The development of thrust and bending moment in tunnel liners during face advance, is strictly related to the three dimensional nature of the tunnelling problem. Simplified two dimensional analyses can however be used in design, provided that appropriate correction factors are applied. Rock anisotropy also affects the tunnel"s near face behaviour. and the loads developing in the support. Based on· true three dimensional finite element analyses, correction factors are provided to account for near face behaviour if a simplified two dimensional approach is used. Furthermore the effects of rock anisotropy on thrust and bending moment induced in the liner are discussed.
Le developpement des forces de compression et des moments de flexion dans un revêtement d"un tunnel pendant l"avancement de la face est en relation directe avec la nature tridimensionnelle du problème. Des analyses bidimensionnelles simplifiees peuvent être utilisees pour le design, à condition que des fact.eurs de correct.ion appropries soient appliques. L"anisotropie des roches influence aussi le comportement à la proximite de la face et le developpement des charges dans le revêtement. Sur la base d"analyses tridimensionnelles aux elements finis, des facteurs de correction sont foumis pour tenir compte du comportement à la proximite de la face, dans le cadre d"un approche bidimensionnel. De plus, une discussion des effets de, 1"anisotropie de. roches sur les forces de compression et les moments de flexion induits dans le"revitement, est presentee dans cet article.
Die Erzeugung von Druckbeanspruchungen und Biegemomenten in der Nahe der Ortsbrust iat durch die dreidimensionale Natur des Problems bedingt. Vereinfachte zweidimensionale Analysen können allerdings bei der Bemessung im Zusammenhang mit Verbesserungsfaktoren angewand werden. Die Felsanisotropie beinfluβt das Verhalten des Tunnels in der Nahe der Ortsboriut und die Belastung des Einbaus. Verbesserungsfaktoren fuer zweidimensionale Analysen sind hier auf der Grundlage einer dreidimensionaler Untersuchung hergeleitet. Der Emfluβ von Felaaniaotropie auf die Druckrafte und die Biegemomente wird diskutiert.
Primary support is usually placed behind the tunnel face in order to prevent instability during the excavation process. In modern tunnelling, the importance of this support is emphasized as it provides confinement to the surrounding ground thereby preventing loosening and strength loss. During excavation the liner attracts some load, depending on its stiffness relative to the ground and the installation procedure. Rock anisotropy also affects the tunnel"s near face behavior and therefore can be a dominant factor for load development in the liner during face advance. The prediction. of these loads is a primary concern for the designer and it is strictly related to the three dimensional nature of the tunneling problem. Simplified two dimensional solutions can however be used in design, provided that appropriate correction factors (1.e., established by a truly three dimensional approach) are applied.
Simplified methods to account" for support installation delay associated with near face effects within the frame of a two dimensional approach were developed by several authors (e,g., Panet, 1976; Laabmayr and Swoboda, 1978; Sakurai, 1978). An extensive study by axisymmetric finite element analyses was carried out by Schwartz and Einstein (1980) in order to investigate the effect of delay.
