| With implementation of several key projects of gas transportation and high-speed development of urbanization, polyethylene (PE) pipe has become the main choice of urban gas running piping, with its outstanding merits including corrosion resistance, long service life, cost-effectiveness, and friendly to the environment.In recent years, geological disasters occur more frequently, and illegal and savage constructions are commonly seen. Hence, buried PE pipe is confronted with quite complex geological environment, and its safety faces challenges. At present, research on strength of PE pipe is mainly focusing on hydrostatic situation, while research on mechanical performance of PE pipe under complex loading is still in its infancy. Moreover, now available results of buried steel pipe are not suitable for PE pipe. In order to improve safety of buried PE pipe, the needs are urgent for numerical simulation of strength of buried PE pipe under complex loading and laying a foundation of proposing relevant safety assessment method.Supported by National Key Technology R&D Program of P. R. China (Project No.2011BAK06B01), this thesis conducted numerical simulation of strength of buried PE pipe under two typical complex loadings-seismic landslide and tie up. The main work of this thesis is listed below:(1) Using common failure causes proposed by Plastic Pipe Database Committee of U.S.A., complex loadings were screened. Combined with the frequency, handling information and impact, two typical complex loadings of buried PE pipe were determined:seismic landslide and tie up.(2) Based on hyperbolic constitutive model proposed by Suleiman et al., using results of uniaxial tensile tests of various strain rate, the constitutive model and yield failure criterion were obtained to simulate mechanical behavior of PE pipe under specific complex loading. Numerical simulation method of buried PE pipe under complex loading was demonstrated using nonlinear finite element, including nonlinear material, geometric distortion and pipe-soil contact. Based on t failure criterion of PE pipe yielding, limit load was determined.(3) Using finite element simulation tool ABAQUS, the deformation and mechanical behavior of buried PE pipe under a seismic landslide and tie-up situation were investigated and influencing factors were taken into condsideration. From numerical results, the following conclusions are drawn:· Displacement of buried PE pipe is distributed as a quartic polynomial, and on the symmetric plane, cross-section of PE pipe deforms obviously. The maximum Mises stress increases as maximum displacement of PE pipe increases, while its location is changing from springline to sole. It is because the governing mode of failure is cross-section deformation caused by the resistance of surrounding soil in the front of the landslide. When it yields, the maximum displacement of PE pipe is rising in direct ratio to landslide width L, while the maximum pipe deflection remains almost the same δy=0.154.· Maximum displacement of PE pipe occurs on crown on the symmetric plane. Cross-section of PE pipe deforms obviously. As tie-up load increases, the location of maximum Mises stress is changing from sole (crown) to springline. When it yields, the tie-up load differs in inverse ratio to both length and width of tie-up area, while the maximum displacement of PE pipe differs in direct ratio to them; pipe deflection does not be affected by them.(4) Based on analyses of finite element simulation and combined with engineering principal of field testability, strength evalution method of buried PE pipe under certain complex loading was proposed, in order to lay a theoretical basis for safety assessment method. In seismic landslide cases, safety of buried PE pipe can be determined with relation curve of maximum offset of PE pipe and landslide width. When it comes to tie-up situation, safety of buried PE pipe can be determined using three-dimension curve surface of tie-up loading, longth and width of tie-up area. |
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