Experimental Study on the Salt Migration Behavior of Coarse-Grained Saline Soils Subgrade under Strong Evaporation Environment

This paper studied saline soil’s water and salt migration behavior under evaporation conditions by a self-designed experimental device, and the evolution law of the water content, conductivity, and temperature in different heights of saline soil roadbeds was analyzed. The test results show that at an ambient temperature of 18°C, the water-salt migration of saline roadbed is mainly concentrated in the early stage of hydration (≤48 h), which shows a typical phenomenon in which salt in the soil follows the water and the conductivity of soils increases synchronously with the water content. Under the evaporation condition, the decreased rate of water content was accelerated in the sample area near the heat source, resulting in a constant increase in the rate of conductivity and a wider salt aggregation area. Further, a critical subgrade height prediction model is established based on the maximum salt and water migration height in saline soil roadbeds with the help of Hydrus numerical simulation software. The model analysis results show that the migration rate of salts gradually lags behind that of water because the burial depth of groundwater increases under evaporation conditions. When the burial depth of groundwater is <1.5 m, the change of water-salt migration of the roadbed is gradually stabilized, and the height of salt erosion area on saline soil roadbed no longer rises. The research conclusions can guide the design level of the structure of saline soil roadbeds under evaporation conditions.