Assessing the Fracture Risk of Corroded Cast-Iron Pipes in Expansive Soils

Abstract

It is estimated that 82% of the cast-iron pipe stock in North American water distribution systems have outlived their useful service life. Previous studies have shown that moisture-induced soil expansion is a dominant failure mechanism in pipe stock buried in expansive soils; however, this risk has not yet been quantified formally. The purpose of this paper is to quantify the risk of fracture of cast-iron pipes subjected to moisture-induced soil loading. A recently developed mechanics-based pipe–soil interaction model and fracture mechanics with corrosion degradation are used to set up the reliability analysis. Monte Carlo simulation is implemented to synthesize various uncertainties into a probabilistic estimate of the failure of a pipe segment defined by its configurational parameters and age. It is observed that smaller-diameter pit-cast pipes are most at risk, and factors other than age may have a significant impact on pipe failure. The most influential input parameters are identified through a sensitivity analysis, and it is found that the contributions of corrosion parameters and soil expansion parameters to the failure probability are most significant. Limitations of the proposed framework and the areas where more research is needed are discussed in the end.