Performance assessment of buried pipes: service life and pipe-soil stability over time

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Many of our buried pipes are more than 50 years old, and Canada invests $B's each year on sewer, culvert and water pipe repair. This has prompted the development of decision support systems to minimize life cycle cost. Unfortunately, most research has considered the pipe in its initial burial configuration over its service life, setting that service life by considering how the pipe alone degrades. Actual failure often involves changes in soil and pipe components and their interaction: rigid pipe (clay, concrete) generally fails when backfill erodes as water flows in through joints; thermoplastic pipe design uses 'constant stress' testing to establish material limits which ignores varying stresses, and also neglects soil deterioration; cast iron water pipes mostly experience ring fractures, not a result of internal pressure but of longitudinal bending due to frost. Better pipe service lives are needed, considering changes in the pipe and soil system and the actual mechanisms of pipe failure. The goal is to incorporate improved models of pipe failure into decision support systems being developed with collaborators for transportation and municipal engineers. Theme A (Gravity flow pipes) will study the stability of rigid pipes in eroded backfill, how different components in joint systems interact and the implications for long term performance of flexible and rigid pipes (including a study of the loads and capacity of joints supporting vertical service connections, i.e. risers), how water inflow at joints induces backfill erosion, the long term strength of thermoplastic pipes under complex stress conditions, and the long term performance of metal and concrete culverts considering construction and other effects. Theme B (Pressure pipes) will investigate water supply pipes under frost loads and the strength of deteriorated cast iron pipes. The work will involve training of six MSc and six PhD students over the five year funding period.