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The convergence-confinement method (CCM) is a method that has been introduced in tunnel construction that considers the ground response to the advancing tunnel face and the interaction with installed support. One limitation of the CCM is due to the numerically or empirically driven nature of the longitudinal displacement profile and the incomplete consideration of the longitudinal arching effect that occurs during tunnelling operations as part of the face effect. In this paper, the authors address the issue associated with when the CCM is used within squeezing ground conditions at depth. Based on numerical analysis, the authors have proposed a methodology and solution to improving the CCM in order to allow for more accurate results for squeezing ground conditions for three different excavation cases involving various excavation-support increments and distances from the face to the supported front. The tunnelling methods of consideration include: tunnel boring machine, mechanical (conventional), and drill and blast. [ABSTRACT FROM AUTHOR]

A support system of weak rock tunnels typically consists of two components, namely an artificial support structure of combined categories and a rock mass surrounding the tunnel. Stability analysis and design methods of the artificial support structure have reached a mature developmental stage, whereas that of the surrounding rock has few progresses, especially when considering the surrounding rock as one of the support components. For this, from the perspective of considering the surrounding rock as one of the support components, an analytical method is proposed to calculate the factor of safety of the surrounding rock component, along with a stability analysis method for the complete tunnel support system (i.e. surrounding rock combined with artificial supports). This analytical method is based on an evaluation approach developed to obtain the stable ultimate deformation of the tunnel's surrounding rock, along with the minimum internal pressure to stabilize the tunnel. The evaluation approach is on the basis of the generalized Hoek–Brown yield criterion that is considered as the non-linear behaviour of the rock mass, combined with Rabcewicz's mode of initial instability as well as Carranza–Torres's solution to tunnel deformation. The validity of the developed evaluation approach is verified by comparing the results to numerical simulation outputs and field data. A comprehensive parametric analysis is also conducted to investigate the effects of parameters involved in the evaluation approach on the stable ultimate deformation and minimum internal pressure. Subsequently, a suggestion is made aiming to revise the notion of 'optimal installation timing' of artificial supports for classical support design methods. This research forms a complete set of quantitative analysis tools for the stability and design of the support system of underground tunnels excavated in weak rocks. [ABSTRACT FROM AUTHOR]