Element Test Study On The Freezing Deformation Characteristics Of Unsaturated Soil

Frozen soil is widely distributed in China.Because of its particularity,the construction of foundation engineering in frozen soil area will face the problems brought by frozen soil.At present,the research on saturated frozen soil is more extensive and perfect,but the engineering practice is often faced with the problem of unsaturated frozen soil,so the research on unsaturated frozen soil is very necessary,and the unsaturated soil in nature is mainly divided into two kinds,one is the artificially compacted unsaturated soil such as subgrade or earth rock dam in engineering,The second is the unsaturated soil which is recycled by drying and wetting in nature.The different ways of formation of unsaturated soil will have a great impact on the internal structure of the soil,and ultimately show a great difference in the degree of sensitivity to frost heaving.In this paper,two different sample preparation methods,prefabricated sample pressing method and saturated air drying method,are used to simulate the formation of the above two kinds of unsaturated soil.Then,the freezing deformation characteristics of unsaturated soil unit under the condition of no water supplement are studied through laboratory tests and theoretical analysis,so as to determine the main controlling factors of the freezing deformation of unsaturated soil,The relationship between freezing deformation characteristics and mechanical properties of unsaturated frozen soil is analyzed by mechanical tests.Through experimental research and theoretical analysis,the following conclusions are obtained:（1）No matter what kind of sample preparation method is adopted,the frost heaving of soil sample increases with the increase of initial saturation at a certain degree of compaction,and decreases with the increase of initial compaction at a certain degree of saturation;When the saturation is 0.5,the frost heaving rate is almost zero;The critical saturation（0.7～0.8）of frost heaving exists in the samples prepared by saturated air drying method;And silt is easier to frost heave than silty clay.;（2）For samples with the same compactness,the initial saturation has little effect on the SFCC curve.When the temperature is higher than-10℃,the unfrozen water content increases with the increase of compactness,when the temperature is lower than-10℃,the compactness has little effect on the unfrozen water content;The pore water mainly exists in the small hole（0.001～0.3μm）when the sample is prepared by pre pressing method,the frost heaving is mainly controlled by membrane water;The pore water of samples prepared by saturated air drying method mainly exists in the big hole（0.001～3μm）The frost heaving is mainly controlled by capillary water.（3）The freezing strength of unsaturated frozen soil increases with the increase of initial saturation;the freezing strength of unsaturated frozen soil with high initial saturation is mainly controlled by ice cementation,while the contribution of capillary cohesion should be considered for unsaturated frozen soil with low initial saturation.（4）The expansion caused by ice water phase transformation and ice cementation are linear with the volume ice content of the sample;based on Liu Li model,the freezing strength parameters and volume deformation parameters of Lanzhou silt are calibrated,the frozen strength parameters a₀ and a₁ and the variable parameters b₀ and b₁ of frozen body of Lanzhou Yuzhong silt are calibrated.The values of a₀ and a₁ are12.2kpa and-28.2kpa respectively; b₀ and b₁ are 0.6 and 33.8 respectively.