Long-Term Structural Behavior of Pipeline Rehabilitation Systems

An investigation into the long-term structural performance of pipe rehabilitation products, specifically cured-in-place pipe (CIPP) and fold-and-formed pipe (FFP), was sponsored by the joint Corps of Engineers and industry Construction Productivity Advancement Research (CPAR) program. The overall objective of the research was to evaluate the long-term structural behavior of CIPP and FFP liner products made by different manufacturers when subjected to external hydrostatic pressure. A test program was designed to simulate the sustained hydrostatic loading that would be experienced by liners constrained in partially deteriorated gravity sewer pipes. Test results indicate that the viscoelastic behavior of the plastics leads to buckling of the liners under significantly lower pressures as the load is sustained over longer periods of time. A regression analyses of the test data extrapolated beyond the 10,000-h test period, shows that the estimated long-term buckling pressure is generally greater than that currently predicted by industry participants when using the design considerations in ASTM F 1216-93. Test results suggest that additional research and evaluation may lead to more efficient designs for CIPP and FFP systems. The results of this research are expected to have a significant impact on the design and analysis of rehabilitation systems for existing pipelines.