Cranfield University

Appendix
11.1.4 In-field determination of VCL
This section contains the data from field experiments and the approach to gain the slope and
intercept from tyre passes as explained in Section 6.3 will be validated on a clay soil and a
sandy loam soil. On both soils concentration factors of 4 and 5 will be compared. On the
sandy loam three VCLs are gained from shallow tilled and subsoiled soils and by pooling the
data from both treatments.
11.1.4.1 Clay Soil
The approach of defining a VCL from contact pressure and rut depth was also verified with
the field experiments. On the clay loam from rut depths of 57.5 mm and 82 mm for low and
high inflation pressure, respectively, an average increase in DBD of 9.6 and 13.7 % was
calculated assuming 600 mm of uniformly increased DBD. Initial DBD was 1.27 g/cm 3 and
resulted in 1.911 and 1.843 relative density 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 a concentration factor of 5 following the calculations
given in detail in Section 6.3.2. At a concentration factor of 4 the corresponding pressures
were 57.5 kPa and 60.8 kPa. In Figure 17 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 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 17: VCL for clay soil gained in field experiment
Ph.D. Thesis Dirk Ansorge (2007)
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