Drying effect on the microstructure of compacted salted silt

In this study, the drying-induced microstructure evolution of compacted silt with different salinities is investigated using mercury intrusion porosimetry and environmental scanning electron microscope. The pore size distribution (PSD) of specimens compacted near optimum (w = 17%) exhibited bimodal characteristics. Upon drying (w = 8%), the PSD changed to a trimodal pattern with the appearance of a new nano-pore population. This suggested the development of nano-fissures, which could occur in the clay fraction and at the interface between clay particles and silt/sand grains due to the clay shrinkage. With further drying (w = 3%), the nano-pores disappeared and the PSD recovered to bimodal characteristics, suggesting that the nano-fissures created were enlarged until they became micro-fissures. The salinity seemed to decrease the frequency of the drying-induced micro-pores due to the enhanced mechanical strength of salted soil by the soil aggregation resulting from the compression of the diffuse double layer and a possible cementation effect produced by precipitated salt. However, the salinity effect was relatively low, owing to: (a) the low clay fraction (15·7%) and the low-activity clay minerals (illite, chlorite and kaolinite); (b) the low specific surface area (24 m 2 /g), which limited the salinity effect on the diffuse double layer.