Nader Hatef - Professor, Department of Civil Engineering, School of Engineering, Shiraz University, Iran.
Ali Roozitalab - Department of Civil Engineering, School of Engineering, Shiraz University, Iran.

The tunnels play an important role in developing countries and in communities are vital arteries. So, safety and stability of such structures is important in engineering is important because it predicts and analyzes the behavior of the structures surrounding them, it is very complicated and difficult. The forces involved in the design of structures that are not well known, are the earthquake forces. Has long been believed to be due to exposure to the soil environment, the earthquake has no significant effect onthe tunnel. But it is now clear that these structures are due to be buried and length, have somecharacteristics that made their seismic behavior distinct from the majority of the surface structures. Buried structures, particularly tunnels depending on the geometry, the depth of the surface of variousfactors geotechnical, structural and seismic earthquake show different behaviors of themselves. Themost important points in the design of tunnels should be considered is the uncertainty about the parameters of the soil and seismic parameters. Although losses incurred in these structures during an earthquake are less than the superficial structures, but studies suggest that can be severe at times the force-bearing structures as a result of earthquake damage. In Iran, too, according to the country seismicity and increasing construction of tunnels and underground structures in different regions of the country, it is necessary to have a comprehensivestudy done in the field of seismic design of tunnels. An important issue in the design and analysis of the seismic performance of the tunnel and in fact, acareful study of seismic stability of road and rail tunnels can be considered as the main topic in tunnel engineering. Many tunnels are constructed in areas with high seismic potential. Given that these tunnels are often forced transition location and the route so it cannot be changed, and, on the possibility of earthquakes with high damage on them, so a plan to construct a safe and efficient tunnel is required.