Model tests of the barrier measures on moisture and salt migration in soils subjected to freeze-thaw cycles

The migration and accumulation of chlorine salt in frozen soils will cause corrosion to the buried pipeline and seriously affect its service life. In order to investigate the effect of moisture and salt migration and accumulation on pipeline corrosion, three models of barrier measures were established using similar criteria, namely, nonsaline soil replacement model (M1), non-saline soil replacement with impermeable geotextile barrier model (M2), and gravel replacement model (M3). Laboratory model tests were carried out to study the characteristics of moisture and salt migration and the barrier effect of different measures in response to freeze-thaw (F-T) cycles. The freezing depth is 38.6, 29.7, and 43.5 cm in three models. The volumetric moisture contents and salt concentrations are positively and negatively correlated with temperature, respectively. In M1, the maximum moisture contents decrease and increase obviously inside and outside of the upper boundary, with the variation rate of 11.7% and 11.1%. The maximum salt concentrations decrease by 7.7% and increase by 1.31 times, respectively. The concentration variations of the lower boundary are not obvious. They remain essentially constant in M2, i.e., 0.323 and 0.039 mol kg-1. The salt concentration in M3 has a far less reduction rate of 4.0%. Impermeable geotextile barrier and gravel replacement can prevent moisture and salt migration and corrosion to the pipeline. Concentration variation of M1 is primarily influenced by convection, salt expulsion and diffusion, while that of M2 outside the upper boundary is only influenced by convection, and M3 is caused by convection and salt expulsion. A combination of M3 and M2 measures are required when the buried pipeline is located above the freezing front and the water table is shallow. In other cases, M2 measures are chosen. The results can provide theoretical support and technical guidance for more economical and efficient construction and safe operation of the buried pipeline.