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Fig. 8.24 Details of experimental set-up to measure capillary conductivity. (From Nielsen and Biggar, 1959.)
Fig. 8.25 Capillary conductivity of
Columbia Silt Loam, as a
function of pressure and
water content, as measured
with the apparatus shown
in the previous figure. The
difference between the first
and second drying cycle
was mainly due to the
initial soil consolidation
resulting from the negative
pressure in the water
(1 hPa is roughly
equivalent to 1.02 cm of
water column). (After
Nielsen and Biggar, 1961.)
Determination of the capillary conductivity
In principle, the capillary conductivity can be measured by column experiments, similar
to those conducted by Darcy, provided the water content
or the mean water pressure
p w in the column can be measured or otherwise maintained at the desired value. An
example of such an experimental set-up is shown in Figure 8.24 (Nielsen and Biggar,
1959), and the corresponding measured values of k
θ
) are shown
in Figure 8.25. It can be seen that the relationship between capillary conductivity k
=
k (
p w ) and k
=
k (
θ
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