Abstract
The direct shear tests of different dry density and moisture content samples at different temperatures of the frozen soil in the Qinghai-Tibet Railway embankment between Tanggula South and Anduo section were carried out to analyze the influence rules of each experimental factor on the mechanical properties of frozen soil during the freeze-thaw process. The results show the following. (1) When the frozen soil temperature is below 0°C and continues to drop during the freezing and thawing process, each sample shows the law of a significant increase in cohesion and a slight decrease in the internal friction angle. In the meantime, the cohesion obtained during the thawing process of the sample at the same temperature point is higher than that obtained during the freezing process. In contrast, the internal friction angles exhibit an opposite law, where the internal friction angle during the melting process is lower than the internal friction angle during the freezing process. After freezing-thawing action, it deserves to be mentioned that the cohesion increases slightly while the internal friction angles present a slight decrease trend compared to the initial state. (2) With the decrease in temperature and the gradual increase in cohesion, the temperature curve can be divided into a fast-growing section from 0 to −2°C, a slow-growing section from −2 to −8°C, and a second fast-growing section from −8 to −10°C owing to the combined effect of the pressure-thawing action and ice-water phase change. In addition, the rate of decrease in the internal friction angle also shows a similar pattern. (3) The cohesion and the internal friction angle of samples both tend to increase first and then decrease with the rise of the initial moisture content, and the critical initial moisture content is near the optimal moisture content of 15%. (4) Both the cohesion and the internal friction angle of the samples increase with dry density growth. The growth rate of cohesion will gradually increase as the temperature decreases. Moreover, the growth rate of cohesion of low dry density samples is more susceptible to temperature, while the internal friction angle growth rate is not affected by temperature.
Highlights
Permafrost is generally defined as a negative temperature or ice-bearing zero-temperature rock and soil that has been in a frozen state for more than two years [1]. e combined effects of human activities and global warming have resulted in significant degradation of permafrost areas and a continuous increase in average ground temperature worldwide [2]
(1) When the frozen soil temperature is below 0°C and continues to drop during the freezing and thawing process, each sample shows the law of a significant increase in cohesion and a slight decrease in the internal friction angle
The rate of decrease in the internal friction angle shows a similar pattern. (3) e cohesion and the internal friction angle of samples both tend to increase first and decrease with the rise of the initial moisture content, and the critical initial moisture content is near the optimal moisture content of 15%. (4) Both the cohesion and the internal friction angle of the samples increase with dry density growth. e growth rate of cohesion will gradually increase as the temperature decreases
Summary
Permafrost is generally defined as a negative temperature or ice-bearing zero-temperature rock and soil that has been in a frozen state for more than two years [1]. e combined effects of human activities and global warming have resulted in significant degradation of permafrost areas and a continuous increase in average ground temperature worldwide [2]. The main direction of current research is to focus on the influence of freezing and thawing cycles on the strength of frozen soil, while there are few studies on the evolution of frozen soil strength during the freezing and thawing process. In order to have a clearer understanding of the evolution of the mechanical properties of the QinghaiTibet Railway subgrade permafrost under the effects of freezing and thawing, direct shear tests were carried out on frozen plateau powder clay collected from the embankment of the subgrade of the Tanggula South and Anduo section of Qinghai-Tibet Railway at different initial moisture contents and dry densities under various temperatures during the freeze-thaw process. In order to have a clearer understanding of the evolution of the mechanical properties of the QinghaiTibet Railway subgrade permafrost under the effects of freezing and thawing, direct shear tests were carried out on frozen plateau powder clay collected from the embankment of the subgrade of the Tanggula South and Anduo section of Qinghai-Tibet Railway at different initial moisture contents and dry densities under various temperatures during the freeze-thaw process. e results can further supplement the research field of the impact of freezing-thawing on the mechanical properties of permafrost on the Qinghai-Tibet railway subgrade and provide a theoretical reference basis for the study of the perennial deformation of the roadbed of Qinghai-Tibet Railway and the safe operation and maintenance of Qinghai-Tibet Railway in the future
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
