OPTIMIZATION OF WATER SUPPLY PIPE REPLACEMENT PLANNING TO MINIMIZE LIFE CYCLE COST INCLUDING SEISMIC RISK ―A PROPOSAL FOR AN EVALUATION METHOD USING MULTI-EVENT MODEL―

Abstract

 Various Life Cycle Cost (LCC) -based pipe replacement models have been developed to more effectively replace deteriorating water supply pipes under limited financial resources. However, seismic risk, an important aspect of water supply management, has not been included in LCC because of the complex stochastic process involved. This study proposes a monetization method of seismic risk as an expected value by using the multi-event model (a type of Probabilistic Seismic Hazard Assessment often used in Japan) to examine a list of possible earthquakes from the earthquake catalog developed by Japan’s government, and give occurrence probabilities for each earthquake. Applying this method to a virtualized water supply system in seismically active area showed that inclusion of seismic risk factors hastened the replacement timing of non-seismic-resistant pipes by five to fifteen years. The study also demonstrated significant seismic risk reduction by replacing Cast Iron Pipes (CIPs), which are especially outdated and vulnerable. Thus, immediately replacing CIPs may yield substantial LCC reduction as well as seismic risk.