The face stability of slurry-shield-driven tunnels

Tunnelling and Underground Space Technology - TUNN UNDERGR SPACE TECHNOL 01/1994; 9(2):165-174. DOI: 10.1016/0886-7798(94)90028-0

ABSTRACT During the excavation of a tunnel through soft water-bearing ground, a temporary support is often required to maintain the stability of the working face. In a slurry shield, this support is provided by a pressurized mixture of bentonite and water. Slurry-shield tunnelling has been applied successfully worldwide in recent years. Under extremely unfavorable geological conditions, however, face instabilities may occur. This paper aims at a better understanding of the mechanics of face failure when using a bentonite slurry support. The complex interrelations between the various parameters (shear strength and ground permeability, suspension parameters, slurry pressure, geometric data of the tunnel, safety factor) are studied. Attention is paid to the time-dependent effects associated with the gradual infiltration of slurry into the ground ahead of the tunnel. Related topics, such as the stand-up time, soil properties and the effect of advance rate, are discussed quantitatively.RésuméLe creusement d'un tunnel dans un terrain meuble nécessite souvent un soutènement temporaire afin de stabiliser le front de taille. Dans le cas d'un bouclier à boue, cette pression de stabilisation est réalisée par un mélange de bentonite et d'eau sous pression. Durant ces dernières années, grâce à une évolution technologique importante, l'utilisation de boucliers à boue pour la réalisation d'ouvrages souterrains a convu un succés mondial. Pourtant, face à des conditions géologiques extrêmement défavorables, des problèmes majeurs de stabilité du front de taille peuvent se présenter. L'article présent a pour objectif d'améliorer la compréhension de la mécanique de la rupture du front de taille pour le cas d'un front stabilisé par de la boue à base de bentonite. On étudie les relations complexes entre les différents paramètres (résistance au cisaillemment et perméabilité du sol, pression de boue, données géométriques du tunnel, coefficient de sécurité) en tenant compte des effets transitoires dûs à l'infiltration progressive de la boue dans le sol en avant de l'avancement. En outre, d'autres sujets comme le temps pendant lequel le front de taille reste stable ou l'influence de la vitesse d'avancement sont discutés quantitativement.

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