Anisotropic Closure in Squeezing Rocks: The Example of Saint-Martin-la-Porte Access Gallery
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ORIGINAL PAPER
Anisotropic Closure in Squeezing Rocks: The Example of Saint-Martin-la-Porte Access Gallery The Manh Vu • Jean Sulem • Didier Subrin Nathalie Monin • Judith Lascols
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Received: 6 April 2012 / Accepted: 11 July 2012 / Published online: 30 October 2012 Ó Springer-Verlag Wien 2012
Abstract In this paper, we analyse the convergence measurements recorded in a gallery excavated in severely squeezing ground. The procedure consists in a preliminary geometrical treatment of the raw data to evaluate the principal axes of deformation by assuming an elliptic deformation of the walls of the gallery. Then the convergence law proposed by Sulem et al. (Int J Rock Mech Min Sci Geomech Abstr 24(3):145–154, 1987a), which is extended to account for anisotropic closure, is fitted on the displacements along the two axes of the obtained ellipse. This procedure is more robust and relevant than fitting the convergence recorded on the most deforming segment or fitting the average value of the convergence along the various segments. An attempt is made to correlate the amount and the direction of anisotropic deformation with the lithology and some geological features described by the dominant discontinuity families. Keywords Tunnel deformation Squeezing ground Anisotropy Convergence measurements Geological structures
T. M. Vu D. Subrin Centre d’E´tudes des Tunnels, Bron, France T. M. Vu J. Sulem (&) UR Navier-CERMES, E´cole des Ponts Paris Tech, IFSTTAR, CNRS, Universite´ Paris-Est, Marne-la-Valle´e, France e-mail: [email protected] N. Monin Lyon-Turin Ferroviaire SAS, Chambe´ry, France J. Lascols Fugro Engineers B.V., The Hague, The Netherlands
1 Introduction As part of the Lyon–Turin railway link project, the excavation of Saint-Martin-la-Porte inclined access gallery has been recently completed. Tunnelling works started in 2003 and were completed in July 2010. The length of the gallery is 2,329 m and has been excavated in a Carboniferous Formation, ‘‘Zone Houille`re Brianc¸onnaise-Unite´ des Encombres’’ which is composed of black schists (45–55 %), sandstones (40–50 %), coal (5 %), clay-like shales and cataclastic rocks (Barla et al. 2011a; Vu 2010; Bonini and Barla 2012). A characteristic feature of the ground observed at the face during excavation is the anisotropic, highly heterogeneous, disrupted and fractured conditions of the rock mass which exhibits a very severe squeezing behaviour according to the classification of Hoek (2001). Squeezing behaviour is characterized by large timedependent and often anisotropic deformations during and well after excavation and may lead to tremendous operational difficulties (see, e.g. Panet 1996). This time dependency is mainly explained by two different phenomena: (a) creep caused by exceeding a limiting shear stress of the rock mass (viscous behaviour or unstable crack propagation) or creep along large scale discontinuities such as bedding and foliation surfaces, joints and faults and (b) consolidation. As summarized in the review paper of Barla (2001), the squeezing
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