Buried steel pipelines for water and hydrocarbon transmission in seismic regions may be subjected to large imposed deformations. When a buried pipeline crosses an active strike-slip fault, the relative motion of the two soil bodies in which is it embedded can lead to significant deformation of the pipeline and possibly to loss of containment.
To be able to fully understand the effects of this movement and the interaction between pipe and soil on the strain demands in the pipeline, a novel full scale experimental setup has been developed. To allow accurate monitoring of the pipeline deformation, the pipe-surrounding soil has been replaced with appropriate nonlinear springs, leaving the pipe bare during the experiment.
In a total of ten tests, the strain demand in a pipeline as a result of these ground-induced deformations has been investigated. The testing program includes variations of pipeline geometry, steel grade and internal pressure. Furthermore, cohesive and non-cohesive soils have been simulated in the tests. Observed responses of the pipeline include local buckling, high tensile strains (up to 5%) and, in one case, cracking of the pipeline.
Based on experiences with these experiments, a numerical model has been developed that uses non-linear springs to model the pipe-soil interaction. By modelling the pipe and soil conditions that were simulated in the ten experiments, this model has been calibrated and validated. Comparisons between the model predictions and test results show that the numerical model is able to predict the deformational behavior of the pipeline accurately. Moreover, also the formation of local buckles is predicted with satisfying results. The results of the validation operation lead to the conclusion that the new model is performing well. By omitting the modelling of the full soil body, computation time is reduced, increasing practical use of the developed model.
Numerical model of formation of a 3-D strike-slip fault system
