Ilam tunnels inspection, maintenance, and rehabilitation: A case study

•Fully coupled 3D finite element analysis of tunnels.•High failure potential, especially in cases of an earthquake event.•A new precast segmental system has been developed and introduced.•Filling the available cavity behind the linings can lead to better stability. Due to the complexities of design and technical issues of construction, tunnels are considered to be enormous financial investments. Therefore, rehabilitation with the purpose of providing a higher life span is essential. Underground facilities usually have a higher service period than expected when designed, which often requires regular inspection. This study aims at providing a guideline for future tunnel investigations and maintenance. Offered solutions with regard to different cases of an anomaly for three available tunnels in the Ilam province have been introduced. These currently servicing tunnels are usually constructed as unlined rock tunnels excavated, using controlled blasting. Masonry, reinforced concrete, and shotcrete lining systems have been used in the collapsible zones. These infrastructures as part of the transportation network of the Ilam province in Iran are located in one of the most active seismic, as well as high rainfall zones in the Middle East. Aging and degradation of material alongside recent earthquake activities can lead to massive destruction of the tunnels if regular maintenance work doesn't take place. All tunnels were evaluated using advanced numerical analysis methods. Stress and displacement values ​​in the rock mass and different lining systems have been investigated using various analytic methods and the rehabilitation programs for tunnels were developed and introduced. The high risk of failure in the tunnel in the Payambar tunnel is predicted in cases of a seismic event affected by the inclination of rock layers. Methods of rehabilitation have been proposed to improve stability and decrease deformations. The formation of icicles in the Azadi tunnel during the cold seasons have been solved through employing a temporary water drainage system. Unlined tunnel sections were planned to be covered with reinforced concrete lining and both cast-in-place and precast segmental lining systems have been proposed. In the Shabab tunnels an extremely disturbed, 2–3 m deep rock layer was found between the masonry lining and the top of the tunnels, due to its controlled blasting excavation technique. Filling the voids using a pressure grouting technique was discovered in orde