Soil-buried pipeline interaction for vertical downwards relative offset

A new perspective is presented on the interaction effects for the vertical downwards offset of a pipeline relative to its surrounding soil. Instead of estimating the interaction force via shallow footing bearing capacity theory, as per common pipeline design practice, we assume that the vertical movement of the pipeline in uniform soil is governed by mechanisms similar to the lateral loading of a circular pile up to its limit load. The validity of this assumption is investigated numerically with the finite element limit analysis method, and design expressions are derived for the maximum interaction force on pipelines embedded in cohesive and granular soils. For the common case of buried pipelines built in sand-backfilled trenches, the same numerical method is employed to determine the necessary trench dimensions so as to avoid interaction with the possibly much stiffer native soil that results in a significant increase in the force applied on the pipeline during ground movement. The described approach can be employed in project-specific analyses to optimize trench dimensions, and thus avoid unnecessary excavation costs or mitigation measures.