Baseline data on buried thermoplastic pipe behavior under biaxial loading have been developed in a controlled laboratory environment. Deflections and local wall strains of a lined corrugated high-density polyethylene pipe were determined. Use of the finite element method and simplified design equations was then evaluated relative to the laboratory measurements. Measurements of soil response during the tests were used to evaluate the constitutive response for the soil. The comparisons reveal that the two-dimensional finite element method can effectively be used to predict pipe deflections and circumferential strains in the corrugation, given that appropriate material parameters are used. Liner strains, however, are influenced by local bending, so that three-dimensional analysis is required. The simplified design methods were shown to be effective tools for pipe design. A strain factor of three in the semiempirical equation for circumferential bending strain appears to be reasonable for pipes buried in uniform ground. The finite element method was then used to study lined corrugated pipe response when the zones of backfill placed beneath the haunches have low density and modulus. These alter the location of the peak strains, may significantly increase the magnitude of the circumferential strains and the strain factor, and induce yield at the extreme fibers.
Abstract