Contribution of cement mortar lining to structural capacity of cast iron water mains

Cast iron water mains represent a significant component of the water pipe networks in many cities across Australia. Such pipes are usually furnished with an internal cement mortar lining, mainly to act as a physical barrier to flowing liquids to reduce internal corrosion and to reduce energy losses. Although the lining is not intended to resist internal and external loadings to the pipe, recent observations of corroded cast iron water mains showed that the cement lining can withstand some internal water pressure on its own. This reveals that the lining may contribute to the structural capacity of deteriorated pipes, although the level of this contribu- tion is unknown. This paper investigates the likely contribution of cement lining to the structural capacity of deteriorated pipes. This research is undertaken through numerical modeling of pipe-liner- soil interactions. The properties of cement linings were obtained by testing actual specimens obtained from field pipes and casting simulated lining specimens of cement-sand mixtures. The study revealed that, depending on the level of pipe corrosion, cement lining can reduce pipe stress by as much as 5 to 12% or 10 to 25% if the lining tensile strength is 1 or 4 MPa (145 or 580 psi), respectively.