Stability Analysis Of Seasonal Frozen Soil Slope In West Sichuan During The Thawing Period

In recent years,with the proposal of national transportation strategy,a large number of transportation infrastructures have been built in the seasonal frozen soil area of Western Sichuan.Natural slopes,road and railway slopes in the region often collapse during the thawing period of the following year due to freezing and thawing,resulting in huge economic losses and safety accidents.In order to effectively solve the freeze-thaw collapse disaster of seasonal frozen soil slopes,this paper takes the mixed soil slope widely distributed in the seasonal frozen soil region of Western Sichuan as the research object.Through the combination of experimental measurement,theoretical analysis and numerical simulation,the stability and instability mechanism of seasonal frozen soil slope in thawing period are studied,which provides a certain reference for practical engineering.The main research contents and achievements are as follows:(1)Through the experimental research on the engineering characteristics of the unsaturated mixed soil in the seasonal frozen soil area of Western Sichuan,the density,moisture content,particle gradation and permeability coefficient of the sample are determined,and the effect of the percentage of coarse particles and moisture content on the shear strength parameters of the mixed soil samples is analyzed.As the content of coarse particles increases,the cohesive force of the sample gradually decreases and the internal friction angle gradually increases.As the moisture content increases,the cohesive force and the internal friction angle of sample gradually decrease,and the decrease of cohesive force is significantly greater than that of internal friction angle.(2)Based on the theory of frozen soil thermal-hydraulic coupling,the thermal-hydraulic coupling model of seasonal frozen soil slope is established,and the changes of temperature field and water field of the slope in the process of freezing and thawing are calculated by COMSOL software.According to the analysis of temperature field,the maximum freezing depth during the freezing period is about 1.1 meters,and the freezing-thawing interface decreases gradually in the thawing stage,and the soil is completely thawed in late March.Through the analysis of moisture field,it is concluded that the unfrozen water in the soil gradually migrates to the freezing front in the freezing stage,which slightly increases the water content of the soil in the freezing area.In the thawing stage,the shallow frozen soil and snow on the slope gradually melt,which sharply increases the water content of the soil above the freeze-thaw interface,and forms a transient saturated zone with a thickness of about 0.85 meters in the shallow layer of the slope.(3)A calculation model for the stability of seasonal frozen soil slopes that comprehensively considers the coupling effects of thermal-hydraulic is established,and the stability coefficient of seasonal frozen soil slope decreases gradually during the thawing period.By analyzing the displacement and plastic deformation of the slope to determine the position of the sliding surface,and compared with the temperature field,it is concluded that the position of the potential sliding surface of the slope during the thawing period is basically the same as that of the freeze-thaw interface,and the trend of the potential sliding surface is roughly parallel to the slope surface,which belongs to the plane sliding type.(4)Analysis of the slope instability mechanism and factors of affecting stability show that the melting of frozen soil during the thawing period and the infiltration of snow melt are the main reasons of shallow collapse of seasonal frozen soil slope in Western Sichuan.Soil coarse particle content,initial water content and slope have a greater impact on slope stability.The lower the soil coarse particle content,the more the initial water content,the greater the slope,and the worse the overall stability of the slope after the frozen soil has melted.