Modeling of Pipe-Soil Interaction and Its Application in Numerical Simulation

This paper presents three plasticity models that can be applied to numerically simulate pipe-soil interaction. They can be applied individually to evaluate the force-displacement response of a small plane-strain pipe section or in combination to simulate a long pipeline system. In the latter, numerous pipe-soil elements are attached to structural finite elements, each simulating localized foundation restraint along the pipeline. The three models are increasing in sophistication, mainly due to the manner in which they account for the behavior within an allowable combined loading surface. The first is based on traditional strain-hardening plasticity theory and therefore assumes a purely elastic response inside a single expandable yield surface. The second allows some plasticity due to the use of a bounding surface, and the third accounts for kinematic hardening through the introduction of a second smaller surface. The models are detailed in this paper, allowing for simple numerical implementation. Importantly, they are incorporated within the structural analysis of a pipeline and their potential to investigate generic pipeline system behavior is demonstrated. The applicability of the three models is interpreted theoretically and their differences shown through application for (1) a one pipe-soil interaction element and along (2) a 100 m segment of pipeline. The latter shows the practical application of these models to offshore pipeline engineering examples, with the influence of a free span behavior investigated. The ability to model complex cyclic loading is also shown.