The purpose of this research is to study the earthquake's effect on segmental lining and to analyze stresses and displacements formed in contact surfaces (joints) between segments as a result of dynamic loading. The case study for this research is Alborz twin tunnels in the TEHRAN-SHOMAL FREEWAY. After excavating a pilot tunnel, 5.2m diameter, by use of TBM, enlargement of the pilot tunnel will be performed to reach 12m diameter. In this research UDEC (Universal Distinct Element Code) is used for numerical modeling. First, static conditions are analyzed, in which stages of excavation are considered. After applying the primary and permanent support, various static loadings on segmental lining are taken into account. Then Seismic Hazard Analysis is performed and Peak Ground Acceleration (PGA) for Design Base Earthquake (DBE) and Maximum Credible Earthquake (MCE) in tunnel site is determined. Afterwards, earthquake loading is applied. For this purpose the selected accelerogram is modified for the two levels of dynamic loading. Then two properties (real and fictive) are considered for the joints. Finally the amounts of stress and displacement of joints are investigated as a result of dynamic loadings and for each case the factor of safety is calculated. The worst factor of safety is determined about 2.
Underground facilities built in areas subject to earthquake activity must withstand both seismic and static loading. Historically, underground facilities have experienced a lower rate of damage than surface structures. Nonetheless, some underground structures have experienced significant damage in recent large earthquakes, including the 1995 Kobe, Japan earthquake, the 1999 chi-chi Taiwan earthquake and the 1999 Kocaeli, Turkey earth quake [1]. Sharma and Judd (1991) generated an extensive database of seismic damage to underground structures using 192 reports of underground behavior from 85 earthquakes throughout the world. Among them 94 cases of underground damage were identified while in the other 98 cases no damage was reported. They developed a correlation between peak ground acceleration (PGA) of the surface, overburden depth and damage [2]. Earthquake effects on underground structures can be grouped into two categories:
ground shaking; and
ground failure such as liquefaction, fault displacement, and slope instability. Ground shaking (which is considered in this paper) refers to the deformation of the ground produced by seismic waves propagating through the earth's crust. The major factors influencing shaking damage are:
The shape, dimensions and depth of the structure
The properties of the surrounding soil or rock
The properties of the structure; and
The severity of the ground shaking (PGA). Determining the deformations resulted from ground shaking can become complex; therefore the behavior of a tunnel is sometimes approximated to that of an elastic beam subject to deformations imposed by the surrounding ground. Three types of deformations express the response of underground structures to seismic motions:
Axial compression and extension
Longitudinal bending
Ovaling/racking [1].
