Experimental Study On The Mesostructure And Mechanical Properties Of Saline (Salinization) Frozen Soil In The Qinghai-Tibet Engineering Corridor

The Qinghai-Tibet Plateau is a typical representative of global high-altitude permafrost,and is also the main distribution area of alpine desert saline soils in China.Under the cyclic action of high-frequency freezing and thawing and high-intensity radiation,the saline（salinization）frozen soil has the dual characteristics of frost heaving and thawing of frozen soil and salt swelling and dissolution of saline soil.It often leads to secondary geological disasters such as thermal thawing and collapse,Salt Lake collapse,and engineering structure diseases such as Road mud boiling,pipeline corrosion and pile foundation cracking,which brings great hidden dangers to the ecological environment protection and Engineering safety operation in this area.Especially in recent years,with the continuous warming of the global climate,the deterioration of permafrost has intensified,and the ecological environment of permafrost has undergone great changes.The area of desertification,desertification,marshification and salinization on the Qinghai-Tibet Plateau has been expanding,and the area and degree of damage caused by saline（salinization）frozen soil has also continued to increase.Based on this situation,it is of great engineering significance to comprehensively study the spatial distribution characteristics,mesostructure and mechanical properties of saline frozen soil in the Qinghai-Tibet Engineering Corridor.Based on the investigation and analysis of the saline（salinization）frozen soil in the Qinghai-Tibet Engineering Corridor,the type,degree and spatial distribution of the saline（salinization）frozen soil in the corridor are revealed.On this basis,a series of laboratory tests,such as freeze-thaw cycle,CT scan and direct shear,were carried out on silty clay,a typical saline（salinization）frozen soil in the Qinghai-Tibet Engineering Corridor.The mesostructure damage process and mechanical strength change law of the soil sample under different water content,different freeze-thaw cycle times,different salt types and different salt contents were obtained.Through the above research,the following research results are obtained:（1）The p H value of saline（salinization）frozen soil in the Qinghai-Tibet Engineering Corridor varies from 6.81 to 10.87,and the whole is weak alkaline;Among them,the cations in the salt are mainly Na⁺+K⁺,the anions are mainly Cl^-and SO₄^2-,and the ion contents are ranked as follows:SO₄^2->Cl^->Na⁺+K⁺>HCO₃^->Mg²⁺>Ca²⁺>CO₃²⁺>NH₄⁺.（2）The saline（salinization）frozen soil in the Qinghai-Tibet Engineering Corridor accounts for 54.9%,of which the saline frozen soil accounts for 11.64%,and the salt content is mainly between 0.3%and 2%.Most of them belong to weak medium saline soil and no super saline soil;The proportion of salinized frozen soil is 43.26%,which is mainly acid salt,indicating that the salinization phenomenon of permafrost in the corridor is very developed.（3）In the Qinghai-Tibet Engineering Corridor,there are five kinds of saline（salinization）frozen soil,including alkali salt,sulfate,sulfite,chloride salt and chloride salt.The shallow layer is mainly alkali salt and acid salt,and the middle and deep layer is dominated by acid salt.It shows the development characteristics of"bottom accumulation type"and"surface accumulation type"on the soil layer,and the distribution trend of"high in the north and low in the South"in the section.（4）The number of freeze-thaw cycles is positively correlated with the damage of water content to the mesostructure of saline frozen soil.With the increase of water content,freezing and thawing times,the porosity of saline（salinization）frozen soil increases,and the deformation and failure characteristics of soil structure become more obvious.（5）The influence of freeze-thaw cycle times on the shear strength of soil is as follows:with the increase of freeze-thaw cycle times,the cohesion decreases sharply until it tends to be stable,showing the characteristics of 0-6 times of sharp decrease,6-10 times of slow decrease,and 10-30 times of basically stable change;The internal friction angle increases sharply until it tends to be stable,showing the characteristics of 0-6 times of rapid increase,6-10 times of slow increase,and after 10 times,it basically tends to be stable.（6）The shear strength of different types of saline（salinization）frozen soil varies widely,where the cohesion decay is ranked as follows:sulfate>chloride>carbonate,while the internal friction angle is not significantly ranked.