What is the impact of entrapped air on the measurement of saturated hydraulic conductivity of soil?

Sammanfattning: 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.