Buried Corrugated Thermoplastic Pipe: Simulation and Design

The objective of this study was to demonstrate a computational method for assessing the allowable depth of fill over a buried thermoplastic profile wall (corrugated) plastic pipe and to compare the results with those of the recently adopted AASHTO design method. The computational method is demonstrated for a 1,500-mm (60-in.) diameter high-density polyethylene profile wall pipe but is applicable to all profile wall thermoplastic pipe that exhibits local buckling limit states. The computational model compares strain demands predicted from a two-dimensional plane strain finite element model of buried pipe in the embankment condition with strain capacity predicted from a three-dimensional finite element model of a pipe–soil segment undergoing thrust or positive and negative bending, or both. The strain demands indicate the dominance of thrust strains as opposed to bending strains in the overall behavior, particularly for intermediate to larger fill depths. In the examined profile the ultimate strain capacity is limited by local buckling for thrust strains and positive bending (crest in compression) and inward radial movement of the crest for negative bending (liner in compression). Predictions for depth of fill by the new AASHTO design method for thermoplastic pipe and the computational method agree within 10% of one another when uniform soil distribution is considered and within 20% of one another when a soft haunch and other soft soils are considered in the pipe–soil envelope.