Study On Mechanical Properties Of Sandy Loess And Slope Stability Under The Action Of Freeze-thaw Cycles

Freeze-thaw is an important reason for the deterioration of the strength of the sandy loess in the Zizhou area of northern Shaanxi Province,where the physical and mechanical properties of the sandy loess are special.In order to make the geological disaster prevention and engineering construction activities in this area better cope with the transformation effect of freeze-thaw on soil strength,this paper takes sandy loess in Zizhou County,Yulin City,northern Shaanxi Province as the research object,conducts freeze-thaw cycles and indoor mechanical tests to study the characteristics of mechanical properties of sandy loess after freeze-thaw under the geological and climatic conditions in this area,and explains the reasons for the change of sandy loess strength from the microscopic perspective,and finally carries out the analysis of the stability of this type of sandy loess slope after freeze-thaw.Finally,the stability analysis of these sandy loess slopes after freeze-thaw was carried out,and the research conclusions have some practical application value.The main work contents and results are as follows:1.For the geological and climatic characteristics of the study area,the freeze-thaw cycle test of sandy loess with changing the number of freeze-thaw cycles,freezing temperature and initial moisture content of the soil was carried out,and the changes in the appearance characteristics of the soil after freeze-thaw were studied,and the causes of the surface structure damage of the soil after freeze-thaw were analyzed.2.By conducting triaxial shear test,consolidation compression test and infiltration test on sandy loess after freeze-thawing,the strength characteristics,shear strength index changes,compression property characteristics and infiltration property changes of sandy loess under the action of freeze-thawing cycles were studied;the influence law of the number of freeze-thawing cycles,freezing temperature,initial moisture content of soil and the coupling between them on the freeze-thawing mechanical properties of sandy loess was analyzed.A model of soil cohesion deterioration based on the number of freeze-thaw cycles and initial water content is established,and the most unfavorable combination of freeze-thaw environment formed by the coupling of initial water content and freezing temperature of sandy loess is proposed;the reasons for the changes of soil mechanical properties caused by the freeze-thaw cycles are analyzed from a qualitative perspective.3.In view of the structural damage phenomenon and mechanical property deterioration of the surface of sandy loess after freeze-thaw,SEM test was used to study the microstructure mechanism of soil caused by freeze-thaw cycle,and the microstructure changes of sandy loess after freeze-thaw were analyzed qualitatively and quantitatively,and the connection between microstructure characteristics and freeze-thaw mechanical properties of soil was established.It is concluded that the freeze-thaw cycle causes the soil structure to be loosened and irregularly developed,and the strength of the soil structure is reduced,which is the root cause of the deterioration of the soil mechanical properties.4.Based on the mechanical parameters of sandy loess after freeze-thaw,the stability characteristics of this type of soil slope under the action of freeze-thaw cycles are simulated and studied using FLAC3 D software;it is found that the freeze-thaw action of the slope surface soil has little effect on its overall stability,and it is believed that the freeze-thaw action mainly adversely affects the slope stability in terms of reducing the strength of the surface soil and enhancing infiltration.5.Combining the analysis results of freeze-thaw mechanical properties and microstructure of sandy loess,the most unfavorable environmental combinations of freeze-thaw cycling action of sandy loess based on freezing temperature and initial moisture content of soil are proposed:both combinations of low moisture content with certain low temperature freezing and high moisture content with extreme low temperature freezing promote the damage of freeze-thaw cycling action on soil structure strength.