Distribution uniformity of soil stress under compaction of tracked undercarriage

Abstract: Tracked undercarriage is considered as a technical solution to reduce the soil compaction as compared to the tire due to its large contact area between track and soil. However, the interaction between track and soil is complex, resulting in uneven distributed stress at track/soil interface. Uneven distributed stress may reduce the ability that track decreases the soil compaction and will also lead to the increases of track sinkage depth, which may reduce the vehicle's traffic-ability. Therefore, we can better understanding of the soil compaction process with the help of investigating the distribution of soil stress beneath the tracked undercarriage. The objectives of this study were to estimate the distribution of soil vertical and horizontal stresses under the tracked undercarriage in the track length direction, and to investigate the effect of track tensions on the distribution of soil stress. The test was conducted on the sandy loam soil and combine harvester equipped with rubber tracks was used in the test. The rubber tracked undercarriage system is comprised of a front wheel and a rear wheel with two support wheels. During measurement, the harvester was unloaded and without its header. The soil stress was measured by embedding the pressure sensors under the centerline of the track at depth of 0.35m. In total four pressure sensors were installed: two sensors for vertical stress, and two sensors for horizontal stress (piston facing the vehicle's driving direction). A laser position sensor fixed on the ground was employed to track the positions of the axle of track wheels. Three repeated measurements were performed with different track tensions (i.e. 1.6×104, 1.7×104, and 1.8×104 kPa) at same traffic speed. The results showed that the measured vertical stress presented three peak points along the track length, with two peaks beneath each axle of track drive wheel and guide wheel, and one peak between two support wheels. The horizontal stress presented two peaks before and after each wheel axle, with the minimum stress on the axle. Moreover, the magnitude of soil stress beneath each of track wheel were different, with the largest vertical stress beneath the guide wheel, and the largest horizontal stress between guide wheel and rear support wheel. The maximum stress and mean maximum stress under the track were decreased with the decreasing of track tension, when the track tension was reduced from 1.8 × 104 kPa to 1.6 × 104 kPa, the maximum vertical and horizontal stresses were reduced by 37.3% and 21.7% respectively, and the mean maximum vertical and horizontal stresses were reduced by 26.4% and 20.4% respectively, which indicated that decreasing the track tension could improve the uniformity of the soil stress. However, too small track tension will lead to relaxation of track, resulting in track failure and affecting the ride comfort of the vehicle. Therefore, it has limitations in improving the uniformity of stress by reducing track tension. Some other methods, such as optimizing the configuration of track wheels along the track length, may also improve the uniformity of the soil stress under the tracked undercarriage. More investigation about the effect of track wheel configuration on the soil stress distribution is needed in the future work. This study can provide preliminary guidance on optimizing the structure of tracked undercarriage to improve the uniformity of soil stress.