The Research On Frozen Ground Thawing Settlement Characteristics And Engineering Measures At Mohe-tahe Section Of Sino-Russian Oil Pipeline Project

Frozen ground areas are in the surface soil temperature below 0℃, and the region soil contains ice crystals.In these areas there is a surface layer of winter-frozen summer-melted of the freeze-thaw, property changes of the soil directly impact on the upper structure or buildings.As the temperature rises, the frozen ground comes to thaw, with the melting of ice penetrated soil into a settlement.Thawing settlement caused the damage to the buildings, which is one main reason of buildings'destruction in the permafrost region.With China's rapid economic development, more and more projects start in wider distribution of permafrost in the size of Xing'anling Mountains, the Qinghai-Tibet Plateau and the western mountainous regions. Therefore, the research on characteristics of the thawing settlement and the thawing settlement control measures is of great practical significance.This paper is based on the Sino-Russian oil pipeline project.Da Xing'anling Mountains along the pipeline in the permafrost is dissipating, the safety of the pipeline project faces a serious threat. Therefore, the thawing settlement parameter from the test, conduct in-depth studies of the thawing settlement at typical section, and corresponding measures in accordance with the characteristics of different sections provide the reference for design and construction of the pipeline project.The overall paper is divided into seven parts.The first part introduces the purpose and significance of this research, as well as thawing settlement characteristics and engineering measures on present status of study,and makes the research ideas as following:This paper takes thawing settlement laboratory research on the properties combining with typical regional engineering geological characteristics in field, and puts forward the engineering measures in accordance with thawing settlement properties at different sections.The second part makes a comprehensive presentation of the regional natural geographical and geological conditions of Mohe - tahe section of the Sino-Russian oil pipeline,and takes an evaluation to the regional engineering geological and hydrogeological conditions on the two zoning types island permafrost zone and seasonal permafrost zone. The third part analyzes laboratory research and results of soil samples thawing settlement characteristics at Mohe– tahe section.First of all, it introduces thawing settlement mechanism and thawing settlement characteristics index of frozen soil, as well as test instruments, methods and steps.And then, it takes a statistic analysis on test data. According to the previous experience, the relations of thawing settlement coefficient to water content, dry density and (W ? WP)are statistically discussed.Through the discussion, it come to the conclusion that the relation between thawing settlement coefficient and water content is approximately linear,namely thawing settlement coefficient's increase along with the water content's; a0 andγdare fitted for a good logistic relationship, namely increase of a0 along with the increasing ofγd; The quantitative relationship between a 0 and over-plastic limit water content is good, as a 0 and ( W ? WP)are fitted for a good linear relationship, namely increase of a0 along with the increase of(W ? WP). The dependence and significance of a 0 and (W ? WP) are better than that of a 0 and W ,so as for the cohesive soil, when calculating the thawing settlement coefficient, the relation between a0 and (W ? WP) is reliable.The fourth part is the engineering-geological zoning at Mohe -tahe section. According to the zoning principle of permafrost, the permafrost along the pipeline's route is divided into 26 regional segments. In addition, the distribution of seasonal frozen soil is also introduced.The fifth part takes a research on the typical region of thawing settlement property. Firstly, according to the topography and relief, the permafrost is classified as four typical areas;Secondly, it analyzes engineering geological features at representative sections of the four selected areas for understanding concrete engineering geological conditions;Again, it makes the calculations of each layer's soil based on the thawing settlement coefficient and the regression equation of permafrost water content in the third part, and takes an evaluation to thawing settlement gradation and type;Finally, the total settlement is predicted at each representative sections.The sixth part brings forward corresponding engineering measures to typical areas which is limited to the laying of pipelines in the ground.The four typical areas are treated in different measures at a integrated consider of topography and relief, the geological features of the soil and thawing settlement characteristics.Moreover, in terms of controlling of unidentified pingo and ice cone in the wild this paper also makes a corresponding engineering measure.The seventh part is the overall conclusion. Through the analysis in the six above parts, this paper makes a conclusion on thawing settlement characteristics and corresponding engineering measures, and provides the valuable reference to design and construction of Sino-Russian Oil pipeline project, additionally for the research in future.