Experimental investigations of the soil water retention curve under multiple drying–wetting cycles

Natural soils usually experience multiple drying and wetting cycles in geotechnical engineering. In this paper, the influences of history of drying and wetting upon the desorption and adsorption soil–water retention curve (SWRC) of silicon micro-powder (SMP) and Guangxi Guiping clay (GGC) are examined and discussed. The experimental results presented are obtained by using an improved pressure-plate instrument. The results show that the size of the hysteresis loops decreases with increasing drying–wetting cycles, and these are almost identical after 4 drying–wetting cycles. In addition, the all drying–wetting curves are best fitted by VGM model, and the estimated drying air-entry value reduces with the drying number and remains almost unchanged in the fourth and fifth drying. On the contrary, the wetting estimated air-entry value increases with the wetting number and tends to a stable value.