Study On The Mechanism Of Salt Erosion Damage Of Loess Under Freezing Thawing

The erosion effect of soluble salt in loess has an adverse effect on the structure of loess.Under the influence of factors such as freezing thawing cycle and water content,it will induce the collapse of loess body.Based on the salt inhibition on the loess landslide body cognitive mechanism is not entirely clear,this paper carried out the freeze-thaw test of undisturbed loess salt,the salt content,water content,freeze-thaw cycles and other factors analysis of undisturbed loess,the occurrence mechanism of salt corrosion type collapse disaster.Taking the intact loess of Xi'an,Shaanxi as the research object,this paper studies the strength degradation characteristics of different saline original loess after experiencing different freeze-thaw cycles.the damage degree of cohesive force of soil samples under the effect of frost heaving and salt erosion is analyzed and compared.The intact loess in Xi'an,Shaanxi is taken as the research object.The raw salt soil with different gradient salt content was made by adding different proportions of Na₂SO₄ to raw soil sample by self-made sponge leaching salt method??=0.0%,0.5%,1.0%,1.5%?.The freezing and thawing cycle was carried out,and the strength parameters of soil samples were obtained by three axis shear test.The results show that with the increase of the number of freeze-thaw cycles,the salt loess cohesion change trend of exponential decay approximation,and the attenuation is mainly concentrated in the first,second cycle;with the increase of salt content,salt loess cohesion change trend of parabola approximation decay,and the attenuation increases with increasing moisture content;the salt loess cohesion change trend of approximate linear attenuation;Under the premise of only considering two kinds of destruction factors,frost heave and salt expansion,with the increase of freeze-thaw cycles,the strength damage caused by high salt??=1.0%,1.5%?content is relatively large,which is more than 50%.The strength damage caused by low salt??=0.5%?content is always lower than that caused by frost heaving.With the increase of salt content,the proportion of freeze-thaw damage to salt erosion is parabolic.The former presents an upward and downward gradual decline,and the latter presents a gradual upward downward section.The damage law of the strength of the salt containing loess is very complicated by the freezing and thawing cycle.The BP neural network algorithm is used to train the test data,and the prediction model between the factors and the shear strength indexes is obtained.It is found that the relative error between the predicted values and the experimental values of the cohesive force of the Loess containing cohesive salt is very small during the freeze-thaw process,which indicates that the model has good prediction accuracy and can comprehensively describe the quantitative relationship between various factors and cohesive force.Under the action of frost heaving and salt erosion,the internal structure of the Loess body is constantly changing.In this paper,the microcosmic damage process of the loess soil with different freezing thawing cycles and salt content is studied by CT micro test.The results show that with the increase of the number of freeze-thaw cycles,the number of CT ME salt in the undisturbed soil sample showed changes similar to the strength of the exponentially decreasing approximation;the CT number and SD value increased with the increase in the number of freeze-thaw cycles,and atherosclerotic changes of stress strain curve approximation.