Freeze-thaw Effect Of Closed System Of Unsaturated Compacted Concentric Loess

Tongxin County is located in the south-central part of Ningxia Hui Autonomous Region.It is located in the land of Ordos and the northern part of the Loess Plateau.The latitude is 36°58’48" and the longitude is 105°54’24".It is a typical temperate continental climate with distinct seasons.The sun is strong,the temperature difference between day and night is large,the annual average precipitation is about 259mm,and the evaporation is as high as 2325mm.The anmual mininum temperature is-28.3OC,the soil has a large frost heaving,the state advocates the western development strategy,the construction of the northwest region faces construction problems,and the freezing and thawing effect has obvious regional characteristics.The freeze-thaw is improved on the concentric compacted loess through practical problems.The impact of reducing the freeze-thaw hazard,based on the research done by the previous research team,on the basis of doing some aspects that are not involved,so as to comprehensively evaluate the harm of the freeze-thaw cycle to the concentric compacted loess.The freeze-thaw test method of closed system was adopted,and the surrounding and bottom were wrapped with thermal insulation material.The freeze-thaw deformation and compression of concentric unsaturated compacted loess were studied by different degrees of saturation,conpaction and freeze-thaw cycles.Effects of collapsibility and shear strength.Analysis of the law of its effects has important guiding significance for the evaluation and prevention of freezing damage in concentric areas:(1)Under the non-hvdration condition of the closed system,the freeze-thaw deformation of concentric compacted loess is greatly affected by the freeze-thaw cycle,and the greater the saturation.the more obvious the impact;when the saturation is<40%,the sample shows the shrinkage and swelling.Phenomenon,and the greater the compaction degree,the more obvious the shrinkage and swell;the frost heaving rate and the thawing coefficient decrease with the increase of compaction degree,and increase nonlinearjy with the increase of saturation;compactness and The effect of saturation on freeze-thaw deformation is very significant,especially the effect of saturation,the saturation increases from 40%to 85%,and the maximum increase in frost heave rate is about 5%;(2)The multiple freeze-thaw cycles increase the compressibility of the loess,and the compressibility increases with the number of freeze-thaw cycles.The compaction degree and saturation have a significant effect on the compression deformation of compacted loess.The effect of conpaction on the compression coefficient is less than the effect of saturation on the compression coefficient.The increase in compression factor after freeze-thaw stability is related to saturation and compaction.(3)After repeated freeze-thaw cycles,the strength of loess becomes smaller,and the degree of compaction and saturation are the main factors.Samples with large compaction and small saturation are transformed into brittle fractures,samples with small compaction and high saturation.It is characterized by plastic failure.After 12 freeze-thaw cycles,the cohesion and internal friction angle of loess are reduced.When the compaction is constant,the saturation is larger,and the cohesion and internal friction angle are smaller.Saturation phase At the same time,the greater the degree of compaction,the greater the cohesion and internal friction angle,and the moisture content of the loess after repeated freeze-thaw will lose 1.8%.After 12 freeze-thaw cycles,the cohesion reduction decreases to a maximum of 21 and the internal friction angle decreases by about 2.1.(4)Unsaturated concentric compacted loess freeze-thaw,with the increase of the number of freeze-thaw cycles,the collapsibility increases.The maximum collapsibility coefficient can reach 0.014.The greater the compaction degree,the smaller the collapsibility of the sample.As the number of freeze-thaw cycles increases,when the degree of compaction is the same,the sample with a low water content has a large collapse deformation,and the sample with a high water content has a small deformation.The variation of the collapsibility coefficient under low pressure is greater than that under high pressure.The value of loess after compaction is less than 0.015,it can be considered that there is no collapsibility,and the freezing damage of freezing and thawing to the project can be reduced according to the control compaction degree.