Pipeline crossing structure was very easy to be affected by the settlement of soil along the river, and effective preventive measures should be adopted to effectively prevent the damage to the crossing structure. The finite element model of pipeline crossing structure and soil interaction was established, and the stress change of pipeline span structure with the fixed bracket was established. It was found that the fixed bracket could effectively reduce the stress value of the pipeline when the span structure was affected by the settlement of soil mass, and the installation position of the fixing bracket was more prominent to reduce the stress value of the pipeline span structure. The results could provide a theoretical basis for the safety construction of pipeline crossing structure.

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.

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.

Because of the complex terrain in the construction of longdistance buried pipeline, the elbows are widely used in pipeline systems. Due to its specificity in terms of shape and structure, elbows not only can change the axial direction of the pipeline, but also increase the flexibility of the pipeline. However, under the special conditions of environment, bends in the piping system are often the section of concentration of stress. In the certain conditions, plastic deformation occurs at the elbow, which poses a potential threat to the safe operation of pipelines. Through the application of software of finite element analysis, stress at a particular point (elbow) of buried pipeline were numerically calculated and analyzed. By numerical calculation and analysis, when the local pipeline under pressure in the radial direction, the distribution of values of Von Mises stress were obtained at the elbow, in the crossing segment of the buried pipeline. And when the length of the applied load, the bending angle and the radius of curvature of elbow were changed, the influence of the stress of the elbow was also obtained.

In reference to previous research, the simulation software to simulate overhead gas pipeline leakage diffusion in the flat areas was used and the effects of four different leakage directions and speed on leakage diffusion process were analyzed.The results showed that the risky range of upwind area was bigger than the downwind area near the ground, the higher ground was relatively safe.The risky range of upward natural gas jet was the smallest,the risky ranges of windward and downward jet were the greatest.The impact of wind speed on the risky range of windward jet was less than downward jet.Natural gas leakage in the condition of lower wind speed and calm wind spread wider.The results could be used for the emergency evacuation and rescue of overhead natural gas pipeline leakage in the future.