A study of the failure of buried reticulation pipes in reactive soils

The failure of buried reticulation pipes has been reported to peak during winter months in a number of countries, including Canada and the United Kingdom, prompting much research. In Australia, the number of pipe failures has been reported to peak during summer. However, this peak does not occur in a consistent manner, varying in magnitude to such a degree as to be strongly evident in some years and scarcely observable in others. No quantitative explanation of the cause of such variation has, as yet been published. Consequently, little is known about the specific causes of seasonal failures in the Australian context. This thesis investigates the causes of the seasonal variations in the failure of Australian water reticulation pipes. An exploratory statistical analysis of historical data was undertaken and used as the basis to develop the hypothesis that the seasonal variation in pipe failure numbers in Melbourne, Australia occurs as the result of soil shrinkage. A detailed field study was then undertaken on an in-service pipe and its surrounding environment to test this hypothesis. Analysis of the data collected during the field study supported this hypothesis. A model to represent the mechanism by which soil shrinkage results in the development of pipe flexural stress is also presented. This model enables the knowledge gained from the field study to be generalised and applied elsewhere. The model uses a novel constitutive surface to determine soil stiffness and hydric expansion coefficient, and a numerical sub-model to determine the equilibrium state of the pipe-soil system. Validation of the model against data collected during the field study showed good agreement. This thesis has improved the understanding of the causes of the failure of buried water reticulation pipe, specifically focusing on the interrelated factors causing the seasonal variation of buried water reticulation pipe failures. This improved understanding will assist asset managers by enabling them to identify assets at high risk of failure due to environmental and climatic conditions.