Cranfield University

Appendix
the evaluation of the behaviour of the model with respect to the slope of the recompression
line (RCL) which determines soil behaviour at the beginning of reloading (the second cycle in
a loading-unloading sequence). The smaller the slope of the RCL the faster soil compacts in
the consecutive loading cycles and has undergone less strengthening than one with a larger
RCL slope.
As the close agreement between measured and predicted data shows, the model predicts the
soil behaviour correctly for subsequent passes without the necessity to adjust the RCL. The
slope of the RCL = 0.0327 as defined by O’Sullivan (1998) can be maintained for this sandy
loam, too. In general a close agreement at the surface is achieved and only displacement
behaviour at depth differs slightly when the displacement approaches zero anyway and the
deviation is still within the error of measurement.
Depth (mm)
0
100
200
300
400
500
600
700
800
Deformation (mm)
-20 0 20 40 60 80 100 120 140
10.5 t Multipass Measured
10.5 t Multipass Predicted
5 t Multipass Measured
5 t Multipass Predicted
Figure 14: Predicted and measured soil displacement after multipasses of a 900 mm tyre
11.1.3.4 Passes with complete vehicles
Figure 15 shows the predicted soil displacement below vehicles after the pass of the front and
the rear axle. In general a close agreement was obtained between measured and predicted soil
displacement. A close agreement was found for both the 900/10.5/1.9 followed by the 500-
70/4.5/2.3 (900-500) and the 590/4/1.2 followed by the 290/1.5/2 (590-290). For the
900/10.5/1.9 followed by the 700/10.5/1.0 (900-700) combination rut depth prediction was
significantly smaller than the measured value, but the slope was similar. The 680/10.5/2.2
followed by the 500-85/4.5/1.4 (680-585) had closer agreement with respect to the predicted
rut depth, but overall the slope differed more.
Ph.D. Thesis Dirk Ansorge (2007)
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