Rehabilitation of sewer networks is a huge and very costly global problem that has often been treated on a crisis-based approach. The development of a rehabilitation program requires models and tools for assessing the condition and performance of sewers. The original contribution of this study is the development of a ranking scheme for sewer rehabilitation priorities. A fuzzy expert system was applied with inputs from a combined assessment of hydraulic, structural performance and potential failure consequences. The fuzzy structural system computes the global structural performance index for each pipe using internal condition, surrounding condition, and site vulnerability (SV) as inputs. The fuzzy hydraulic system uses hydraulic performance index (HPI), hydraulic performance impact, and SV to compute the global HPI. Finally, the fuzzy global system uses all these factors to compute the global performance index for each pipe. This methodology was successfully applied to the sewer system of the City of Laval in Canada. The results show how the fuzzy inference system may be used to establish rehabilitation priorities for each pipe section. The fuzzy expert system provides more realistic results than the intuitive approaches that use structural and hydraulic performance maximum and mean.

La planification de la réhabilitation des réseaux d'égouts, qui sont le siège de mises en charge, de débordements et d'inondations intempestives, est un problème complexe qui nécessite le développement d'outils qui intègrent de nombreux paramètres influençant l'état des conduites. En général, seuls les aspects structuraux sont pris en compte dans la planification de la réhabilitation des réseaux de drainage. Dans cette étude, l'intégration des deux aspects (structural et hydraulique) de performance est considérée. La méthodologie proposée sélectionne la démarche de réhabilitation adaptée à chaque tronçon afin de minimiser l'écart global par rapport aux niveaux de performance structurale et hydraulique ciblée tout en respectant un budget alloué. Le « goal programming » a été utilisé comme méthode de résolution du problème multi-objectif. La méthodologie a été testée sur le réseau du secteur 1 de Verdun, un arrondissement de Montréal. Les résultats montrent l'applicabilité de la méthodologie et son succès.Abstract: Sewer rehabilitation planning is a complex problem that needs the development of some tools that facilitate the integration of many factors and parameters influencing the status of sewer pipes. Generally only the structural aspects are considered in the rehabilitation planning and sewer degradation studies. Some studies that integrate the hydraulic performance do not consider the real responsibility of each pipe in the surcharges or they only introduce a prioritization without considering the economic factors or the suitable rehabilitation method to use. In this study, an integration of two aspects (structural and hydraulic) of the performance of sewer pipes is considered and the planning over a time horizon is presented. The proposed methodology selects the suitable rehabilitation method for each sewer pipe in order to minimize the overall deviation from the desired structural and hydraulic performance levels within a limited budget. The methodology requires, on one hand, the standard structural classification of the pipes, which is considered in the computation of the initial structural performance. On the other hand, the global hydraulic performance of each conduit is calculated by computing the runoff flows at its entry. These flows are then considered to evaluate the real capacity of the pipes as well as their corresponding performance indexes. An optimisation model is then developed in order to determine the suitable rehabilitation method for each pipe that permits to approach the desired hydraulic and structural performance of the system without exceeding the maximum budget. The methodology has been tested on a sewer of the sector 1 in Verdun, a district of Montreal. The results show the applicability of the methodology and its success.