Abstract: To investigate the unsaturated wetting deformation of loess, staged water-saturation test is conducted on loess specimens of different compactness degrees. The critical void ratio for the wetting deformation of compacted loess is proposed by comparing the deformation behaviors of loess among different stages from unsaturated to saturated state. In addition, scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP) are adopted to analyze the correlation between wetting deformation behavior and microstructure evolution. Results are concluded as follows: 1) under a constant vertical pressure, the void ratio of loess specimen decreases exponentially with the rising of saturation degree and finally reduces to the critical void ratio when its corresponding initial void ratio is greater than critical void ratio; while when initial void ratio is lower than critical void ratio, void ratio exhibits no change. 2) When the compactness degree is 70%, strong wetting deformation is resulted from large amounts of inner pores with sizes larger than most particle sizes, while loess with a compactness of 90% presents an opposite trend. 3) Under loading and wetting actions, the pore structure of loess with a compactness of 70% varies significantly, with particles getting rounded and particles’ predominant orientation reinforced; while for loess with a compactness of 90%, the pore structure changes slightly with no obvious change in particles’ predominant orientation, and particles tend to be angular due to the weak cementation among particles.

Key words: compacted loess, unsaturated, wetting deformation, critical void ratio, microstructure