With the assumption that the compaction index (K) of the tests with two different
containers was the same (compaction method: wall-effect steel fibres), the wall-effect of
the fibres was calculated. The virtual packing density (Equation 4.13: β) is the same in
both containers but unknown. The actual packing density was replaced by the mean
packing density of each container, which is affected by the walls of the container
(Equation 4.7). The influencing area within which the fibres disturb the packing density
was assumed to be the complete fibre length; the top and the bottom of the container
were assumed to be walls, too. With the previous assumptions a single equation was
obtained with two unknown parameters: the wall-effect and the virtual packing density.
A numerical solution was obtained with the Excel-solver and the criterion that the virtual
packing density had to be the maximum; Appendix C (Table C1) summarises the
results. Fig. 4.2 shows the wall-effect of steel fibres (kSF) within an area of one fibre
length (Dramix 45/50 was not tested).