Model Test Study On Stability Of Unsaturated Expansive Soil Slope Under Freeze-thaw Cycles

Expansive soil is widely distributed in the seasonal frozen soil regions in China,and freeze-thaw cycle is an important disaster inducement for expansive soil slope.This article focuses on the stability of expansive soil slope in the seasonal frozen soil area under freeze-thaw cycles,under the premise of mastering the basic physical and mechanical properties of expansive soil,a large-scale slope model combined with emperature and humidity fields.The coupling analysis methods are adopted to study the effects of freeze-thaw cycles on the crack,displacements,soil pressure and moisture content of slopes under different initial moisture contents,different slope ratios,and whether they are reinforced.To understand the variation of physical properties of different initial moisture contents and slope ratios under freeze-thaw cycles,and to clarify the effect of geogrid on the displacement of expansive soil slope and the effect of improving slope stability.Soil slope engineering provides a theoretical basis.(1)Expansive soil is a typical unsaturated soil,which is composed of solid soil particles,water and gas,the freeze-thaw cycle change the three-phase volume.The development of the crack tend to decrease with the increase of initial moisture contents.Under the freeze-thaw action,the expansion of the three types of soil slopes with an initial water content increases the soil pressure with decreasing temperature and vice versa.However,the overall trends of soil pressure at different initial water contents slopes are different;The 20% and 30% moisture content slope displacements show a“frost shrinking and thaw expanding” phenomenon under a single freeze-thaw action,the 40% moisture-content slopes show a “frost expanding and thaw shrinking”phenomenon,The slope displacement of three kinds of initial moisture contents shows the trend of gradual deformation to the face;the higher the moisture content,the slower the temperature conduction,and the longer it takes to reach 0 ? during the thawing process;the moisture content decreases with the decrease of temperature and rises with the increase of temperature under freezing and thawing.The higher the initial moisture content,the greater the change in moisture content after freezing and thawing;the higher the initial moisture content,the worse the carrying capacity of the soil after thesame number of freeze-thaw cycles.(2)Slope ratio is a factor that must be considered in practical slope engineering.Under the action of freeze-thaw cycle,the crack width and crack depth are proportional to slope ratio.The maximum change value of the slope displacement of the slopes with slope ratios of 1:1.5,1:1 and 1:0.5 decreases in the first freezing process.A large slope ratio and a small lateral length of the slope cause the temperature conduction rate to increase with the increase of the slope ratio;The slope of 1:1.5 slope ratio has an increasing trend in the freezing stage of-10 ?,the slope of the 1:1 slope ratio has a stable stage in the freezing stage at-10 ?,and the moisture content of 1:0.5 slope ratio slope tends to decrease during the freezing stage of-10 ?.(3)The mechanism of the effect of geogrid on the shallow stability of expansive soil slope under freeze-thaw cycles is that the reinforcement at the interface of the reinforcement will restrict the movement and rotation of the soil particles,and provide“interface friction” to soil.this has the effect of improving the stability of the slope.The geogrid can well suppress the horizontal and vertical crack development and vertical displacement changes of the expansive soil slope due to freeze-thaw cycles.And geogrids limit water migration by increasing migration paths and reducing permeability.