Applicability of the Convergence-Confinement Method to Full-Face Excavation of Circular Tunnels with Stiff Support System

Abstract : 22 23 The ConVergence-ConFinement (CV-CF) method is widely used in conventional tunneling at 24 a preliminary stage of the design. In this method, the rock-support interaction is simplified by 25 means of a two-dimensional plane-strain assumption. However, when the ground exhibits large 26 deformation and/or when the support is very stiff and installed close to the tunnel face, the 27 results obtained with the CV-CF method may significantly differ from those obtained using 3D 28 numerical computations. The strong interaction taking place between the rigid lining and the 29 rock mass is not considered in the most common use of the CV-CF method. Some 30 improvements of the CV-CF method as the so-called implicit methods have been developed in 31 order to better account for this interaction. 32 In this paper, the applicability of the CV-CF methods is discussed for full face excavation 33 tunneling with a stiff support system. An in-depth comparison between plane-strain closed form 34 solutions and numerical results which properly accounts for the 3D effects at the vicinity of the 35 tunnel face is carried out. The range of application of the different approaches of the CV-CF 36 method is discussed. Finally, some simple empirical formula which can be used in preliminary 37 design for a large range of ground conditions are proposed. 38 39