The seismic stability of underground structures is one of the most complex aspects of geotechnical earthquake engineering. Among various factors influencing tunnel behavior, groundwater plays a crucial role in altering stress distribution, displacement, and internal forces. In this study, the influence of groundwater level on the seismic behavior of circular tunnels located in seismic regions is analyzed using the finite element method through PLAXIS 2D software.

The interaction between soil, structure, and pore pressure under dynamic conditions is modeled for three groundwater levels: below the invert, along the tunnel axis, and above the crown. The results indicate that increasing groundwater level reduces axial force and bending moment within the tunnel lining, with up to 55% and 40% reductions at the crown under dynamic loading, respectively. Pore pressure variations were found to significantly affect effective stress distribution, and uncontrolled groundwater levels could lead to instability under seismic excitation. The outcomes of this research provide practical guidance for seismic design of tunnels in saturated and high-water-table regions.

Keywords: Tunnel, Groundwater, Seismic Analysis, Finite Element Method, Geotechnical Stability