Stresses in cast iron water mains subjected to non-uniform bedding and localised concentrated forces

A number of water main breaks occur every year in municipalities due to ageing, aggressive environmental conditions and undesirable soil conditions. However, the failure mechanism observed in cast iron water mains is often obscure. Non-uniform soil support conditions resulting from the erosion of the surrounding soil by the water escaping from leaks may induce excessive stresses on the pipe wall. Due to partial erosion of backfill soil or the presence of large rock pieces, the localised point supports on the pipe accentuate the pipe wall stresses further. This research employs three-dimensional finite-element analysis to investigate the effects of non-uniform soil support and the localised point support on the pipe wall stresses. This study results in the development of a better understanding of the mechanism of cast iron water main failure. It is shown that a localised support with a stiffness equivalent to the spring constant of 1500 N/mm may result in the failure of cast iron water mains.

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