Cranfield University

Ancillary Experiments
7.3.4.3 Contact Area vs. Perimeter
These results show no coherent picture for the small scale plates between contact pressure,
LPPL, and soil density increase. Therefore in Figure 127 LPPL is plotted against contact
pressure for the soil bin experiment and shows two near linear relationships depending on
axle load. If both, the contact pressure and LPPL data are divided by the corresponding
load resulting in perimeter length and contact area which is plotted on the right hand side
of Figure 127, their relationship appears to be linear. To ease further comparison, soil den-
sity increase will now be corrected for its influence of load, too.
Load per Perimeter Length (t/m)
3,2
3,0
2,8
2,6
2,4
2,2
2,0
1,8
1,6
1,4
1,2
60 80 100 120 140 160 180
Contact Presssure (kPa)
Ph.D. Thesis Dirk Ansorge (2007)
Perimeter Length (m)
6,5
6,0
5,5
5,0
4,5
4,0
3,5
3,0
2,5
164
2,0
0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6
Contact Area (m 2
Contact Area (m )
2
)
Figure 127: LPPL vs. contact pressure (left) and perimeter length vs. contact area
(right)
7.3.4.4 Interaction of Contact Area and Perimeter
Since the previous Sections implied that both contact pressure and LPPL appear to have an
influence on soil density increase, the following model was tested next on the soil bin ex-
periment:
Rel . DensityIncrease
� ContactArea
� PerimeterLength
� ContactArea
* PerimeterLength
Eq. 10
The resulting prediction of the soil density increase is shown on the left of Figure 128
whereby a high correlation coefficient was achieved and the slope was equal to one. How-
ever, following the statistical analysis, the parameter “contact area” dropped out of this full