Inclined and Uplift Resistance of Pipelines Buried in Rock-Paper

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The study investigates how rock berm geometry and pullout direction affect the resistance of buried offshore pipelines to buckling-related movement. Researchers tested pipes embedded in trapezoidal rock berms using 1:15-scale centrifuge experiments and 1:2-scale, single-gravity tests. The tests varied berm height and width and applied loads at inclinations from 10° (mostly horizontal) to 90° (vertical).<br /><br />Resistance increased as loading became more horizontal: at low inclinations, peak resistance was typically about five times that under vertical pullout. More horizontal loading also required greater pipe displacement to mobilise peak resistance. Higher and wider rock cover further increased resistance.<br /><br />Measurements of horizontal and vertical force components were used to establish part of a failure envelope. When forces were normalised by pipe diameter, embedment and effective unit weight, the results indicated that a common envelope could describe different berm heights.<br /><br />Results from the two testing scales generally agreed, supporting the use of the adopted dimensionless groups for rock berms. Most corresponding peak resistances were within about 10%; larger differences in some low-inclination tests were attributed to the centrifuge loading frame becoming buried and mobilising additional rock.<br /><br />The findings show that pipeline resistance cannot be assessed from vertical uplift tests alone: load direction and berm geometry have a substantial influence on both the resistance and the displacement needed to mobilise it.

Keywords

offshore pipelines

rock berm geometry

pullout direction

buckling resistance

centrifuge tests

single-gravity tests

trapezoidal berms

failure envelope

dimensionless normalization

pipeline uplift