Soil reaction to heavily loaded rubber tracks and tyres

摘要

The importance of undercarriage design with respect to its effect on soil density changesgrows with the size of harvest machinery. Therefore this study elucidates the mechanics ofsoil displacement caused by different undercarriage systems of combine harvesters on soil.The soil displacement caused by different undercarriage systems at maximum workingweight was measured by embedding tracers into the soil in both the soil bin laboratory andthe field studies. The effects of different tyres, tracks, and whole undercarriage systems onsoil density increase were significant. The results from whole machine systems were validatedwith field experiments using fish-hooks for measuring displacement on a sandy loamand a clay soil. The draught force of a tine loosening the soil after the passage of wholemachines was also investigated.With an increase in speed, soil density increase was reduced. The implement tyre evaluationemphasized the importance of tyre width, diameter, and inflation pressure on soil densityincrease. The evaluation of whole machine systems showed that the influence of reartyre size on additional soil density increase is larger for wheeled than for tracked undercarriagesystems. The strong layer at the surface from a track is able to carry the rear tyrewithout further compaction of the soil below leading to an overall soil displacement similarto a wheeled machine of 1/3 of the weight. The evaluation of different track systems emphasizedthe effect of the number of rollers on soil physical parameters. Variations in ahigh belt tension range showed only small effects.A novel approach was developed determining virgin compression line parameters in-situfrom contact pressure, rut and working depth enabling an easy adjustment of a model togiven soil conditions and a successful prediction of soil displacement for tyres. The in-situapproach can be used for tracks, but a different VCL results. The in-situ VCL was validatedwith small scale plate sinkage tests and compared to results from triaxial cell testing.Results from triaxial tests showed that the VCL depends on the relation of major and minorprincipel stresses. Ancillary experiments were carried out to shed light on longitudinal soilmovement and the influence of lugs and pressure history on soil displacement. In additiona new heuristic model involving load per perimeter length was tested and the “punchingfailure” of soil observed justified with theories from literature. Ancillary experiments showed that the dense layer at the surface from the tracks originatesfrom a backward soil movement limited to the uppermost 150 mm. The lug influence ofboth tyres and tracks was insignificant from 200 mm depth downwards. From heuristicaldata analysis the load per perimeter length was identified as an important variable. Peakedpressure history caused about 1/3 more sinkage than constant contact pressures.