A considerable number of in situ permeability tests in flysch are processed to a depth of 120m with a good spatial distribution. The distribution of permeability values for the different litho-types of this formation, their comparison and their decrease with depth is discussed. The depth where a permeability of 3 to 5×10 -7 m/sec can be retained (the limit of a reasonable grouting under a high dam) may be twofold if the geological history of the formation could not contain a compressional tectonic process. This depth may reach 100m in some cases. The differences in the mean values of permeability among the various litho-types are minor, while the presence of siltstones, always present although with varied participation, dramatically controls the global permeability.
When designing and constructing a tunnel in an urban setting with the use of a closed face Tunnel Boring Machine (TBM), the objective is to ensure both the tunnel face stability and the control of induced ground deformations within predefined, acceptable limits. Unless the exerted active face pressure will match the in situ ground stresses, there will be ground deformations taking place in the advance core, i.e., face extrusion and pre‐convergence, resulting in settlements or heave for active pressure lower or higher than the in situ stresses, respectively. This article presents the validation through finite element method (FEM) of an analytical methodology that can be applied on soft ground urban tunnels to assess the level of active face support to be considered in numerical analysis, to ensure elastic relaxation in the advance core and thus effective ground deformation control. The methodology combines the classic Anagnostou and Kovari method with the Convergence–Confinement method for face support proposed by Aristaghes and Autuori. In the current article, the methodology is described in detail and subsequently validated through three‐dimensional FEM analyses. The article concludes with a discussion on the results and the applicability range of the methodology.
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