Cranfield University

Appendix
by O’Sullivan et al. (1998) is given in Figure 5. This shows a very large deviation for both
uniform and stratified soil. This suggests that either the soil specific parameters used to
describe the sandy loam soil of the model do not adequately describe the sandy loam soil used
in the soil bin or there are substantial errors in the model. The latter is unlikely as O’Sullivan
et al. (1998) showed close agreement for other soil types. Consequently the VCL parameters
for the sandy loam of the Cottenham Series (which was used by Ansorge (2005) and this
study) have to be different from the sandy loam soil described by O’Sullivan et al. (1998) and
used by the original COMPSOIL model and hence need to be determined.
Depth (mm)
0
100
200
300
400
500
600
700
800
Deform ation (m m)
-20 0 20 40 60 80 100
Figure 5: Measured (solid line) and predicted (broken line) soil displacement for
900mm section width tyre at 10.5t load and 1.9bar inflation pressure on
uniform (□) and stratified (×) soil conditions (measured data from Ansorge
(2005))
The VCL as defined by Schofield and Wroth (1968) is a unique linear function relating the
relative density of a soil at given moisture content to the natural logarithm of the spherical
pressure it is subjected to. According to their definition spherical pressure is the arithmetical
average of major, intermediate, and minor principle stress, � 1,
� 2 , and � 3 , respectively. As
mathematically this is the definition of the mean normal pressure p, this paper will use the
term mean normal pressure after O’Sullivan et al. (1998) when developing the COMPSOIL
model.
The VCL is usually obtained from plotting the relative density (ratio of the maximum soil
density (2.66 g/cm 3 ) to the resulting dry bulk density) against mean normal pressure measured
with triaxial cell tests. For the assessment of the in-situ VCL in the soil bin the relative
Ph.D. Thesis Dirk Ansorge (2007)
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