HDPE Coupling

The performance of a corrugated High Density Polyethylene (HDPE) pipe under high earth load was investigated. The cross-sectional shape of the pipes were essentially round after 5 years of burial. However, visual observations showed the development and growth of circumferential cracks in the unlined corrugated pipe and buckling of the unsupported portions of the liner in the smooth wall corrugated pipe. The cracks were mainly in the inside corrugation crests within the coupling length. The liner buckles were in the bottom half of the pipe. Material property tests on HDPE specimens cut from pieces of pipe showed the existence of longitudinal residual tensile stress in the pipe wall that were close to the yield stress of the HDPE. These residual stresses combined with longitudinal tensile stress induced by the coupling were probably the main cause of the crack development in the field. Laboratory tests were conducted on short lengths of pipe in ring bending and in hoop compression. The ring bending tests showed that the material modulus under short-term deflection increments does not diminish with time, whereas the apparent modulus under sustained deflection decreases with time. The hoop compression tests showed circumferential shortening, corrugation closure and liner buckling under external radial pressure consistent with the field observations.

Credit: HDPE Coupling

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