The diagnosis phase

Abstract

The diagnosis phase is that in which the design engineer uses the information collected during the survey phase to formulate predictions of the deformation behaviour of the tunnel (extrusion, preconvergence and convergence) in the absence of stabilisation intervention. The result is the division of the underground alignment into sections with uniform deformation behaviour, identified in terms of three basic behaviour categories:

• category A: stable core-face or rock type behaviour;

• category B: stable core-face in the short term or cohesive type behaviour;

• category C: unstable core-face or loose type behaviour