Thesis title: Risk Assessment from Multiple Hazards in Underground System
This dissertation presents a comprehensive framework for multi-hazard risk assessment in underground infrastructures, focusing on the interplay between earthquakes, structural collapse, fire, and evacuation dynamics. A detailed investigation into seismic geostatistics-4D, Incremental Dynamic Analysis (IDA) and structural fragility, fire in confined environment, and the analysis of evacuation conditions is conducted. The analyses consider the probabilities of events that single (earthquake/structural collapse/fire happening on its own) or not mutually exclusive (such as seismic-induced structural collapse, which may or may not lead to a fire), independent (which occur without affecting probabilities of occurrence of others) and non-independent (where one event increases/decrease the probability others). Through the Gu@larp mathematical model, the study offers a refined approach to multi-hazard risk-based design for underground infrastructure. The dissertation is organized into five macro-chapters.
Chapter 1 introduces the need for a comprehensive framework to assess multi-hazard risks in underground infrastructures. These systems, which play an essential role in urban environments, face increased risks from both natural and human-made hazards, including seismic events, structural collapse, and fires. The study aims to address these vulnerabilities by developing an integrated quantitative risk assessment framework that combines these hazards into a unified approach. The chapter outlines the specific challenges currently faced in multi-hazard risk assessment, such as the absence of methodologies that consider the interactions between multiple hazards and the importance of accurate scenario identification. Through clearly defined objectives, such as advancing risk modelling techniques and understanding in depth human behaviours and transfer it to evacuation analysis, Chapter 1 sets the stage for the technical analysis and methodologies that will follow.
Chapter 2 provides an in-depth analysis of the hazards affecting underground infrastructures, focusing on the integration of seismic, structural, fire, and evacuation risks. It begins with an in-depth review of the current state of knowledge with a discussion on seismicity and hazard estimation methods tailored to underground environments, introducing seismic geostatistics-4D analysis as a novel tool for capturing the spatial and temporal complexity of seismic data. The chapter also explores seismic-induced structural collapses. And fire dynamic is examined through the lens of tenability limits in confined spaces. Evacuation challenges are addressed, focusing on the dynamics of underground environments during fires and earthquakes
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while dispelling misconceptions about human behaviour in emergencies. The comprehensive risk analysis framework integrates these hazards, providing insights into societal influences on risk perception and advancing methodologies for a multi- hazard risk assessment model that considers both individual risks and their interdependencies to ensure the safety of underground infrastructures.
Chapter 3 focusing on developing a comprehensive multi-hazard risk assessment framework, analysing joint occurrences of different hazards. Theoretical foundations, including the integration of Aristotelian logic and complex systems theory, support scenario identification and modelling for multi-hazard modelling. The ALARP principle is discussed through legal and philosophical perspectives. The ALARP principle and the consideration of Black Swan events in a multi-hazard framework necessitate an expanded range of probabilistic concepts, encompassing basic unconditional probabilities and extending to complex multi-conditional probabilities. This broader spectrum provides a foundational basis for probabilistic approaches in analysing hazards within multi-hazard risk assessment. Key four risk indicators are used to evaluate risk exposure, aligning with ethical principles for Gu@larp method, combining scenario quantic-modelling with ALARP, providing a comprehensive framework for multi-hazard risk assessment.
The interest of the dissertation proposed here concerns the improvement of modelling support for the design and assessment of seismic and fire risks for the structural components of underground environments: An example developed and presented in this dissertation is the analysis of the specific seismic actions related to the damage simulated on the blocks in the CERN underground environment, where fires developed either independently or due to falling blocks, with evacuation scenarios based on human behaviour considered during these events. This dissertation in Chapter 4 applies advanced modelling techniques to characterize these scenarios, integrating seismic geostatistical-4D analysis (CoKriging), structural analysis (IDA), fire modelling (FDS), evacuation modelling (PBD), all within a quantitative multi- hazard risk assessment framework (Gu@larp).
Key conclusions highlight the importance of understanding multi-hazard scenarios to enhance safety in underground environments in Chapter 5. And limitations of the study are acknowledged, along with recommendations for future research directions.