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Seismic vulnerability assessment and minimization of seismic risk of offshore and coastal energy lifelines

Chatzidakis Dionysios

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Summary

Hydrocarbons, such as natural gas and oil, are very important energy sources of modern era. The increasing energy demands of the modern civilization has led to the continuous exploitation of new onshore and offshore deposits. Large-scale pipeline networks are often used to transfer hydrocarbons to the industrial and urban centers. Such pipelines are strategically important infrastructure and they are often the subject of intense controversy between companies and countries. Moreover, a pipeline failure can cause incalculable damage and devastating consequences to the society, the economy and the environment. Pipelines may extend for hundreds of kilometers, both onshore and offshore, laying on the seabed at depths of hundreds of meters, under highly adverse and uncertain conditions. As a result, they are exposed to a wide range of both natural and man-made hazards. Seismic geohazards, such as strong ground motion, fault ruptures, landslides and soil liquefaction, are among the most important hazards that pipelines have to overcome. The transient and permanent ground displacements from the above phenomena can cause major damage to pipelines. During the last decades, many analytical, computational and experimental studies have been conducted to investigate these topics. These studies have led to the development of international and national standards and regulations for the seismic design of pipelines. Moreover, several methodologies have been developed for the simulation of pipe response, as well as for mitigation measures that can be used to protect the pipelines. However, all the above are focused mainly on onshore pipelines, and there is lack for analogous studies regarding offshore and coastal pipelines. The present Doctoral Dissertation focuses on the investigation of offshore and coastal pipelines by thoroughly investigating their response under seismic kinematic distress and the development of methodologies for their optimal seismic design. These goals are achieved through the development of advanced analytical and numerical methodologies, utilizing classic theory of mechanics, analytical solutions, finite element and difference methods, etc. The simulations are conducted utilizing realistic data and assumptions which are derived from experimental studies, field investigations and analytical methodologies. The results of this research are compared with the corresponding ones from experimental and numerical studies to ensure that they are realistic and reliable. For the practical applicability of the proposed methodologies, realistic topographical, geological and geotechnical data are used from the east Mediterranean Sea and the Trans Adriatic Pipeline (TAP). Pipe-soil interaction is simulated according to the proposed methodologies from contemporary international guidelines. Conclusively, the first goal of the Ph.D. Thesis is the investigation of offshore pipelines under kinematic distress due to landslides for different intersection angles of the sliding mass with the pipeline. In the sequence, the propagation of secondary faults through soil deposits is investigated. The kinematic distress of pipelines due to the intersection with secondary faults is also investigated. The presence of secondary faults is a frequently occurring phenomenon, which has not been addressed yet regarding its impact on pipeline distress. The third goal of the Doctoral Dissertation is to compare the effectiveness of different mitigation techniques when applied to deep-sea pipelines, which are usually led directly on the seabed. The range of the applicable mitigation techniques on such pipelines is limited due to the high costs and the technical difficulties involved. Finally, the developed methodologies are implemented in a suitable computational tool to achieve route optimization of offshore pipelines.

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