In this paper, the forces acting on tunnel lining due to dry condition and groundwater pressures were studied. Firstly, the effect of the forces acting on tunnel lining under dry condition was studied numerically for the Sabzkouh tunnel as an actual case study. This tunnel is a deep tunnel that is bored through Zagros Mountains in Iran by a hard rock Tunnel Boring Machine (TBM). Secondly, the effect of hydrostatic pressures on tunnel lining was evaluated. The lining of a bored tunnel usually consists of precast concrete segments that are reinforced by steel bars. These segments must be capable to withstand all loads caused by earth (e.g. rock and water pressures), construction conditions (e.g. thrust forces) and utilization (e.g. traffic loads) without unallowable deformations. A Finite difference code was used to analyze Sabzkouh tunnel lining. The final results show that the values of bending moments, axial forces and shear forces in the precast concrete lining can be reduced under fully-drained conditions, although, the drainage is more effective in weak rocks rather than strong rocks.
In recent years, mechanized tunneling has developed increasingly, and the benefits of full-face tunnel boring machines have been recognized. Design methods for segmental tunnel linings used in mechanized tunnel constructions typically employ numerical bedded beam models and/or classical analytical solutions for the determination of structural forces (i.e. moments and shear and axial forces) and simple load spreading assumptions for the design of the reinforcement in joint areas (Gall et al., 2018). Basically, the forces acting on the tunnel lining depend on construction procedures and in many cases, these forces enhances during construction rather than after construction. The measurement of the induced bending moments and normal forces are difficult, but the numerical analyses give more reliable results than analytical and closed form solutions. The behavior of lining segments is affected by the complex construction features, for example the sequential excavation process and backfill grouting. Therefore, developing a framework to accurately predict the lining forces and deformations is essential for the purpose of structural safety and optimum design (Zhao et al., 2017).
