In order to find the mechanism of the effect of freezing and thawing circulation on the cohesion of saline soil

saline soil samples have been tested in laboratory. By analyzing the variation of the crystalloid location

the microstructure

the salt property and unfreezing water content

the mechanism between freezing and thawing circulation and cohesion is obtained. The research results show that while moisture content is constant

adding either sodium sulfate (Na2SO4) or calcium chloride (CaCl2) to the soil samples

the cohesion reduces with freezing and thawing time increasing. And the primary phases of cohesion reduction are the first and second circulation. The degree of cohesion reduction by adding CaCl2 is minor than adding Na2SO4. The main reason of the reduction of both cohesion and density is that the variation of the crystalloid location occurs while they separate out during freezing and thawing circulation. From the scanning electron microscope (SEM) graph

it is easy to find out that the proportion of big pores of the samples shrink with freezing and thawing circulation time increasing. The content of CaCl2 solution in saline soil has an important influence on the cohesion variation in freezing and thawing circulation.