A study of reactive soil influence on small diameter pipe failures in Melbourne

Melbourne’s water reticulation system experiences about 4000 pipe breakages or bursts in each year, causing difficulties to both water utilities and water users. The majority of these failures are in old cast iron pipes that can be up to about 100 years old. For reticulation or small diameter cast iron pipes (diameter less than 300mm), the failures occur around the pipe circumference (known as broken back failures) mainly due to pipe bending. It is well established that the seasonal ground movement in reactive soil zones in Melbourne has a notable impact on pipe bending and resultant failures. The present study examines in detail the failure process of small diameter pipes that are affected by reactive soils. Finite element models of unsaturated soil-pipe interaction are used to simulate the response of the pipe to reactive ground movements that are governed by soil moisture variations. Locations where high pipe stresses due to ground movements are likely to occur are identified as stress “hotspots” to determine the potential for pipe failure. The concept of these stress hotspots is verified or corroborated by collecting field information from recent pipe failures in Western suburbs of Melbourne where highly/extremely reactive soils are commonly present. The results of this study are presented in the form of a simplified analytical method to estimate pipe stresses based on the soil moisture changes at the pipe level. With this development, mechanistic failure models are developed that could be implemented in a GIS platform for failure prediction and visualisation.