Effect of local wavy imperfections on the elastic stability of cylindrical liners subjected to external uniform pressure

In engineering practice, the majority of the damaged utility or sewage pipelines are structurally safe, but due to the strict hydraulic requirements they require lining. For pipelines below groundwater table, liners should withstand safely the external groundwater pressure. Besides, liners are expected to carry external pressure associated with pumping of the grout around the liner to fill any gaps between the liner and its host pipeline.The critical external pressure at which the liner may buckle or become unstable has been the subject of many studies. Previous research work has always focused on the effect of global imperfections (such as ovality, loose-fit and wrinkle) on the stability of liners. Meanwhile, there is a lack of information regarding the influence of three-dimensional local imperfections on the stability of liners. The current paper reports on a numerical study that investigates the effect of various geometric parameters of local wavy imperfections on the elastic buckling pressure of cylindrical liners. New formulae based on the results of the study are suggested and may contribute to the update of current design specifications of cylindrical liners. The results are expected to help researchers to design for future experimental investigations to provide more insights into stability and behavior of locally imperfect liners.