Large-Diameter Buried Pipe-Valve System: Case Study of IPL Project and Finite Element Analysis

Operability of buried butterfly valves has been the concern of design engineers, water utilities, and manufacturers due to the complex behavior of pipe-valve as a unit system. Moreover, deflection control and stress limits are typically considered in designing buried pipes and valves. When the pipe deflects to the allowable limit (2% to 5%), the buried valve cannot operate normally, and binding and sealing issues may be observed. However, prediction of the pipe/valve deflection not only depends on the pipe/valve stiffness but also on other factors such as backfill material type and strength, location, and dimensions of reinforcing parts (butt strap and stiffening ring). To this end, nonlinear finite element analyses (FEA) of a case study from the IPL project of Tarrant Regional Water District (TRWD) were carried out to study the behavior of a large diameter buried pipe-valve system, and to investigate the effects of different pipe-valve system properties and dimensions. The aim of this study is to clarify some of the concerns in the industry regarding the operability of large diameter buried butterfly valves and provide recommendations based on the results of the current FEA. The article presents a summary of the key findings for consideration when designing a large-diameter buried pipe-valve system.