Scaling of buried pipe response in sand to surface loads

Abstract

The extent to which pipelines are stressed or damaged when heavy equipment such as bulldozers, excavators, or backhoes traverse or run parallel to the backfilled ditch of the pipeline right of way is not well known. Full-scale studies of buried pipes are expensive and time consuming. Finite element analysis, numerical and analytical studies have uncertainties due to generalized assumptions. Three test programs were carried out at the C-CORE Geotechnical Centrifuge Center in an attempt to validate the centrifuge as an effective tool to model the mechanical response of buried pipes to surface loads. In the first program, twenty four surface loading tests were carried out on an aluminum model pipe in the centrifuge. The second program included three tests at full-scale, varying the soil cover on a steel pipe. For direct comparison to the full-scale tests, a third program consisted of applying surface loads to six model steel pipes in the centrifuge. In a test bed of silica sand, cover depths, internal pressures, soil density and loading position were among the parameters varied. The model and full-scale pipes were instrumented with strain gages and ovalization transducers. Comparisons of the test data from each program validate the centrifuge as an effective and accurate tool to study the response of a buried pipe to surface loading. The test program also highlighted several common characteristics of the pipe response. The main modes of pipe deformation identified under surface loading were ovalization of the pipe cross-section and bending in the long section. The ovalization mode was not associated with the traditional elliptical pipe shape, but was characterized by the pipe crown deflecting significantly with smaller deformations of the pipe haunch. The second mode demonstrated the axial strain response was dominated by longitudinal deformation at the pipeline crown (local bending) with a limited axial strain response to load at the pipeline invert (limited global bending).