Performance of a buried pipeline along the dip of a slope experiencing accidental sliding

Abstract

Contrary to highways, major pipelines often have to be installed crossing hills or mountain ridges, following the dip of the slope. Slope movements that may be triggered by an earthquake, heavy rainfall, an excavation at its toe, or long-term creep, constitute major hazards that must be considered in design. This paper studies numerically the interaction of a steel pipeline with a rotational slide originating at the crest of a slope and evolving in the direction of the pipeline axis. Different pipeline-slide mechanisms are examined: a reference slide taking place in a rather shallow slope in which the sliding surface crosses the pipe over its straight portion, a deeper scenario where the toe of the slide interacts with the bottom elbow element of the pipeline, and two much steeper scenarios. A two-step finite-element methodology is developed and validated against several published experiments. The analysis simulates realistically the soil sliding process and all possible modes of pipeline failure. The pipeline performance is discussed for a range of internal pressure scenarios: from empty to full operating at maximum allowable pressure (pmax). It is found that the relative position of the slip-line to the pipeline axis (at their intersection) determines the amount of bending induced in the pipeline and eventually the vulnerability of the installation. For empty pipes the prevailing failure mode is inward buckling, whereas pressurised pipelines rupture at larger displacements due to excessive accumulation of tensile strains. When the slip-line of the sliding mass crosses the toe of the slope, excessive bending is experienced at the lower bend of the installation, which is translated into a compressive force, invariably speeding up pipeline failure. Here the failure mode is always buckling: inward for non-pressurised pipes and outward for non-zero internal pressures.