Evaluation of the properties of Toronto iron water mains and surrounding soil

Abstract

The problem of ageing water pipes manifesting leaks and breaks is common to municipalities throughout Canada, North America, and the world. Among them, the City of Toronto has been confronted with water main infrastructure problems, currently encountering a break rate of roughly two occurrences per week over a network of 5347 km. The appropriate corrective action, which aims to restore pipe integrity and prevent future breaks and leaks, should be decided based on a general knowledge of the state of deterioration of the water main network, a thorough understanding of the governing failure modes, and a clear identification of the problem areas. To achieve these goals, an extensive sampling and testing programme was undertaken by the University of Toronto in collaboration with the City of Toronto. The programme encompassed a period of three years, from 1998 to 2000, and involved the testing and analysis of 100 exhumed pipe samples, mostly cast iron, in the University's structural testing laboratories. The purpose of these tests was to ascertain the extent of material loss due to corrosion, the mechanical properties of the pipe material, and the mode of failure. Simultaneously, soil samples were extracted in the proximity of the sampled pipes, identified, and classified, and their corrosion aggressiveness was investigated through tests in the University's environmental and geotechnical engineering laboratories. The outcome of this interdisciplinary investigation, complemented by further research efforts, should lead to a clearer understanding of water main failure phenomena and contribute to the efforts of the many cities endeavouring to minimize the number of break occurrences and prioritize their maintenance and rehabilitation schedules.Key words: water mains, pipes, infrastructure, cast iron, ductile iron, corrosion, mechanical properties, soil properties, site sampling.