Microstructure and compressibility evolution of sulfate saline compacted loess under drying-wetting cycles

Soil salinization not only can induce environmental problems but also cause notable changes in the engineering performance of soil, especially the compacted loess that is often exposed to drying-wetting (D-W) cycles in Northwest China. To explore the changes in compression behavior of the saline compacted loess under D-W cycles, a series of the oedometer tests were conducted on compacted loess samples with different D-W cycles and sodium sulfate content. In addition, the changes in microstructural properties of the loess samples were also investigated by scanning electron microscope (SEM) tests. The results demonstrate that the compressibility co-efficient of the loess samples increases with D-W cycles and tend to stabilize after three cycles, while varies linearly with salt content. The compressibility deterioration equation for the based on the compressibility co-efficient was then established considering both D-W cycles and salt content, which can well predict the compressibility deterioration of saline compacted loess under D-W cycles. Due to the repeated gasification and liquefaction of pore water and the repeated dissolution and crystallization of sodium sulfate, the skeleton of saline compacted loess with higher salt contents or more D-W cycles tends to loosen, which greatly enhances the effective connectivity of the pores and leads to the deterioration of compressibility. Finally, the compressibility deterioration ratios due to D-W and salt erosion were discussed by decoupling analysis. These findings can provide references for the engineering practice in loess areas.

Automated summary

Soil salinization has significant effects on the engineering performance and microstructural properties of loess. The compressibility of loess samples deteriorates with increasing drying-wetting cycles and salt content, and the compressibility coefficient shows a linear relationship with the salt content. The enhanced effective connectivity of pores in saline compacted loess is the main reason for the deterioration of compressibility.