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Geomechanical Tunnel Design by Convergence-Confinement Method

3D Nonlinear Simulation of Escavation and Lining Installation

This simulation shows a tridimensional application of the Convergence-Confinement Method for geomechanical tunnel design. In this study, the in-situ stresses are calculated first, by modelling the nonlinear geomechanical properties of soil with the well-known Mohr-Coulomb criterion.
Taking into account this initial stress distribution, the tunnel excavation is simulated. Before the installation of the tunnel lining, a so-called relaxation coefficient equal to 30% is considered. After the installation of the tunnel structure, the soil confinement is completely removed and additional loads such as water pressure are applied. With this procedure, the observed soil relaxation in the period of time between the tunnel excavation and the lining installation can take place.
The computed internal forces in the tunnel structure, which is modelled with shell elements, allow the calculation of the necessary steel reinforcement according to the main civil engineering standards such as Eurocode. The particular geometrical shape of the considered tunnel section, where an emergency exit is present, yields asymmetrical results.
This study focuses only on the steel reinforcement resulting from the Ultimate Limit States calculation, while the required reinforcement for limitation of concrete cracks width and minimum amount of bonded reinforcement are not shown.

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