The convergence-confinement method is a tool that enables us to give an appreciation of the nature of the interplay between the rock-mass and the support, and the effect of the variation in the properties of the rock on the support load. From a theoretical scope, the approach to the tunnel behaviour is rigorous. However, this technique is not much used in practice. We think this is due to some reasons, which are briefly reviewed in this article. A significant issue for a reliable application of the approach is which behavior model is selected, together with the inaccuracy of the longitudinal deformation profiles. This work intends to discuss some of these topics.
The convergence-confinement method (CCM) consists of three basic components in the form of three graphs: the longitudinal deformation profile (LDP), which relates tunnel deformation to distance to the tunnel face; the support characteristic curve (SCC), which represents the stress–strain relationship in the support system; and the ground reaction or response curve (GRC). From a physical-mathematical scope, the general approach and solution of the tunnel behaviour and ground reaction curve seems to be smart. However, this approach has not been and is not widely used in engineering practice. This is due to several reasons, among which the following can be highlighted:
The stringent initial assumptions needed to obtain analytically the GRC,
The difficulties to adequately define the behaviour and characterize the rock mass,
The rigorousness of the calculation procedure,
The lack of clear indications on when and how to use it. There are apparently different proposed criteria for its field application,
The difficulties associated to the correct construction of the support and reinforcement characteristic curve SCC and the LDP