The aim of this study is to numerically analyze the axial force, shear force, and horizontal displacement in the tunnel (Tunnel B on the Pataveh-Dehdasht axis). This tunnel is part of a national project, which was inaugurated and put into operation in the summer of 2023, with technical specifications including 2.2 million cubic meters of earthwork, construction of retaining walls with a total length of 2,100 meters, 110,000 tons of subbase and base layers, and 95,000 tons of asphalt.
In the present study, the effect of tunnel lining thickness on shear force, axial force, and both horizontal and vertical displacements was numerically investigated using the PLAXIS finite element software in a two-dimensional framework. Plane strain theory was employed with 15-node elements for modeling. For the surrounding soil, the Mohr-Coulomb constitutive model, which is one of the fundamental stages in numerical analysis and commonly used in most tunnel excavation simulations, was applied to model the soil behavior of the study site.
The results indicate that increasing the lining thickness reduces both vertical and horizontal displacements at all points, while axial and shear forces increase. The maximum deformation occurs at the tunnel invert, and the minimum occurs at the right-side wall of the tunnel. Increasing the lining thickness from 20 cm to 35 cm leads to an approximately 100% reduction in tunnel floor settlement and a significant decrease in horizontal displacement, exceeding 90% at certain points. The findings highlight that selecting an appropriate lining thickness plays a key role in controlling deformations, enhancing load-bearing capacity, and improving the seismic safety of the tunnel.
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