In laboratory testing of full-sized pipe subjected to combined axial load, internal pressure and bending, the normal failure mode consists of local buckling on the side of the maximum compressive fiber. If loading is continued beyond the initiation of buckling, and if the pipe is pressurized internally, the pipe retains its integrity while it develops a wrinkle in which very large deformations occur. Buried pipelines should behave in the same way. The paper presents the analyses carried out to assist in the interpretation of Geopig field evidence that, in September of 1997, a wrinkle existed on Slope 92 on the Norman-Wells Pipeline.

A finite element analysis of a shell model of a segment of the pipe confirmed that the wrinkle should exist. A subsequent pipe dig uncovered the wrinkle which had a configuration remarkably similar to those observed in the laboratory and to the form predicted by the analysis. Supplementary geotechnical investigations, a review of operational procedures on the line, and additional testing to determine strains within wrinkles, are presented in companion papers elsewhere in this conference. These combined papers provide a thorough documentation relative to this most interesting case history.

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