Evidence of pressure jump signatures linked to fast air-water displacement dynamics in macropores

We present a method to identify the characteristics of pressure jumps in repeated pump-driven saturation and drainage cycles in packed sand columns, i.e., pore pressure from zero to -80 hPa. This method is based on the registration of pore pressure oscillations using high sensitivity and rapid response tensiometers. The pressure signals were processed to identify and extract the pressure waveforms read by two tensiometers simultaneously. Then, the waveforms were classified by k-means clustering algorithms and principal component analysis. We obtained a classification of different types of pressure waveforms that are consistent throughout successive cycles of wetting and drainage cycles. This consistency can be associated with patterns of fast capillary displacements in macropores, and ultimately, to hydrodynamic features of the structure.