An investigation on the applicability of the convergence confinement method to a deep rock tunnel for different conditions

Numerical modelling with finite element programs, allows users to model an underground opening almost exactly in relation to its actual situation in reality. However, the engineering analyses that are performed using analytical methods may be more economic and less time consuming. The overall objective of this research was to investigate application of the convergence confinement method for the design of a deep tunnel, with the ultimate goal of providing a better understanding of the method. First, a case study of Chamoise Tunnel (France) which is reported in the literature, is regarded as case study to create synthetic data sets for this research. Different analyses are conducted by using the finite element approach and analytical approach to establish a comparative study between the obtained results. The numerical models that are created to simulate uniform loading (K0=1.0) conditions for a deep circular tunnel were altered to study different geometry, non-uniform loading conditions (K0=0.6 and K0=1.2) and a different number of excavation stages. As a result of investigating the above mentioned variables; occurring convergences around the tunnel contour were found to be increased as the tunnel shape changes from a fully circular tunnel to a circular-arc shaped tunnel and as the initial ratio of the horizontal stresses to the vertical stresses (K0) increases in [0.6, 1.2]. A good match has been detected between the numerical and analytical approaches for the excavation induced radial displacements for the case where tunnel is unsupported. However, it is not possible to conclude the same for the radial displacements developed in the case where the tunnel is supported. A further research may be appreciated to comprehend the behaviour of the supported rock-mass.