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Numerical study of steel pipelines kinematic distress due to secondary seismic fault rupture

Georgokitsos Nikolaos-Pelopidas

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Summary

Energy is undoubtedly one of the major issues for modern societies, as energy demands are constantly increasing, while the available resources are reduced and the adverse environmental impact on the planet is increased. The first pipeline networks that were used to transport hydrocarbons over large distances were constructed at the beginning of the 20th century. Nowdays, large-scale pipelines, mainly for the transportation of natural gas under high pressure, can be found worldwide, both onshre and ofsohore. Therefore, it is imperative to establish efficient design guidelines and functioning regulations to ensure their safe operation. In addition, optimal route selection of such large-scale networks requires extensive research of the wider region to collect geological, geotechnical, seismological, etc. data in order to ensure the safe operation of the pipeline and to minimize the risk to population and the environment.It is evident that potential damages can be particularly detrimental, both in environmental and financial terms. Although technology and construction practice are contantly upgraded, some of the existing pipelines do not fullfil contemporary design criteria, while construction defects and aging can deteriorate their safe operation. Accordingly, a pipeline must comply with existing regulations in order to minimize the propabilty of potential damges during its construction and operation within the whole life-cycle of the project. For this purpose, all necessary studies should be performed in order to identify and fully assess the impact of man-made and natural hazards, emphasizing on earthquake-related hazards and the consequent distress of the pipelines.Permanent ground displacements due to the rupture of seismotectonic faults have caused many pipeline failures. Hence, in areas with large seismic faults it is necessary to carry out a holistic aseismic design so that the pipeline can withstand substantial soil deformations due to its potential intersection with the main as well as secondary faults. Typically, after the necessary geological investigations, the main faults can be identified and, in some cases, avoided by selecting an alternative pipeline routing. However, several significant secondary faults can often occur in the proximity of the main fault. This hazard may not have been adequately assessed; thus, the pipeline may cross a secondary fault and can be exposed to a substantial risk, even analogous to the risk of crossing the main fault. In the relevant literature the studies on secondary ruptures are less compared to the ones for main ruptures, whille they are even more limited regarding the simultaneous rupture of main and secondary faults.The aim of the present diploma thesis is to investigate the response of a natural gas steel pipeline when crossing a secondary fault (aligned vertically to the main fault) in an attempt to avoid the main rupture. For this purpose, a detaild parametric investigation has been performed to assess the impact of the main parameters of the problem on the soil deformations and consequently on compressive and tensile strains of the pipeline. The obtained results are compared with those referring to the pipeline route crossing through the main rupture for the cases of normal and reverse main faults, as well as for the more complex case of oblique slip main fault rupture.

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