Statistical Life Data Analysis of Sewers and Prediction of Future Rehabilitation Needs

Abstract

The number of useful life years is fundamental and essential in asset management analysis but that of sewers has not been calculated statistically by using sufficient field data because most of sewers in Japan were constructed after 1960s and therefore old ones are not so many.
In this paper, a probability distribution for sewer life is presented using Weibull distribution. Future rehabilitation needs is predicted using the probability distribution.
First, the probability distribution is calculated using the life data in FY 2005. The data was obtained by a questionnaire survey for the entire sewers in Japan. The results show that actual average sewer life varies from 83 to 93 years by the applying way to all Japan data.
Next, using the Weibull distribution of 93 years, the national rehabilitation needs is estimated to peak at 4, 653 km in 2093. The rehabilitation peak is found out to be much gentler than the initial investment peak. After the peak time, the needs continue at nearly 4, 000 km per year constantly.
As readers can trace the calculating process in this paper, it is minutely explained and all Japan data are attached as an appendix.