The Experiental Analysis And Study On Thawing Settlement Characteristics Of Frozen Soil

Surface temperature has been changed, due to natural (such as climate warming) or man-made factors (such as deforestation and burning of trees, housing heating), which increase the depth of seasonal melting of underground ice and permafrost layer. Soil thawing occurred, in the soil outside of the self-determination and under pressure, a phenomenon known as thawing settlement。At the initial stage of construction in permafrost areas, if the foundation settlement caused by melting is failed to be predicted, the settlement may exceeds the allowable deformation of buildings in the operating process, which resulting in the abnormal use of the building. From experiences and lessons around the world, the most common damage of buildings and structures in frozen soil area is the drastic change because of possible subsidence and the dramatic changes while foundation melting is not unforeseen. In 1920s, about two-thirds of the global heating building built in frozen soil areas could not be used normally due to the excessive thaw-frozen settlement. As been reported in the Soviet Union in 1970s that, 80% of the 40,000 houses built in Vorkuta of the Far East suffered uneven deformation of frozen damage. Survey results obtained by yakeshi forestry survey and design institute of China in 1981 showed that, 80% of half-timbered housing of mangui tree in the northeast farm had generated crack of various degrees due to uneven settlement, and many of them had been damaged to dump, while the rejection rate of wooden structure housing was 57.3%. The disease survey of permafrost roadbed of Qinghai-Tibet Highway also showed that the thaw-frozen subsidence deformation accounted for more than 80% of roadbed frozen damage, mainly in high temperature permafrost with lots of ice.This paper is based on the Sino-Russian oil pipeline, Antarctic pole and Jilin Province highway roadbed survey of freezing damage. For the foundation soil of pipeline construction area and roadbed freezing zone, firstly used some methods such as drilling to obtain the undisturbed soil samples, then conducted a variety of physical properties test of frozen soil, and proceeded melting compression test, finally analyzed the test results by mathematical statistics. This paper is divided into six parts:1.Summarizes the concept of frozen soil, the basic physical properties, and several important factors that impacting the properties of frozen soil, furthermore discusses the purpose and significance of studying frozen soil thaw collapse, at last briefly describes the content and methods of this research;2. First of all, briefly introduces the phenomenon and mechanism of frozen soil thaw collapse, as well as hazards to civil building caused by once predicting the thaw subsidence coefficient in error. Then introduces the test principle and descript the test equipments, test steps, as well as the collation of results in detail. Finally, emphatically introduces the test apparatus, methods and steps;3. At first introduces the effect factors of thaw subsidence coefficient, and then analyzes the relationship between the thaw subsidence coefficient and the moisture content, dry density of different soil in different area by mathematical statistics, following that establishes a good correlation mathematical model. The results show that the thaw subsidence coefficient of different soil has a better linear relationship with the moisture content and dry density, and increases with the increase of moisture content increases, decreases with the increase of dry density. At last, analyzes the relationship between the thaw subsidence coefficient and moisture content, dry density by analysis software spss; and establishes a mathematical relationship equation. Through the comparison and analysis, it can be concluded that the impact of moisture content on the thaw subsidence coefficient is greater than that of dry density. 4. This part respectively introduces the norms and the empirical estimated formula of thaw subsidence coefficient of Lanzhou frozen soil institute. Then through data analysis, sums up the empirical estimated formula of this paper, and makes a comparison. The study found that whether the relationship between the thaw subsidence coefficient and moisture content or the relationship between the thaw subsidence and dry density, the thaw subsidence coefficient of this article is smaller than that of the norm.5. This part firstly introduces the method and basis for classification of frozen soil, and then introduces a standardized classification of frozen soil thaw collapse in Russia and China. Following that summarizes thaw collapse classification of frozen soil of this paper by data analysis, and compares with the norm. The analysis found that the critical moisture content in this article is bigger than that of the norm, which is a very strong supplement to the norm.6. This part is the conclusion of this paper, and it makes a summary of the data analysis studied in the previous chapters, which makes the results of this paper more clear and concise.