The freezing-thawing circulation was the most common security problems of buried pipeline in permafrost regions, and it could make pipeline generate additional stress. For the regional with the special structure of topographic, the freezing-thawing circulation would change the original geological characteristics, and caused geological disasters under certain conditions. The stress impact of the pipeline was studied generated by the freezing-thawing landslide because of the melting permafrost. The degree of influence of axial landslide with different displacement on the pipeline was analyzed. The simulation analysis showed that different forms of landslide generated a great impact on the pipelines; furthermore, the effects of stress on the pipeline had a greater impact by changing the location of the landslide. The influence on the pipelines generated by the freezing-thawing landslide were simulated and analyzed ,which could well reflect the changes in stress and provide a theoretical basis for building construction of buried pipelines in the permafrost regions.

In order to optimize the transportation pipeline of heavy oil and provide baseline data for the study of energysaving technology, the experimental study on the viscosity-temperature characteristics and rheological properties of heavy oil in Huanxiling was carried out. The viscosity-temperature curve and the rheological characteristic curve were drawn, the viscosity-temperature equations and the rheological equations were fitted, and the viscosity-temperature index was calculated at each temperature interval. Through the viscosity-temperature curve and rheological characteristic curve fitting, the results showed that the correlation coefficient was close to 1 which indicated a higher degree of fitting and the small error. The rheological index was less than 1, which indicated that the heavy oil used in the experiment was pseudo plastic fluid. At the test temperature of 70 ℃,the heavy oil showed Newtonian behavior.

The earth's settlement would generate additional stress on pipeline , which was common security problems of buried pipelines. Because of the force of aerial crossing pipeline structure was more complicated, therefore a finite element mechanical model of interactions between the pipeline and soil in acrossing segments of buried pipelines was established, to analysis the changes of the stress in aerial crossing pipeline structure, when aerial crossing pipeline structure used different angles. Further, based on the model, a detailed analysis of the stress changes in the pipeline was obtained, when soil settlement occurred at different locations nearby the acrossing segments. The variation was studied on the relationships of the maximum stress within the pipeline with the position of soil settlement, when the angle between the oblique pipeline of crossing structure and the horizontal direction was 50°, provide a theoretical basis for building construction of buried pipelines.

The moisture content of soil will change when the ambient temperature changes in permafrost, and by this time the internal friction angle, cohesion and severe of permafrost will change accordingly. And for slope segments of buried pipelines, the soil will produce friction on the pipeline along the slope direction with the thawing of permafrost occurrence, to make the pipeline generate the additional tensile stress. Understanding the impact of frozen soil parameters on the pipeline stress correctly was convenient to the analysis of pipeline stress, and it had practical significance for the development of scientific and effective method of preventing damage. When the frozen soil around the buried pipeline of slope section thaws, the degree of influence on pipeline stress with different soil parameter was investigated, and yields the conclusion by the numerical simulation. The results show: when thaw landslide occurs, with the increasing of soil cohesion and weight of soil, the pipeline stress increased; and with the increasing of internal friction angle, the pipeline stress decreased. Moreover, the friction angle of the frozen soil was the most sensitive to the pipeline stress, weight of soil followed, and the influence of permafrost cohesion on pipeline stress was minimal.