes in soil bulk density from soil deformation data, produced by a selected range of combine-harvester tyres, inflated to the recommended inflation pressures, and at high axle load (10.5 tonnes) to provide a valuable indicator for tyre selection. Results showed that the initial soil strength was the main factor influencing soil deformation and soil bulk density changes beneath the tyres. In addition, increased tyre size and low inflation pressure reduced both soil deformation and the resultant increase in soil bulk density. The increases in soil bulk density after one passage of the tyres over the soil were approximately 25% for the low bulk density soil (1.20 g cm-3) and between 2.3% and 5% for the high bulk density soil (1.60 g cm-3). The advantage of increasing tyre size and lowering inflation pressure was also reflected in the results obtained from penetrometer resistance: at the centre of the wheeling, the tyre with the highest inflation pressure (2.5 bar) gave a significantly higher increase in penetration resistance compared with the tyres with lower inflation pressures (2.2 bar and 1.9 bar). Linear relationships between drop-cone penetration and maximum rut depth were established; these data were subsequently related to those obtained from penetration resistance and initial soil bulk density; therefore, the increase in soil bulk density induced after driving a tyre over the soil can be determined for various tyre configurations and initial soil conditions.