The interconnectedness of current urban life with infrastructures urges the decision-makers to consider the resilience of urban lifeline systems as a priority. This motivates the research presented here, where the performance of a complex urban gas distribution system in a city with more than 12 million resident population is evaluated under the effects of seismic-induced liquefaction. The paper reviews the liquefaction potential in the Greater Tehran Area, and identifies the inputs for the analysis of soil-pipe interactions. The performance assessment is carried out using both numerical (finite elements analysis) and small scaled experimental assessments, for validation of the numerical models. The experimental results indicate that the numerical models are adequate for the performance evaluation of buried pipelines. The assessment shows that the buried pipelines perform well in most areas of the city, however, structural damage is expected in areas with higher seismic demands. In such areas, hands-on countermeasures are proposed to mitigate the risk of liquefaction-induced damage on the buried pipelines system. The results, methodology and procedures can be used as a framework the similar urban infrastructure risk analysis and mitigation studies.

Introduction

Pipelines are among the most important lifelines in urban and metropolitan areas. Depending on their function, pipeline networks prevalently consist of reinforced concrete, steel, or polyethylene (PE) pipes. Pipeline systems are used for various purposes, including transmission, or distribution of gas, clean water, waste water, etc. Such distribution systems commonly consist of a network of buried pipelines, which are susceptible to structural damage during seismic events. In fact, in seismically active regions, earthquakes can be regarded as the most destructive natural hazard to buried pipelines. The dependence of the general public on continuous operation of buried pipelines makes structural damage to these lifelines following major earthquakes a public safety concern in large cities. Further, structural damage to buried pipelines used for the distribution of combustible, flammable, and/or toxic gases can lead to major secondary catastrophes. The severity of such risks and consequences are much greater in larger cities and would, therefore, require special consideration and risk mitigation by the stakeholders and the decisionmaking authorities. Given the vulnerability of gas distribution pipelines to seismic events, the socioeconomic importance of their operation, and the posthazard risks associated with structural damage to these networks, it is of great importance to identify the critical seismic mechanisms that can cause structural damage to the pipeline networks, assess their seismic performance in large cities, and mitigate their potential risk and damage. Previous studies on the performance of pipeline networks in large metropolitan areas include [1–۱۰].