Seismic vulnerability of tunnels and underground structures revisited

The procedure for seismic design of underground structures is well established and involves a phased approach of increasing levels of analyses as required for a given project. For seismic shaking in soil and rock, an empirical approach is first taken by assessing the level of damage using damage criteria graphs. These damage criteria graphs were developed based on empirical evidence of numerous case histories and relate ground motion intensity (peak ground acceleration or velocity) to the damage level. Previous investigators presented damage criteria graphs which were developed using old and less well documented case histories and attenuation relationships now considered outdated. Recent seismic events such as the 1989 Loma Prieta, 1994 Northridge, and 1995 Kobe earthquakes have provided illuminating case histories, suggesting some revisions to the earlier studies. As a part of a study on the Seismic Vulnerability of Tunnels for the National Center for Earthquake Engineering Research and the Federal Highway Administration, the authors of this paper reevaluated the existing seismic damage criteria and added new case histories to the existing data base. Also, as a part of this study, the authors investigated aseismic aspects of tunnel design.