This study aims to numerically analyze the axial force, shear force, and horizontal displacement in Tunnel B on the Pataveh-Dehdasht axis. The tunnel is part of a national project that was inaugurated in the summer of 2023. The project's technical specifications include 2.2 million cubic meters of earthwork, 2,100 meters of retaining walls, 110,000 tons of subbase and base layers, and 95,000 tons of asphalt. This study investigated the effect of tunnel lining thickness on shear force, axial force, and horizontal and vertical displacement using PLAXIS finite element software in a two-dimensional framework. Plane strain theory was employed with 15-node elements for modeling. The Mohr-Coulomb constitutive model, one of the fundamental stages in numerical analysis and a common model for tunnel excavation simulations, was applied to model the soil behavior of the study site. The results indicate that increasing the lining thickness reduces vertical and horizontal displacement at all points while increasing axial and shear forces. Maximum deformation occurs at the tunnel invert and minimum deformation occurs at the right sidewall of the tunnel. Increasing the lining thickness from 20 cm to 35 cm leads to a reduction of approximately 100% in tunnel floor settlement and a significant decrease in horizontal displacement exceeding 90% at certain points. These results demonstrate the importance of selecting an appropriate lining thickness for controlling deformations, enhancing load-bearing capacity, and improving the tunnel's seismic safety.
