:  The structural state of sewer systems is often quantified using condition classes. The classes are based on the severity of structural defects observed on individual pipes within the system. Here, a survival analysis model was developed to predict the overall structural state of a sewer network based on camera inspection data from a sample of pipes in the system. The convolution product was used to define the survival functions for cumulative staying times in each condition class. An original calibration procedure for the sewer deterioration model was developed to overcome the censored nature of data (left censored and right censored) available for the calibration of sewer deterioration models. The exponential and Weibull functions were used to represent the distribution of waiting times in each deterioration state. Cross‐validation tests showed that the Weibull function led to greater uncertainty than the exponential function for the simulated proportion of pipes that are in a deteriorated state. Using various sample sizes for model calibration, these cross‐validation tests also showed that the model's results are robust to smaller calibration sample sizes. This confirms the model's potential for predicting the overall state of deterioration of a sewer network when only a small proportion of the pipes have been inspected.

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The first objective of this paper is to demonstrate how mathematical models simulating the structural state of sewer pipes can help to assess the financial resources required for the preservation of sewer networks. The second objective is to assess and compare the annual replacement rate that should be applied to four different Canadian sewer networks to stabilize their global structural state for the long term. The required annual replacement rates are similar for the four studied networks, even if their global structural states were different prior to replacement. Results also show that the required annual replacement rate is three times less if the deterioration states of all pipes in the network are known, as opposed to the case where the structural states are unknown. This demonstrates the importance of sewer pipe inspection for the planning of sewer pipe renewal.Résumé : Le premier objectif de cet article est d'illustrer comment les modèles mathématiques simulant l'état structural des réseaux d'assainissement peuvent aider à la planification des ressources financières nécessaires pour le maintien de l'état des réseaux d'assainissement. Son second objectif est d'évaluer et de comparer le taux de remplacement annuel qui devrait être appliqué sur quatre réseaux d'assainissement canadiens, en vue de stabiliser à long terme leur état structural global. Les résultats montrent que les taux annuels de remplacement requis sont les mêmes pour les quatre réseaux à l'étude, même si leur état structural global était différent avant que le remplacement débute. De plus, le taux annuel de remplacement requis est trois fois moindre lorsque l'état structural de toutes les conduites du réseau est connu, par rapport à la situation pour laquelle l'état structural n'est connu pour aucune des conduites de ce réseau. Ceci démontre l'importance d'une bonne stratégie d'inspection des conduites d'assainissement.