External loads on buried steel pipelines: 3D finite element simulation

The combined internal and external loading on a buried pipeline produces an interaction between the pipe structure and the adjacent ground that would lead to the failure or damage of the pipeline. This interaction will depend on the form of loading on the pipe, nature and condition of the surrounding soil and on the structural characteristics of the pipe. To assess the integrity of the pipelines against combined loads, it is necessary to accurately estimate different external loads that buried pipeline are subjected to, specifically dead and surface loading. Various standards exist for estimating the external dead and live loads that the buried pipelines are subjected to, such as American Lifelines Alliance (ALA) "Guidelines for the Design of Buried Pipelines", and NEN3650 "Requirements for pipeline systems". For the calculation of backfill loads, these methods are based mainly on the same theory, i.e., Marston load theory, while the calculation of live loads, such as traffic loads, is mainly based on different approaches. Depending on the design methodology selected, there is a large variation in the calculated external loads. In this paper, current design standards and empirical methods are compared to finite element analysis (FEA) simulation of buried pipes. The comparison is validated using site-measured full scale results from Transport for London (TFL). This study shows that the approach used to assess external loading is important and using empirical approaches can lead to an overconservative analysis. Using FEA to predict external loads is the most accurate way to undertake analysis due to traffic and soil loads. Although conservative, classical empirical methods will continue to be applied to the analysis of buried pipelines, much more reliable and realistic results would be obtained by using the finite element method.