Numerical investigation of failure mechanisms of cast iron water mains

Hordiyamulla Liyanage, Kasuni Tharuka (2016) Numerical investigation of failure mechanisms of cast iron water mains. Masters thesis, Memorial University of Newfoundland.

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Cast Iron water mains used in potable water transportation systems are facing a rapidly growing rate of failure. The most common failure mode of cast iron water main is circumferential cracking that occurs due to high longitudinal stresses in the pipe wall, when the longitudinal stress exceeds the strength of the pipe material. However, the circumferential failure mechanism of the pipe is not well understood. Conventional methods of pipe analysis predict higher circumferential stresses, which would cause longitudinal cracking in the pipe. The higher longitudinal stress is attributed to a number of factors such as corrosion pits on pipe wall, lack of bedding support due to erosion of bedding soil, and localized concentrated supports (or forces) due to lumps of soil or rock pieces. The failure mechanisms of buried cast iron water mains subjected to three factors such as non-uniform bedding support, pitting corrosion and localized concentrated supports are investigated in this thesis. A detailed numerical investigation is carried out based on three-dimensional finite element analyses using ANSYS software. The non-uniform bedding is found to create high longitudinal stresses for larger void at the pipe invert. Although pitting corrosion alone results in high circumferential stresses, when it occurs simultaneously with a non-uniform bedding condition, the peak stresses result in the longitudinal direction. Longitudinal stress is generally higher than the circumferential stress for the pipes with higher relative stiffness with respect to soil. The presence of localized supports is found to be a critical factor, which leads the stresses to exceed the strength of the cast iron material. This study contributes to the development of a better understanding of the mechanism of cast iron water mains failure.

Item Type: Thesis (Masters)
Item ID: 12386
Additional Information: Includes bibliographical references.
Keywords: pipe-soil interaction, cast-iron pipe, water main, longitudinal stress, circumferential cracking
Department(s): Engineering and Applied Science, Faculty of
Date: October 2016
Date Type: Submission
Library of Congress Subject Heading: Cast-iron pipe--Cracking--Mathematical models; Water-pipes--Cracking--Mathematical models; Underground pipelines--Cracking--Mathematical models; Pipeline failures--Mathematical models

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