The Seismic Behavior of Urban Tunnels in Soft Saturated Soils

Abstract

Damages of the life lines were observed first in Nigata earthquake (1964) and then in the Alaska earthquake. After that, discussion about the earthquake effects on the underground structures became an important issue. Therefore, several studies were carried out about dynamic analyses of the underground structures. In Kobe earthquake (1995), most of the devastations happened in several urban subway. Taiwan earthquake (1999) is one of the examples of damages of underground structures in which many tunnels in the city center were highly damaged. 1999 Earthquake in Turkey is another example of subway structure damage in which highway tunnels were damaged severely. Also, several reports exist about the damages of large underground structures. Tangshan earthquake in china (1976) and Loma prieta earthquake in America (1989) are some examples of these kinds. Thus, many studies have been designed to focus on the effects of earthquake loading on the forces and displacements of underground structure. Gradual increments of excess pore pressure in soft saturated soil layers during earthquakes led to a decrease in the effective stress and this mechanism of underground structure seismic behavior has not been fully recognized; and despite the presence of several studies that have been conducted already, many others are still needed. So the present study strives to assess the effect of seismic behavior of urban tunnels as a life line in soft soils. In this paper the FLAC software has been used to model the pore pressure changes during earthquakes. The studies thus far have been focused on the impact of increasing the pore pressure and decreasing the effective stress in soft saturated soil on the tunnels constructed in this area.