Evolution of Unsaturated Shear Strength and Microstructure of a Compacted Silty Clay on Wetting Paths

Silty clay is a common embankment material whose moisture increases over time due to soil–atmosphere interactions and climate changes. The objective of this study is to investigate the unsaturated shear strength and microstructural evolution of compacted silty clay on wetting paths. Suction-controlled triaxial tests, scanning electron microscopy (SEM) observations, and mercury intrusion porosimetry (MIP) tests were performed on compacted silty clay specimens at various matric suctions and net confining pressures. The results show that both the matric suction and the net confining pressure have positive effects on the unsaturated shear strength of compacted silty clay. Nevertheless, they tend to cause different failure forms of the specimens, indicating distinct mechanisms behind their contributions to the soil shear strength on wetting paths. A change in matric suction does not lead to obvious evolution of clay particle orientation, but an increase in net confining pressure causes a weaker preferential orientation of clay particles. The shape of pore size distribution curves is slightly affected by the matric suction on wetting paths, while an increase in net confining pressure obviously reduces the proportion of large pores. The brittle failure of compacted silty clay appears due to the presence of open microcracks at high matric suctions.