Best Practices for Developing Geotechnical Models and Seismic Hazard Procedures for Critical Infrastructure: The Viadotto Italia Case Study in Southern Italy

The performance of a large number of critical infrastructure systems needs to be periodically re-evaluated. This is especially so when such systems are located in seismic areas and are subjected to ageing effects. Seismic re-evaluations are typically performed using numerical response history analyses based on a geotechnical model of the infrastructure and using hazard-consistent ground motions. We depart from the Viadotto Italia (the tallest multi-span bridge in Italy, located in a highseismicity region) to draw best practices on how to construct a robust geotechnical model and derive appropriate target response spectra to be used in forward applications. Our proposed framework starts with the analysis of historical and new information and data. We then describe how to perform a multi-epoch consistency analysis that deals with the reliability and level of uncertainty of the data, culminating with the definition of a pragmatic geotechnical model that builds upon all available data, including investigation information produced at different spatial resolutions and quality levels. We also propose a consistent approach to perform site-specific probabilistic seismic hazard analysis to develop appropriate ground motions. This last step builds upon experiences with a data-rich high-seismicity zone in southern Italy, where both shallow crustal faults and deep subduction sources are present.