An important step towards the assessment and management of failure risk in large-diameter (transmission) water mains is to observe distress indicators through scheduled inspections (using non-destructive or visual techniques) and translate these into condition ratings. Condition rating reflects an aggregate state of the pipe's health.

Distress indicators are physical manifestations of the ageing process. The type (or form) and location of observed distress indicators in large-diameter mains are dependent on the pipe material and its surrounding environment. The physicochemical processes that promote ageing are often not understood well enough to merit an adequate physicochemical (based on mechanics or electrochemistry or microbiology) model. Further, the encoding of distress indicators into condition rating is inherently imprecise and involves subjective judgement. Fuzzy logic-based tools enable the use of engineering judgement, experience and scarce field data to translate the level of distress to condition ratings.

This paper describes the translation of distress indicators detected by non-destructive or visual techniques into fuzzy condition ratings. Examples of distresses observed in prestressed cylinder concrete pipes (PCCP) and cast iron pipes are used to illustrate the proposed method.

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