The Effect of Negative Pressure on a Failed 54-Inch PCCP with a Malfunctioning Valve in the Pipeline - A Case Study

Abstract

Much research has been conducted for Prestressed Concrete Cylinder Pipe (PCCP), focusing on the performance of the pipe under normal loading conditions. However, little has been done to analyze PCCP’s performance under negative pressure that could be created by malfunctioned valves during the dewatering. This paper presents the results of a case study investigating the failure causes of a 54-inch PCCP failed under negative pressure. This investigation will improve the understandings of PCCP’s performance under negative pressure and the findings of this research will help utility owners better manage their PCCP pipeline systems. A 54-inch PCCP failed when Washington Suburban Sanitary Commission (WSSC) was dewatering the pipeline which had one valve stopped working and created negative pressure. The engineers were trying to investigate the failure causes of this pipe but they were not sure if it was the negative pressure that caused the failure. Therefore, it is very important to know the influence of negative pressure on the structural safety of the pipe to identify the actual failure cause of the pipe. If the negative pressure can cause failures of PCCP, then a condition assessment program has to be developed to examine all the valves in the pipeline periodically, which will be very costly and take long time. In this paper, a finite element (FE) model is developed to simulate the structural response of PCCP to the negative pressure, considering the number and location of broken prestressing wires. In the FE model, the weight of soils and pipe is also considered. The structural details such as concrete core, steel cylinder, intact and broken prestressing wires, and coating are simulated to fully represent the structural performance of PCCP under actual loading conditions.