Cranfield University

Appendix
by Seig (1985) who showed a benefit for a long narrow contact patch compared to a short
wide one. The same benefit was shown in this study as detailed in Section 7.2. However, for
simplicity the turning approach was chosen.
Table 3: Initial DBD and moisture content values in O’Sullivan model and resulting
�
[g/cm 3 ]
Water
content
[%]
parameters
Average
increase in �
for tracks [%]
Average increase
in � for wheels
[%]
Rut depth
track [mm]
Rut depth
wheels
Ph.D. Thesis Dirk Ansorge (2007)
[mm]
1.37 10 2.9 3.9 15 20 325
1.27 10 10.3 11.4 52 58 325
1.20 10 17.2 18.4 86 93 375
1.15 10 22.3 23.3 112 117 275
1.2 15 19.5 20.7 98 104 425
1.36 15 4.5 5.6 23 28 325
1.36 20 12.8 13.5 64 68 125
Minimal Depth of
similar compaction
When mimicking tracks, soil compaction is slightly reduced compared to that of tyres, yet on
average only by 1 % compared to 5 % during the experiment.
The next three paragraphs discuss the predicted results for varying initial dry bulk density
shown previously in Table 3.
Comparison of prediction behaviour of COMPSOIL for a range of soil densities and moisture
contents
Initial dry bulk density of 1.27 g/cm 3
At an initial soil density of 1.27 g/cm 3 the difference in average increase in DBD between the
“track” and the tyres is still merely 1.1 % although the total increase in soil density has
increased to 10.3 % for the track and 11.4 % for the tyre. Again, as already discussed by
Ansorge (2005), the increase caused by the tyre at half inflation pressure is bigger than the
one caused by the 900 mm section tyre. The resulting displacement is not consistently
decreasing with depth. Decrease is higher close to the surface and less at depth. Total
displacement at the surface increased from about 15 – 20 mm to about 52 – 55 mm. Similar to
the model run with the true soil conditions, the last 4 layers have the same displacement
independent of the treatment. This can not be supported with the findings by Ansorge (2005).
[mm]
198