Research On Freeze-thaw Damage Of Short-term Frozen Soil And Stability Of Shallow Slope

In the short-term frozen ground where the winter temperature is low,the temperature difference between day and night is big and the environmental temperature fluctuates frequently around zero,its unique climatic characteristic includes that the cycle of the formation of frozen soil is short,the behavior of the freezing and thawing is frequent,the thickness of frozen soil is thin and the moisture content of the shallow soil of cutting slope is high after melting snow and ice,and so on.The shallow soil of cutting slope subjected to frequent freezing-thawing cycle and the slope occurs shallow sliding constantly,hence,there is a great influence on the road environment and its operation,but the corresponding research is obviously inadequate.Therefore,researching on the damage effect of the freezing-thawing cycle on the shallow soil of slope and the stability of shallow slope in the short-term frozen ground is necessary.On the ground of systematic summary and in-depth analysis of the domestic and foreign research results of freeze-thaw damage of soil and freeze-thaw slop landslide,the paper designs the freeze-thaw cycle test,triaxial and direct shear test of remoulded triaxial specimen,the direct shear specimen and freezing-thawing interface specimen in order to find the damage process,damage mechanism and establish the damage model after comparing and analysising the experimental datas.Based on the test datas and established damage model,using large-scale non-linear finite element software ABAQUS to simulate and calculate the slope safety factor of short-term frozen slope suffered freezing-thawing damage,summarizing the mechanism of shallow slope instability,and putting forward some corresponding prevention measures.In this paper,the main research conclusions are as follows:1.The freezing temperature of the residual soil increases with the increase of moisture content and the decrease of the salt content of the specimen.The freezing temperature of the sample whose moisture content is 16₅%,19.5%and 21.5%is-1.47℃-1.33℃ and-1.11℃,respectively.2.Based on the same test condition,the test results coming from the freezing-thawing and triaxial shear test show that the damage range of elasticity modulus,breaking strength,cohesion and internal friction angle of the freezing-thawing samples increase with the rise of the negative temperature,the increase of moisture content and the number of freezing-thawing cycle,and the mechanics properties of soil tends to be stable after 7 times freeze-thaw cycly.;the damge range of the cohesion is bigger than the internal friction angle and the difference of the damage rate between them reach up to 36.71%;summarizes the damage mechanism of the soil and put forward the damage model of soil basede on the test data.3.Experiencing the same freezing and thawing,for the same initial condition of the common soil specimen（without freezing-thawing interface）and freezing-thawing interface sample,the shear strength of the freezing-thawing interface sample is bigger than the common soil specimen,the difference of the damage rate of the cohesion and internal friction angle between the two different sample reach up to 22.3%and 5.51%,respectively,the results show that the freezing-thawing interface is not the weak interface;After freeze-thaw action,the shear strength indexes of both ordinary soil specimen and freezing-thawing interface sample suffer damage,and both of their damage extent and the negative temperature,the moisture content,and the freezing-thawing cycle number have negative correlation.4.For the same initial condition of the triaxial soil specimen and the direct shear sample,after experiencing the same freeze-thaw cycle number,the cohesive force obtained from triaxial shear test is greater than the cohesive force obtained from the direct shear test,while the internal friction angle shows opposite tendency that the former is less than the latter.5.The simulated results from the finite element numerical analysis software ABAQUS show that the freezing-thawing action will only reduces the stability of the shallow slope,but has weak effect on the overall stability of slope;the stability of the shallow slope is primarily influenced by negative temperature,moisture content,and freezing-thawing cycly number.For the high moisture content shallow soil slope,the damage effect of freezing-thawing behavior may cause the shallow slope destabilization.Based on the short-term climate characteristic,the economic benefit and the ecological protection,putting forward protecting measure including drainage measure,insulation measure and soil-stable measure to guarantee the stability of the shallow slope.