Water-retention curves of loess under wetting-drying cycles

Water-retention curves (WRCs) of intact, compacted and reconstituted loess were investigated using a pressure plate extractor. All specimens were prepared having the same initial density and subjected to two cycles of drying and wetting in the suction range of 0-400 kPa. Furthermore, their pore-size distributions (PSDs) were measured through mercury intrusion porosimeter (MIP) for explaining the measured WRCs. The results show that the air-entry value of reconstituted loess is 505% and 169% larger than that of intact and compacted loess, respectively. This is because the reconstituted loess has more uniform PSD and lacks large-sized pores, as supported by the MIP measurements. On the other hand, the average degree of hysteresis of reconstituted loess during the second wetting-drying cycle decreases by 73% compared to that of the first cycle, which is attributed to the significant soil shrinkage (i.e. 28%) induced by the first wetting-drying cycle. On the contrary, the number of wetting-drying cycles shows negligible effects on the hysteresis of intact loess. In addition, the wetting-drying cycles influence the hysteresis of compacted loess only in a narrow suction range (i.e. 10-50 kPa).