Cranfield University

Ancillary Experiments
axial load was applied as shown in Figure 21 to two plate sizes. Each plate was randomly
laden to either constant or peaked pressure, which resembled the loading cycle as if the
tyre passes the soil, three times. The time integral of pressure was kept identical for both
plates and histories. Thus any difference could only be caused by the difference in pressure
application. The resulting sinkage is shown in Figure 132.
Plate 1 represents a large harvester tyre and Plate 2 represents the contact area of a track. In
both cases the peak pressure causes significantly more sinkage than the average pressure.
This result emphasizes the importance of the peaked pressures. If the pressure history
could be made uniform, the soil displacement could be further reduced. The reduction in
this case would have been approximately 1/3. Therefore it can be concluded that it is bene-
ficial to minimize pressure peaks from undercarriage systems in order to reduce the impact
of traffic on soil.
Sinkage (mm)
14
12
10
8
6
4
2
0
0 0,1 0,2 0,3 0,4 0,5
Peak or Constant Force (kN)
Plate1 Constant
Plate2 Constant
Plate1 Peak
Plate2 Peak
Figure 132: The influence of peak pressure vs. constant pressure while the average pres-
sure is the same both times
7.5 Consideration of Vertical Soil Failure
The vertical soil failure indicated by the vector diagrams of soil movement found after the
passage of tyres and tracks indicated in this work (e.g. Figure 8) and Ansorge (2005, a)
was first reported by Seig (1985) who refered to it as “punching type of soil failure”. Trein
(1995) reported the same characteristic. This characteristic contradicts the soil movement
expected from the pressure bulbs of the theory of Söhne (1953). In the following plate
sinkage and passive earth pressure theory are taken into consideration aiming to explain
the punching failure.
Ph.D. Thesis Dirk Ansorge (2007)
170