Using X-ray computed tomography to evaluate the initial saturation resulting from different saturation procedures

One of the parameters needed for characterizing soil hydraulic properties is the
saturated water content. In the past, different techniques have been employed to obtain
an initially fully saturated sample, but it is uncertain how successful the different
techniques actually are in achieving full saturation. In this study three techniques often
applied in the laboratory have been evaluated for a fine sand sample: (1) venting of the
sample with carbon dioxide prior to saturation, (2) applying vacuum to the sample in the
beginning of the saturation procedure, and finally (3) the use of degassed water for
saturation. Evaluation of the different enhanced saturation techniques was done with Xray
computed tomography (CT) and gravimetrically. The use of CT scanning makes it
possible to observe the spatial distribution of wetting and non-wetting phases in the
porous medium in a non-destructive way. In this case the sample was scanned in 1 mm
intervals over the height of the 3.5 cm tall sample, providing detailed information on the
performance of the different procedures. Five different combinations of the above
mentioned saturation procedures were applied to a disturbed silica sand sample. The
sample was drained with pressurized nitrogen between each saturation and allowed to
saturate for the same length of time for all the different procedures. Both gravimetric
measurements and CT attenuation levels showed that venting the sample with carbon
dioxide prior to saturation clearly improved initial saturation whereas the use of
degassed water and vacuum did not improve the saturation significantly.