Finite Element Modeling of Buried Pipelines Subjected to Seismic Loads: Soil Structure Interaction Using Contact Elements

Buried pipelines pass under lands exposed to traffic, railroads and highways, and cross through seismically active lands. The pipelines are exposed to the combined loads of soil weight, traffic load and seismic loads, and internal pressure. Several design practices exist for the combination of stresses due to soil, seismic and traffic loads, such as ASME design guide, VDTUV 1063, and DIN 2413. However, the soil structure interaction is not considered especially in the case of seismic loads. When the pipeline loses its support due to soil liquefaction then the problem can only be solved using the finite element method. Customarily, spring elements have been used to model the pipeline-soil interaction under the combined action of action of seismic, soil and pressure loads. This meshing technique, however, is tedious and time consuming. Furthermore it requires the analyst to kill spring elements that are not active. Verification of the model is thus difficult and prone to errors. In this work frictional elements are used to model the pipeline-soil interaction. This meshing technique is automatic and it does not require keeping track of the contact surfaces. The soil surface is the contact surface and the pipeline outside diameter is the target. The pipeline can be modelled as either a contact surface or a contact line depending on the dimensionality of the model.