Design equations have been developed to predict the pre-yield deflections, stresses, and strains in buried flexible plastic pipes over time. The solutions consider the effects of creep in the pipe material and the surrounding soil and backfill, the water table, arching, and variable bedding conditions. These equations are obtained by regression analysis, and results are generated using a finite element program. The design equations predict pipe deflections that are consistent with those obtained in the field over a period of time. It is shown that the arching of soil surrounding a pipe can be quantified to further appreciate its cause and effects. The ratio of the pipe's vertical deflection to its horizontal deflection is shown to be an ambiguous way of defining the structural integrity of nonrigid pipes. Strain level may be a better indicator of the structural integrity of the pipe than pipe deflection, because it considers both the bending moments and the thrust in the pipe wall and can be measured against the allowable strain for that particular pipe material. Vertical pipe deflections predicted by the design equations for different depths of cover as well as for different time periods are shown tomatch field measurements well. This paper appears in transportationresearch record no. 1315, Culverts and pipelines: design, monitoring, evaluation, and repair 1991.
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