Hysteresis of saturation-capillary pressure relations under consecutive drainage-imbibition cycles in fine sandy medium

The hysteresis of saturation-capillary pressure (S-p) relations was investigated in a fine sandy medium under consecutive drainage-imbibition cycles, which resulted from scheduled water level fluctuations. A drainage-imbibition cycle starts with a drainage process and ends with an imbibition process in sequence. The saturation and capillary pressure were measured online with time domain reflectometry (TDR) probes and T5 tensiometers, respectively. Results show that the relation between the degree of hysteresis and the number of the drainage-imbibition cycles is not obvious. However, the degree decreases with the increase of the initial water saturation of the imbibition processes in these drainage-imbibition cycles. The air-entry pressure of a sandy medium is also found to be constant, which is independent of the drainage-imbibition cycles and the initial water saturation of the drainage process. In all the imbibition processes, parameter α of the van Genuchten (VG) model decreases with the increase of the initial water saturation, which corresponds positively to the magnitude of the hysteresis.