Freeze-thaw deterioration of saline earthen sites under snowmelt or rainfall infiltration

The changes of samples after freeze-thaw cycles under the initial conditions of snowmelt or rainfall infiltration are characterized considering the water content, conductivity, elastic wave velocity and unconfined compressive strength. Furthermore, the freeze-thaw deterioration mechanism of the saline earthen sites is studied based on the macroscopic and microstructure changes of the samples. The results show that during the freeze-thaw cycles, the water content of the samples increases first, then decreases and tends to be stable due to the water supply and evaporation loss of snowmelt and rainfall infiltration, and after migration with water, the salt is enriched at the height of 5 and 3.5 cm, respectively. The supplied water increases the thickness of bound water film between soil particles, and the elastic wave velocity and unconfined compressive strength of the samples decrease significantly. With the progress of freeze-thaw cycles, the water evaporates, and the wave velocity and strength of the samples increase gradually. The salt content and precipitation form are the key factors affecting the strength recovery of the samples. When its content is more than 0.4%, the increase of the content of Na₂SO₄ will reduce the strength recovery ratio of the samples. The addition of NaCl improves the strength recovery ratio of the samples, but slows down the strength recovery rate. After 12 freeze-thaw cycles, the snowmelt infiltration makes the soluble salt fully disperse in the samples, which is conducive to the recovery of soil, the accumulation of water and salt at the top of the samples leads to the formation of salt efflorescence and rolled mud. The rainfall infiltration makes microcracks develop and the proportion of macropores (> 16 μm) increase, the accumulation of water and salt at the wetting front leads to transverse cracks at the side of the samples, and the strength recovery speed and amplitude of the samples are small.