Cranfield University

Soil Compaction Models
however, the overlying layers can be compacted significantly more. The general influence
of water content on predicted soil displacement was shown by Defossez et al. (2003) who
further improved SOCOMO with respect to water content. Still with adjusted parameters,
the deviation between measured and predicted values was larger than the 95%- CI.
From all the studies into soil mechanical parameters, it can be concluded that an in-situ
approach to determine VCL parameters from tyre passes would be beneficial.
6.1.4 Basic Considerations on the Modeling of Soil Compaction
The fact that plenty of work was conducted concerning the prediction of soil compaction
while at the same time no model is able to suit different conditions entirely rose the ques-
tion why this is the case. Basically soil can be regarded as a granular media and it should
obey the physical laws of granular media. Therefore the author did an extended literature
review concerning the physics of granular media. A summary of the most recent findings
was edited by Hinrichsen and Wolf (2004). Most research was done concerning the flow of
granular media. At the peak of the review the author read an article by Haff (1997) con-
cerning the difficulties in predicting the behavior of geological granular systems. Haff
(1997) points out the fact that the prediction is difficult “not because of the lack of knowl-
edge in physics of geologists, rather because of a complex behavior of environmental ma-
terial (sand, soil, galaxies etc.)”. If a granular medium consists of a well grained and
evenly shaped powder, physical laws can be developed and the material obeys these laws.
However, as soon as either the powder is not well grained and/or not evenly shaped these
physical laws cannot be transferred one to one onto a different powder as the variables
triggering this behavior cannot be either specified accurately or even specified. The follow-
ing example points out this behavior excellently. In pure water one molecule is identical
with another. Each has the same shape, size and weight. However, already sand, which in
soil scientist circles is regarded as uniform and “easy” to predict, differs from one grain to
another in mass, size, shape, and friction. Thus all these values have to be averaged and a
particular investigation in a controlled laboratory environment can be repeated as long as it
is possible to keep the average values sufficiently close. The behavior of the naturally best
sorted and particularly well grained sand dunes is difficult to predict even after in depth
investigations. Thus, moving from sand to soil adds the difficulty of non identical grains as
size distribution varies a lot and does not merely contain sand. Thus the shape of the parti-
Ph.D. Thesis Dirk Ansorge (2007)
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