Underground structures are generally considered less vulnerable to earthquake activity than surface structures. However, there are practical cases in which this assertion needs to be verified. Even if dynamic effects are small, response of underground structures may impose significant loads on the support system, which have to be included. This paper discusses the modeling of Esfahan subway twin tunnels subjected to earthquake and interaction of tunnels. In critical structures like subway tunnels, performing a time history dynamic analysis is the only acceptable method for determining the seismic-induced forces. For sites with no recorded earthquake ground motion, artificially generated accelerograms to represent the real earthquake records has been suggested by many experts. This paper addressed the modeling of subway twin tunnels subjected to earthquake with FLAC. Finite difference model is developed to estimate the long-term support system.
In modern urban areas, underground facilities, including subways, underground roads, underground storage tanks and common utility ducts, are essential to human life. Hence, in critical structures like subway tunnels, performing a time history dynamic analysis is the only acceptable method for determining the seismic-induced forces. Underground structures are generally considered less vulnerable to seismic action than above ground structures. However, even if dynamic effects are small, response of underground structures may impose significant loads on the support system, which have to be included. The intention of this paper is to introduce one of these lifeline facilities, namely the seismic design of Esfahan Metro tunnel. Esfahan is one of the largest and most well known cities in Iran. With the rapid economic development and reform of the last two decades, construction activities of civil infrastructures and buildings in the Municipality of Esfahan have been increasing significantly. Underground structures do not fall in resonance with the ground but respond in accordance with the response of the surrounding ground. Although, generally, underground structures exhibit a better performance than surface structures, in some situations they may be particularly vulnerable to seismic loading depending on:
the size, shape and depth of underground structure;
the geotechnical ground conditions; and
the severity of ground shaking.
Regardless of the qualitative definitions of earthquake, an engineer concerned with design of underground structures requires that the seismic environment be defined in a quantitative manner. Specifically, the characteristics of earthquakes and ground motion pertinent to the development of seismic input criteria are the size of the earthquake, the intensity and the frequency content of the ground motion, and the duration of strong shaking . The assessment of underground structure seismic response, 1000 therefore, requires an understanding of the anticipated ground shaking as well as an evaluation of the response of the ground and the structure to such shaking. Iran is one of the most seismic countries of the world. It is situated over the Himalayan- Alpied seismic belt and is one of those countries which have lost many human lives and a lot of money due to the occurrence of earthquakes.