Prediction of the Trafficability of the Tractor on the Soft Paddy Field (VI)

Drawbar Pull and Soil Parameters

Abstract

The problems of the tractor sinkage on the soft soil are a matter of the floatation under the vertical direction.
The performances of the tractor are not only disclosed by the floatation, but traction of them are more important factor.
If the traction or drawbar pull on the various soil condtions will be able to predict easily as same sa the prediction of the sinkage by a cone or the other methods, we could know the tractor concept or mechanism to improve the traction, but this problem contains many difficult factors as revealed in many research papers.
This test and analysis were aimed to find out the starting points to predict the traction by the tractor elements and soil conditions.
Three soil conditions having the various internal friction angle and cohesion force shown in figure 1 were selected and five tractors which equipped pneumatic tire, half tracks, girdles and double tires were used.
Tractor sinkage was proportional with the slippage of the running elements and contact surface increased with the sinkage and contact pressure decreased. Curves of traction on a unit ground contact surface area vs. contact pressure were shown in figure 4 and this curves did not cross the lines of the shearing resistances of soil which the tractor tested.
Curves of traction on a unit ground contact surface area vs. slippage (deformation of soil) were quite similar with the curves of stress-strain curves at the soil shearing test.
This clarified the soil under the running elements were sheared by them and the traction was the resultants of shear resistance of soil.
Maximum drawbar pull on a unit contact area was proportional with maximum resistance of shearing soil as in figure 6 and had the linear relation with the contact pressure as in figure 7.