X-ray computed tomography was applied to investigate the influence of entrapped air on standard
laboratory measurements of saturated hydraulic conductivity Ks in five soil samples. The investigation
consisted of five X-ray scans for each sample. Soil samples were saturated by the standard laboratory
method from the bottom at the first step. To attain full saturation and explore the difference of
entrapped air content on the standard laboratory measurements, a vacuum chamber was used to
remove the entrapped air from the initially unsaturated soils and then the samples were again saturated
from the bottom. To measure Ks, a measurement device that is based on a constant-head principle was
applied. The results showed that the volume of entrapped air greatly depends on how the soil was
saturated. Furthermore, the saturated hydraulic conductivity and the entrapped air content were
negatively correlated with a strong Pearson correlation coefficient (rb = -0.6). Thus, not considering
the existence of entrapped air leads to errors in estimating Ks values
