Recent Advances in Seismic Vulnerability Assessment of Tunnels and Underground Structures

Abstract

Tunnels and underground structures are constructed at an increasing rate in seismic prone areas to facilitate expanding transportation needs. The importance of these types of structures in modern societies, as well as the significant downtimes associated with seismically induced damage on them, led to an increasing interest of the scientific community and practitioners on the vulnerability assessment of this infrastructure against seismic hazard. Various methodologies have been recently proposed to estimate the vulnerability of bored tunnels in rock or alluvial and cut and cover or underground structures, e.g., subways, in alluvial, against ground seismic shaking and earthquake induced ground failures. This paper discusses critical aspects of these methodologies, based on a thorough review of relevant state-of-the art, carried out in the frame of research project INFRARES (www.infrares.gr). Emphasis is placed on the numerical tools employed to estimate analytically the fragility of examined structures in relevant studies, the constitutive models used to simulate the seismic response of ground and structures, the determination of the capacity of examined structures, the selection of appropriate seismic intensity measures, methods used to develop rational probabilistic seismic demand models, the estimation of uncertainties related to seismic vulnerability of underground structures, as well as the methods for selecting fragility functions from existing ones in assessment studies of actual case studies. Through the discussion, acknowledged gaps in the literature are highlighted and topics calling for further investigation are presented. In addition, an up-to-date database of available fragility functions for tunnels and underground structures developed within INFRARES is presented.