Analysis On Mechanical Characteristics Of Pipelines Buried In Soft Soil Under Transportation Loads

With the increase of urbanization process, transportation and municipal utilities have a rapid development, and the construction of pipelines becomes more and more broad. At the same time, constrained by geologic condition and engineering practice, many pipelines have been buried in soft soil. Under the loads of upside soil and vehicles, those pipelines buried in soft soil are prone to produce longitudinal bending and overlarge deformation, these two influences will cause pipelines to lose stability and to produce breaks in the weakest parts, which will lead to leakage and even blowout. These accidents will influence normal operation of national economy and peoples' daily lives, and bring serious economic and social damages. Therefore, in this paper, the mechanical characteristics of buried pipelines under transportation loads are calculated and analyzed. The main contents are as the following:1. According to the functionary times of transportation times and spatial location between pipelines and roads, three kinds of transportation load models are put forward, i.e. long-term evenly distributed load, movable invariable load and stable simple harmonic load. Two common foundation models, linear elastic model and modified Cambridge model are analyzed, and the former is selected as the model for soft soil in this paper. Considering the application actuality and foreground of steel, steel pipeline is adopted as research object. Pipeline-soil interaction model is discussed from normal and tangential directions.2. Three-dimensional calculation and analysis of Mises stress and vertical displacement of buried pipelines under three different kinds of transportation loads are carried out. When the transportation load is long-term evenly distributed, the influences of each relevant factor, i.e. pipeline depth, diameter, deformation module of foundation, Poisson ratio of soil and tyre pressure of vehicles, toward Mises stress and vertical displacement of pipelines are discussed. When the transportation load is movable and invariable, the changing rules of Mises stress and vertical displacement during the vehicle's movement are calculated and analyzed, and effects of vehicle velocity and tyre pressure toward these two mechanical characteristics are discussed. When the transportation load is stable andsimple harmonic, the changing rules of Mises stress and vertical displacement during the time of load function are calculated and analyzed, and effects of vehicle velocity and tyre pressure toward these two mechanical characteristics are also discussed.In three-dimensional analysis, Mises stress and vertical displacement of pipelines under three kinds of transportation loads are calculated, and the analysis and discussion of correlative factors are also made. The impacts of each factor toward pipelines are compared, as well as those of long-term evenly distributed load and movable invariable load.3. Planar calculation and relative analysis of vertical displacement of buried pipelines under three different kinds of transportation loads are made, which can provide certain reference to three-dimensional analysis.4. According to results of planar analysis and three-dimensional analysis, comparisons of influences between different factors, long-term evenly distributed load and movable invariable load, planar analysis and three-dimensional analysis toward pipelines are carried out respectively.5. According to the results obtained from planar and three-dimensional analyses, pipeline protection and foundation treatment measures, which can be adopted in project design and construction, are put forward.6. The method and results of this paper will provide certain theoretical method and reference for continuous research on mechanical characteristics of buried pipelines under transportation loads in future.