The Convergence-Confinement Method: Roles and Limits in Modern Geomechanical Tunnel Design

The convergence-confinement method, based on the analysis of the stress and strain state that develops in the rock around a circular tunnel, has been presented in this study with the two analytical solutions that have been most frequently used in recent years. Problem statement: Thanks to the increased power of electronic processors and the spread of numerical methods, the role of the convergence-confinement method had changed but nevertheless remains important in the geo mechanical design of tunnels. Approach: Apart from being a basic instrument for the preliminary design of support and reinforcement structures, it can be profitably used for the estimation of the loads that act on the support structures, of the thickness of the plastic zone at the tunnel boundary, of the expected convergences and it can also be used to obtain an estimation of the geo mechanical parameters of the rock mass, through back-analysis staring from the in situ measurements. Conclusion: This study illustrated the fields in which the method still presents important practical applications and also its greatest limits, in more detail.