Date

2017

Author

Söylemez, Berkan

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Buried pipelines have become one of the most common, economical and safe means of conveying fluids (water, gas, petroleum, etc..) from a region to another ranging from very small (hundreds of meters) to large distances (thousands of kilometers). These pipes may be damaged and deform due to the application of different kinds of loading such as traffic loads, heavy static loads, sloping ground, etc. Such unwanted scenarios can be avoided by using geofoams in the flexible buried pipeline projects. In this study, the effect of geofoam for the improvement of a buried flexible pipe is investigated in laboratory physical model tests. The laboratory experiments are conducted in a box having 1 m x 1 m area and 0.6 m height, where a clean sand is used as the bedding and surrounding material. A 20-cm-diameter PVC pipe is positioned on the bedding soil layer, over which EPS geofoam having different densities and dimensions are placed. Incremental static loading is applied to the ground surface via a circular steel plate (such as in a plate load test) and deformations of the pipe, as well as that of the ground surface, are measured. Introduction of geofoam above the pipe creates a compressible layer, which results in soil arching. This action reduces the loads by transferring some portion of the weight of the soil prism above the pipe to the side soil and leads to smaller deformations of the pipe cross-section. By applying different geofoams, the improvement effect –if any- was compared in terms of thickness, width and density of the geofoam panels. Moreover, the location of the geofoam relative to the pipe crown was also part of the study and related experiments were conducted. For two-layer geofoam applications, the effect of geofoam layer spacing on the pipe deformation behavior is also studied. In all of the experiments, the change in the compressible zone above the pipe and arching effect is investigated. The benefit of using geofoam is demonstrated by comparing subgrade modulus values for the cases of pipe with or without geofoam. It is found that, in nearly all experiments where geofoam was used, until the geofoam yields, it improved the pipe deformation under static loading. However, it is also seen that once the geofoam fails at large vertical deformations, they worsen the system significantly, when compared with the experiments in which geofoam was not used. It can be concluded that the benefit of using geofoam over pipes depends on the magnitude of the applied vertical stresses, in relation to the geofoam compression failure stress. This study aims to contribute to a greater understanding of the benefit and efficiency of geofoam usage and the importance of geofoam characteristics for the flexible PVC buried pipeline projects under static loads, ultimately to aid the efficient design of such systems. 

Subject Keywords

Underground pipelines., Foamed materials.

URI

http://etd.lib.metu.edu.tr/upload/12621440/index.pdf
https://hdl.handle.net/11511/26809

Collections

Graduate School of Natural and Applied Sciences, Thesis