Buckling behavior of Formed-in-Place-Pipe (FIPP) liners under groundwater pressure: An experimental investigation for buried municipal pipelines

[Display omitted] •The use of Formed-in-place pipe (FIPP) for rehabilitating drainage pipes was investigated.•Two full-scale laboratory tests were conducted to examine FIPP liner buckling behavior.•Results showed that current theory may not predict new material liner designs accurately.•Correct construction parameters ensure superior FIPP liners for various pipe cross-section. Specifications and models for FIPP lining structures are conservative, with the El-Sawy model providing the most accurate prediction of critical buckling pressure. Initial elliptical defects significantly reduce the liner's resistance to external groundwater pressure, and these defects, along with pipeline constraints, influence the deformation processes. This study emphasizes the necessity of strict quality control measures, the consideration of initial ovality during design, and the exploration of reinforcement strategies for FIPP liners. Future research should investigate the long-term creep properties of the material, assess the impact of various types and sizes of initial defects, and develop effective reinforcement technologies for FIPP liners to advance pipeline rehabilitation technologies and practices.