Experimental study on the hydraulic conductivity of unsaturated dispersive soil with different salinities subjected to freeze-thaw

The hydraulic conductivity of soil is a fundamental parameter that should be obtained both in hydrological and geotechnical studies since it relates to a series of hazards in earthen engineering projects, whereas investigations on dispersive soils, especially those distributed in cold regions, have rarely been reported. This study aims to explore the characteristics of permeability by using a dispersive soil from northeastern China, as well as the effects of soil salinity and freeze-thaw on the variation in hydraulic conductivity. Indoor constant-head permeation tests were conducted on artificially prepared specimens, and initial soil suctions were measured by the filter paper method to assist the analyses. The results demonstrated that the hydraulic conductivity decayed with permeation time until reaching relative stability, and both maximum and relatively-stable values (k(max) and k(rs), respectively) should be adopted for comprehensively characterizing the permeability of dispersive soils. Increasing salt content increased the k(max) exponentially, and the inflection salt content was approximately 1.5%, from which a sharp increase in k(max) appeared; the k(rs) showed a slight increase with initial salt contents as well. Freeze-thaw yielded nonmonotonic changes in the permeability as k(max) peaked at 5 freeze-thaw cycles; the variation in k(rs) was similar. The osmotic suction positively correlated with k(max) but did not fully contribute to the sharp increase in k(max) since it increased linearly with the salt content without mutation points. The number of freeze-thaw cycles influenced the relationship between the osmotic suction and k(max). The matric and osmotic suctions posed opposite impacts on the permeability. More importantly, detailed discussions for the underlying mechanisms of the abovementioned novel observations were illustrated. These results may serve as good references for understanding the features of the permeability of dispersive soils in seasonally frozen regions domestically or worldwide.