Variability Study Of Non-collapsible Loess-like Soil Of Changchun Under Freeze-thaw Cycles

In cold regions, the soil would undergo periodic freezing and thawing because ofthe cyclical change of climate with atmospheric temperature. It is an important reasonthat is freeze-thaw cycles as strongly weathering process for causing the soildegradation, intensely changing the structure of soil. The paper summarized the lawand searched for the quantitative method about the change of the micro-structure andmechanical properties of soil for the frost heave and thaw. There has a very importantsignificance for the development of frozen soil mechanical and the engineeringconstruction in the cold region through studying the changing law of physical andmechanical properties of soil due to freeze-thaw cycle.Generally, the loess-like soil is not collapsible in Changchun region, the reasonsare that some factors make the collapsible speed slow or even disappear, the mostimportant high clay content, less soluble salt content and high water content. However,Changchun is located in northeast cold regions, freeze-thaw cycle tends to exacerbatethe deterioration and destruction of loess-like soil and also make the inter moistureredistribution and the pore size and particle change. Therefore, it is necessary to studythe influence of freeze-thaw cycle on the physical properties, micro-structure andcollapsible of the loess-like soil.Many scholars have done a lot of study about the effect of the freeze-thaw onloess-like soil of Changchun region. These researches focus on the migration ofmoisture, salinity change and temperature change, etc. However, there are fewliteratures involving the change of engineering properties of loess-like soil. The papermainly studied the influence of freeze-thaw cycle on the physical and mechanicalproperties of loess-like soil in Changchun region, including, particle composition,liquid and plastic limits and collapsible characteristics, and revealed the affectingmechanism from the perspective of the micro-structure.The test loess-like soil samples were taken from Changchun region. The sampling depth of underground is5m in which soils have never experiencedfreeze-thaw cycles in its natural state. Then, artificial samples were prepared, whichhave the same dry density and different water content with undisturbed samples. Allsamples performed freeze-thaw cycle test (the number of freeze-thaw cycle are0,1,3,6,10,15and20, respectively) under the condition of different initial states,namely the same dry density and different water content, and the freezing temperatureis-23℃and the thawing temperature is room temperature. A freeze-thaw cycle is48h.Further, collapsible tests were carried for the samples, and the qualitative andquantitative analyses were performed for the changing characteristics ofmicro-structure before and after freeze-thaw cycle by using scanning electronmicroscopy and mercury analyzer.Through preliminary studying the effect of freeze-thaw cycle on themicro-structure of loess-like soil of Changchun region, as well as causing thevariation of physical mechanical indexes and collapsible, this paper reveals theinfluencing mechanism of freeze-thaw cycle on the collapsible and establishes thequantitative relationship between the number of freeze-thaw cycle and the physicalmechanical properties.The study indicates that the properties of loess-like soil would be changed underfreeze-thaw cycle in Changchun region. with the increase of freeze-thaw cycle，liquidlimit and plasticity index would reduce for the artificial samples and undisturbedsamples，making original non-collapsible loess-like soil produce collapsible in adegree. Study results provide a new idea for researching the collapsible reasons andmechanism of loess-like soil in the seasonally frozen zone and scientific basis forpreventing collapsible disaster of loess-like soil.