Cranfield University

Appendix
Table 8: n and k depending on initial DBD
Soil Density n k
Soft 1.2 g/cm 3
Medium 1.4 g/cm 3
Dense 1.6 g/cm 3
11.1.7.3.1 Sinkage of Tyres
0.89 700
0.62 2150
0.42 2400
The values from Table 8 were used in Eq. 6 to calculate the sinkage of the rear tyres only on
medium soil condition; however the front tyres were calculated on all three soil conditions.
The sinkage data for the soft and dense soil condition is from Antille (2006) and the medium
condition from Ansorge (2005). The tracks have not been included at this stage. As breadth of
the tyre once the width of the tyre was used and in a second step (as suggested by Bekker,
1960) half the length of the foot print as this was always shorter than the width of the tyre.
The estimated rut depth is plotted against the measured rut depth in Figure 46.
Predicted Depth (mm)
500
450
400
350
300
250
200
150
100
50
0
0 100 200 300 400 500
Measured Depth (mm)
Real Contact Width
1:1 Line
Half Contact Length
Triaxial Fast Real Width
Triaxia Fast, Half Length
Linear (1:1 Line)
Figure 46: Predicted vs. Measured depth of the tyres from plate sinkage data
The predicted and measured rut depths for the dense and medium soil condition show
tolerable deviation, whereby using the tyre width for the shortest contact length results in a
slightly underpredicted sinkage compared to using half the contact length which results in a
slightly overpredicted rut depth. However, on soft soil conditions, the deviation is about 100
%. This might be due to the fact that the Bekker model assumes an infinite soil depth below,
whereas in the soil bin, the maximum depth is 750 mm. On medium soil conditions, the
results could be replicated using the plate sinkage data gained from tests in the triaxial test as
described in Section 2.8. This shows that plate sinkage tests can be used for both the
Ph.D. Thesis Dirk Ansorge (2007)
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