Abstract: In unsaturated soil roadbeds, water migration occurs not only in liquid form but also in gas form. The coupled migration of water vapor can severely impact the long-term stability and service performance of the roadbed throughout its service life. We conducted resistivity tests and water vapor migration tests on representative unsaturated soil roadbeds to investigate the effects of initial water content and initial degree of compaction on resistivity. The aim was to uncover the resistivity variation pattern of unsaturated soil roadbeds during water vapor migration and establish a water content-resistivity model. The results indicate that the resistivity of clayey soil decreases exponentially with an increase in water content and compaction degree. Resistivity is more sensitive to changes in water content. Furthermore, as migration time increases, the resistivity decreases at the top of the soil while increasing at the bottom. Higher initial water content initially intensifies resistivity attenuation at the top of the soil, followed by a subsequent decrease. As for different compaction tests, greater compaction results in a smaller decrease in resistivity at the top of the soil. The calculated results from the resistivity-water content model align well with the experimental data, exhibiting a good model fit.

Key words: unsaturated roadbed, water vapor migration, resistivity, moisture content, degree of compaction