Abstract:

The freeze-thaw action is a particular formation mechanism of the soil salinization. It exhibits special travel law of moisture and salinity that moisture and salinity moved two times in the soil freeze-thaw process, and the structure of soil profile turn into three layers: freeze layer, similar freeze layer and non-freeze layer. In the freeze process, salinity moves up with moisture in-phase, it make salt content increase obviously in the freeze-layer soil. In the thaw process, salinity and moisture cumulated in the freeze-layer soil move up again with evaporation, it makes salinity of the surface layer increase sharply. The result of simulated experiment not only proved the formation process of the soil salinization, but also provided theory for prevention and cure of soil salinization in the freeze-thaw area of north China. 　　In the soil freezing process, salinity accumulates in the frozen frcntal surface along with moisture removing; ice crystal forming and salt separating out. Salinity transfers up into frozen layer by means of film water, which increases rate and quantity of salinity in the frozen top layer. Coming from no freeze layer with capillary water moving up, the salinity accumulate in the frozen layer with moisture freezing mostly. Salinity transfer along with the moisture is pumped into frozen layer, the concentration gradient of salt form in the frozen frcntal surface, which result in freezing point grads. The frozen frcntal surface can jump over the rich salt belt for the descending speed of freezing point is lower than temperature. The alternate layer of frozen layer and no freeze layer appears in the same groundmass. The salinity in the frozen layer still moves up in the freezing process. In the thawing process, soil moisture remove towards top layer and vaporize with top frozen layer thawing, the salinity accumulating in the frozen layer transfer up and cumulate in the top soil layer, which make salinity cumulate in the top soil layer by explosive mode.

Key words: freeze-thaw, moisture and salinity movement, simulated experiment, soil salinization