Graduation Semester and Year
Fall 2025
Language
English
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Civil Engineering
Department
Civil Engineering
First Advisor
Himan Hojat Jalali
Second Advisor
Ali Abolmaali
Third Advisor
Xinbao Yu
Fourth Advisor
Juan Balderrama
Fifth Advisor
Amir Ameri
Abstract
The long-term performance of buried polypropylene (PP) pipes, as part of the latest thermoplastic pipe systems, has been a significant reliability concern for researchers and utility authorities due to a lack of rigorous studies and testing. The time-dependent material properties significantly affect the long-term performance of these pipes. The main goal of this research was to gain an in-depth understanding of the behavior of buried PP pipes. This study examines the mechanical behavior and properties of a 36-inch diameter double-wall PP pipe using experimental testing and nonlinear finite element analysis (FEA). The pipes were evaluated according to the relevant ASTM and AASHTO standards. Tensile and flexural creep tests were conducted in compliance with ASTM D2990-09 for a duration of 1000 hours. Coupons for tensile test were prepared following ASTM D638 from the inner wall of double-wall pipes. Also, parallel plate tests were performed on three 42-inch-long pipe samples according to ASTM D2412-11 and AASHTO M330-13 to assess stiffness and load-deflection characteristics. To better understand the creep response of these new pipes, three-dimensional nonlinear FEA of all three experiment types was carried out, and numerical results were compared with experimental data. Also, a three-dimensional nonlinear FEA framework was developed to characterize and simulate the viscoelastic response of PP using Prony-series parameters. The calibrated material model successfully reproduced both the short-term parallel plate behavior and the long-term tensile and flexural creep response, showing strong agreement with experimental measurements in all cases. All the results confirmed that the time-dependent deformation and stress relaxation of PP can be effectively represented using Prony-series coefficients, offering an efficient and practical approach for modeling PP pipes. Additionally, FE model of PP pipe buried under soil was developed using the investigated material model. Short-term and long-term deflections of the buried PP pipes for various depths of cover were determined. The long-term deflections of the buried PP pipes for various depths of cover were compared with AASHTO design method. Finally, the effects of various trench width ratios and increase in diameter of the pipe on the long-term deflections of the buried PP pipes were investigated. Results showed that both the depth of cover and exposure to loading time significantly influenced the deflections of the buried PP pipes. For every depth of cover, AASHTO design method consistently predicted higher deflection compared to FEA method, which suggested that AASHTO is more conservative in estimating long-term deflection of buried PP pipes. However, as the depth of cover increased, the difference between AASHTO and FEA predictions for long-term deflection of buried PP pipes became narrower. Also, the long-term deflections of buried PP pipes increased with the increase in trench width ratios and diameter of the pipe. This research will help build comprehensive FEA expertise within the pipe industry and promote the adoption of FEA as a standard practice in designing PP pipes, ultimately supporting potential revisions to current design methodologies. It will make a significant contribution to the existing knowledge on the material behavior and modeling of PP, while also improving the understanding of the long-term structural behavior and performance of buried PP pipes.
Keywords
Polypropylene pipes, Creep behavior, Finite element analysis, Viscoelastic material, Prony series, Buried pipe performance, Long-term performance, Thermoplastic pipes, Profiled wall pipes, Polypropylene pipe design
Disciplines
Civil and Environmental Engineering | Civil Engineering | Structural Engineering
License
This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.
Recommended Citation
Haque, Farzia, "Long-Term Performance Assessment of Buried Profiled Polypropylene Pipes" (2025). Civil Engineering Dissertations. 533.
https://mavmatrix.uta.edu/civilengineering_dissertations/533