Liner buckling in profiled polyethylene pipes

Thermoplastic pipes are often manufactured with profiled walls to maximize the flexural stiffness of the pipe for a given amount of polymer. Thin elements in the profile can buckle under the influence of large earth pressures associated with deep burial or other extreme loading conditions. Earth load tests have been conducted on high density polyethylene pipes with a number of different wall profiles. Two high-pressure pipe test cells have been used to conduct these tests. Observations of local buckling in the internal liners of these products have been examined and compared to stability assessments based on the conventional equation for buckling in stiffened plate structures (following modification of that equation to an equation that defines critical strain instead of critical stress). The strain levels that develop in the liner are, however, dependent on three-dimensional bending within the pipe profile. Provided the effects of three-dimensional bending in the pipe profile are considered, the modified Bryan equation appears to be a useful tool for quantifying liner stability and should be considered for inclusion in limit-state design procedures for these structures.