Research On Aggregates Stability Characteristics Of Black Soil Under Freeze-Thaw And Freeze-Drying Conditions

The black soil of Northeast China has excellent land resources and is one of the most important grain-producing areas in China.It is located in the seasonal permafrost zone at middle and high latitudes,with long and dry winters and frequent wind and snowfall and rainfall in spring,and the natural climatic conditions are complex,and the black soil topsoil experiences repeated freeze-thaw and freeze-dry effects,which change the soil physical properties and affect the stability of soil aggregates and soil erosion resistance.In this experiment,the typical black soil in northeast China is used as the research object.By conducting indoor simulations of freeze-thaw cycle,freeze-thaw-freeze-dry and freeze-thaw-freeze-dry-freeze-thaw processes,effective indicators such as agglomerate destruction rate and average weight diameter are selected to characterize the stability of soil agglomerates,and the effects of freeze-thaw cycle,freeze-dry action and initial water content of soil on the stability of soil agglomerates are analyzed.The main findings of this paper are as follows.(1)The number of freeze-thaw cycles significantly influenced the compositional characteristics of soil water-stable agglomerates.Under the same initial water content conditions,with the increase in the number of freeze-thaw cycles showed a tendency for the agglomerates to be broken into smaller agglomerates with smaller particle size.The water stability and fragmentation of agglomerates were also influenced by both the number of freeze-thaw cycles and the initial water content,with the increase of the number of freeze-thaw cycles and the water content,the fragmentation rate and the average weight diameter of agglomerates with higher initial water content changed more than those with lower water content,which showed that the fragmentation effect of agglomerates with high water content was obvious,the average weight diameter decreased significantly,and the content of large agglomerates decreased.Overall,the water stability of the agglomerates decreases with the increase of the number of freeze-thaw cycles and the initial water content.(2)The freeze-drying effect and the number of freeze-thaw cycles jointly affect the composition characteristics of soil water-stable agglomerates.Freeze-drying increased the content of large agglomerates to a certain extent when the water content was low,but with the occurrence of freeze-thaw cycles and the increase of initial water content,the freeze-drying effect might be beneficial to increase the adhesion between soil grains,and the agglomerate stability was slightly enhanced compared with the time when freeze-drying did not occur.The analysis of the data shows that freeze-drying causes significant fragmentation of >5 mm agglomerates and has a more significant effect on agglomerates with high water content,and freeze-drying on the basis of freeze-thaw cycles leads to increased agglomerate fragmentation and negatively affects the water stability of soil agglomerates.(3)The overall content of large agglomerates decreased significantly under the coupled freeze-drying-freeze-thaw conditions,while the content of small agglomerates increased significantly at higher water contents.The freeze-thawing-freeze-drying-freeze-thawing process reduces the destruction rate of small agglomerates and increases the average weight diameter,probably because after freeze-drying,the agglomerates are replenished with certain water for freeze-thawing,and at this time,after one freeze-thawing,the water stability index of the agglomerates with low water content does not change significantly,when the water content increases,the number of freeze-thawing cycles increases,the soil structure changes drastically,the average weight diameter decreases significantly,and the overall water stability of the agglomerates decreases significantly.The overall water stability of the aggregates showed a significant decrease.