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  Definition of Confining Pressure for Large Diameter EPB Tunnels in the Parisian Basin

  Mechanized tunnelling in dense urban environments using earth pressure balance (EPB) machines requires the application of a confining pressure at the cutter head and around the machine’s shield. This pressure is necessary to not only ensure the stability of the tunnel face but also to limit surface settlements and mitigate the impact of tunnelling on nearby buildings and infrastructure. The level of deconfinement (λ) is a key parameter in the determination of confining pressures when using the finite element method. This paper compares the method of determining λ typically used in the Paris region with actual levels of deconfinement observed during the execution of three major tunnelling projects in the Parisian Basin in France. The paper subsequently concludes on the need to integrate industry experience and observational principles to optimise the assumptions relating to EPB tunnel deconfinement in Paris. The reference projects used in this comparison are the Tramway T6 (Lot 1), the extension of the Paris metro line 12 (Lots 1 and 2), and the northern extension of Paris metro line 14 (Lot 1).

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