Optimal Route Selection of Offshore Pipelines Subjected to Submarine Landslides

Abstract

Offshore lifelines (i.e., pipelines and cables) are usually vulnerable to seabed deformations induced by earthquake-triggered geohazards, such as submarine landslides, soil liquefaction, and tectonic faulting. Since the complete avoidance of all areas characterized by offshore geohazards is not always techno-economically feasible, optimal lifeline route selection is deemed necessary for the safety and serviceability of every such infrastructure, in order to minimize the risk of severe environmental and economic consequences. The current study presents a decision-support tool for the design of offshore high-pressure gas pipelines, capable of performing: (a) the assessment of submarine landslides along a possible pipeline route (i.e., impact force and landslide width), (b) the assessment of their potential impact on the pipeline (i.e., pipeline strains), and (c) the optimal pipeline route selection. The advanced capabilities of GIS in lifeline optimal route selection are successfully combined with efficient (semi-)analytical models that realistically assess the response of offshore pipelines when subjected to axial or oblique loading conditions due to a submarine landslide. The efficiency of the smart tool is presented through a case study of an offshore pipeline that is crossing potentially unstable slopes -under static and seismic conditions- in Adriatic Sea. Five alternative routings are proposed based on the adopted design criteria when crossing the seismically unstable slopes and zones characterized by steep inclination. Provided that sufficient and reliable data are available, the developed decision-support tool can be efficiently used for deriving the potentially optimal route of an offshore pipeline.