Experimental Study on the Effect of Freeze—Thaw Cycles on the Mineral Particle Fragmentation and Aggregation with Different Soil Types

The freeze–thaw cycle can change the size and shape of soil particles, that is, cause fragmentation and aggregation of soil mineral particles, thereby affecting the soil structure, which, in turn, affects the soil properties. In addition, the process of soil mineral fragmentation and aggregation, as an event closely related to the cold climate, plays an irreplaceable role in reconstructing the climatic conditions of a certain area and a certain period of time and has important referential significance for the restoration of historical permafrost boundaries and the study of climate change. Therefore, in order to better study the effect of freeze–thaw cycles on the fragmentation and aggregation of soil mineral particles, four soil specimens were selected for this study: the freeze–thaw cycle tests were carried out 0, 3, 6, 9, 50, and 100 times, respectively, and the test results were analyzed. The results of these experiments indicate that (1) after freeze–thaw cycles, the changes in grain-size distribution are different in various soil types, and the changes are mainly concentrated in 0.001–0.1 mm: (2) the coarse particle size particles (sand, silt) can be fragmented into relatively fine-grained particles (silt, clay). The fine-grained particles (clay) cannot undergo fragmentation, and the decrease in clay is due to its aggregation: (3) with the increase in freeze–thaw cycles, the fraction change trend of four specimens is parallel to the x-axis, which means the fragmentation and aggregation of soil mineral particles are in a state of equilibrium or balance: (4) the increase in the Kvar value indicates the change in grain-size distribution, which means aggregation and fragmentation of soil mineral particles. After the 100th cycle, the Kvar value of four specimens is &lt:0.1, which belongs to a low-intensity area: (5) the freeze–thaw cycle will change the type of soil, and after 100 freeze–thaw cycles, the soil type of specimen (H) changes from silty clay loam to silty clay: (6) during the freeze–thaw process, different types of soil have different situations of aggregation and fragmentation.