Development of novel methods for municipal water main infrastructure integrity management

Phan, Hieu Chi (2019) Development of novel methods for municipal water main infrastructure integrity management. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Water Distribution Network (WDN) is an important component of municipal infrastructure. Many municipal water distribution systems are exposed to harsh environment and subjected to corrosion with age. Many of the water mains in North America are close to or have exceeded their design life and are experiencing a number of issues associated with leaks and breakage of the water mains. Maintaining structural integrity of the water infrastructure with the limited municipal budget has been a challenge. Under this circumstance, the municipalities are focusing on prioritizing their infrastructure for maintenance with optimum utilization of the resources. In this regard, an effective method for prioritizing is required for optimally maintaining the infrastructure integrity. The proposed research focuses on developing risk/reliability based prioritizing methods for water main infrastructure maintenance. Historic water main break data (i.e. number of breaks per km) is often used to identify breakage patterns in the attempts to reliability assessments of deteriorating water mains. This statistical modelling approach is unable to identify the failure mechanism and have limited use. Physical/mechanistic models are therefore desired for better understanding of the failure mechanisms and reliability assessment of WDN. In the proposed research, mechanics-based model is developed for the reliability assessment of water mains. Existing models for remaining strength assessment of the deteriorating pipelines are first examined to develop improved models. Pipe stress analysis is then performed for the reliability assessment of the pipes based on a stochastic analysis using Monte Carlo simulation. For prioritizing water mains, system reliability and risk assessment methods are employed. For small WDN, the system failure of the pipeline network is modeled using Fault-Tree Analysis (FTA). The FTA is however tedious for large complex network. For large WDN, a complex network analysis method is employed to determine the potential of network disconnection due to water main break. Algebraic Connectivity (AC) of a complex network analysis is found to effectively represent the robustness and redundancy of WDN. The fluctuation in AC due to water main break could be used to assess the criticality of each pipe segment to the overall structure of the network. The AC then used as a part of overall consequence of the network due to water main breaks. A Fuzzy Inference System is proposed to combine network consequence with other consequence for risk assessment of complex WDN. In summary, a novel risk/reliability-based method for maintenance of water distribution system is developed in this thesis. In developing this method, mechanics-based failure is considered for reliability assessment and AC from graph theory is used for the consequence assessment of water main break on the overall network. A framework is developed for risk assessment considering the reliability and various consequences.

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