Cranfield University

Soil Compaction Models
and 13.7 % by assuming that the top 600 mm of soil uniformly increased in DBD. Initial
DBD was 1.27 g/cm 3 and resulted in relative densities of 1.911 and 1.843 when adding the
increase in DBD for the low and high inflation pressure, respectively. Contact pressure was
estimated according to O’Sullivan et al. (1998), and resulted in a mean normal pressure of
52.9 kPa and 55.9 kPa for the low and high inflation pressure, respectively at � of 5 fol-
lowing the calculations given in detail in Section 6.3.2. At � of 4 the corresponding pres-
sures were 57.5 kPa and 60.8 kPa. In Figure 79 the relative density is plotted vs. mean
normal pressure for both concentration factors and a logarithmic regression line is fitted to
each set of data resulting in the corresponding in-situ VCLs for the clay soil.
Rel. Density
3
2,5
2
1,5
1
0,5
0
y = -0,1961Ln(x) + 2,6604
R 2 = 0,996
y = -0,1921Ln(x) + 2,6604
R 2 VCL Clay Conc=5
VCL Clay Conc=4
= 0,9959
Logarithmisch (VCL Clay
1 10 100
Pressure (kPa)
Figure 79: VCL for cay soil gained in field experiment
If the slope of -0.1961 and the intercept of 2.6604 corresponding to a � of 5 are fed into
COMPSOIL, soil displacement for these field conditions is predicted for the high and nor-
mal inflation pressure machine configuration and compares to the measured data as shown
in Figure 80 by the dash-point-dash line. Doing the same with slope and intercept gained
from � of 4, the prediction compares to the measured data as shown by the dashed lines in
Figure 80. When comparing the effect of � to the predictions for both inflation pressures,
� of 4 is closer to the measured data and therefore on the clay soil this appears more ap-
propriate. Predictions of contact pressure from COMPSOIL are probably better close to the
recommended inflation pressure explaining the closer fit to the data of the appropriately
inflated tyre.
Ph.D. Thesis Dirk Ansorge (2007)
115