Selective inspection planning with ageing forecast for sewer types

TLDR

Sewer rehabilitation investments must be based on inspection and evaluation of sewer conditions relative to damage severity and environmental risks. The paper addresses forecasting sewer conditions from a limited inspected sample and proposes a procedure for scheduling inspection dates for both inspected and uninspected sewers. The authors derive empirically calibrated transition functions between condition classes from a small inspected sample, calibrate them for different sewer types, and use them—along with sewer characteristics—to forecast the most probable date of entering a critical condition class and to schedule inspection dates. The method estimates the current condition of the Dresden sewer network and projects its deterioration if no action is taken.

Abstract

Investments in sewer rehabilitation must be based on inspection and evaluation of sewer conditions with respect to the severity of sewer damage and to environmental risks. This paper deals with the problems of forecasting the condition of sewers in a network from a small sample of inspected sewers. Transition functions from one into the next poorer condition class, which were empirically derived from this sample, are used to forecast the condition of sewers. By the same procedure, transition functions were subsequently calibrated for sub-samples of different types of sewers. With these transition functions, the most probable date of entering a critical condition class can be forecast from sewer characteristics, such as material, period of construction, location, use for waste and/or storm water, profile, diameter and gradient. Results are shown for the estimates about the actual condition of the Dresden sewer network and its deterioration in case of doing nothing about it. A procedure is proposed for scheduling the inspection dates for sewers which have not yet been inspected and for those which have been inspected before.