Determination of the optimum geofoam geometry for shallowly buried flexible pipe by finite element analyses

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2020-12-28

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Kefci, Yavuzhan

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Buried pipes are subjected to various loading conditions such as embankment loads, traffic loads etc. and in order to protect the buried pipes, the induced trench method and compressible inclusions are used. Expanded polystyrene (EPS) geofoam is one of the most advantageous compressible material that is used for protection of buried pipes. In the literature, researchers generally focused on the protection of rigid culverts and pipes, and there has been only limited amount of research on the protection of buried flexible pipes, which have limits of pipe deformation in their service life. This study aims to define the optimum EPS geometry that would be placed on top of the shallowly buried flexible pipe, via finite element method using PLAXIS 2D software. Firstly, a verification study is conducted with the results of an extensively-instrumented laboratory model test from the literature. Then, the verified numerical model is used to investigate the effects of the EPS geofoam's geometrical properties such as optimum width and thickness in addition to its location and density with more than 120 numerical analyses. Besides, in the case of using two layers of EPS, the effects of EPS layers' location and their spacing is examined with numerical analyses. For the protection of flexible pipes with the help of EPS geofoam, the varying improvement ratios (22% and 84% improvement in pipe deflection) are achieved using different density, location and geometry of the EPS geofoam. For the 30-cm pipe diameter, under uniform embankment loading conditions at the ground surface, by considering cost / performance criteria, it is recommended that (i) EPS should be located right above the pipe crown, (ii) width of EPS geofoam is suggested as 1 x diameter of pipe (D), (iii) EPS geofoam thickness is suggested as 5 cm (D/6) to mobilize the positive arching fully, (iv) more compressible EPS should be preferred (in this study EPS-10 having 10 kg/m3 nominal density) without exceeding the yield strength of the EPS. The literature review presented in this study will be an up-to-date resource for the researchers, and the results of the study will contribute to the more effective design of the protection systems of shallowly buried flexible pipes by imperfect trench method with EPS geofoam.

Subject Keywords

Shallowly Buried Flexible Pipe, Plaxis 2D, EPS Geofoam, Soil Arching, Imperfect Trench Method

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https://hdl.handle.net/11511/89576

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

Y. Kefci, “Determination of the optimum geofoam geometry for shallowly buried flexible pipe by finite element analyses,” M.S. - Master of Science, Middle East Technical University, 2020.