Within the Saint-Martin-La-Porte access gallery project, a comprehensive monitoring progamme was implemented in order to explore its extreme squeezing behavior. This paper presents a comprehensive analysis of the geotechnical data, including convergence and extensometric measurements, face extrusion measurements, stress measurements in the lining. The strain distribution in the rock mass around the tunnel and ahead the face and the stress distribution in the lining are evaluated in different sections. Emphasis is put on the comparison of the anisotropic response observed in the various measurements. An identification of quasi homogeneous zones with similar response can be obtained from a detailed study of the deformation data of the ground and of the support.
During the excavation of Saint-Martin-La-Porte (SMLP) access gallery, extreme squeezing conditions occurred when the tunnel encountered the Carboniferous Formation, exhibiting strong time-dependent and highly anisotropic convergence of cross-section. This squeezing behavior has been analyzed in recent studies emphasizing the time-dependent behavior of the rock mass within the frame of viscoplasticity (Barla et al. 2007, 2011) and damage mechanics (Ordaz 2008).The anisotropic behavior of rock mass is further explored in this paper.
The Lyon-Turin Rail Link is a high speed railway line mixed passengers and freight through the Alps between Italy and France. The main work between two countries is a base-tunnel of 57 km long. At present, three access galleries have been completed. The first access gallery from the French portal, the SMLP access gallery, was excavated between March 2003 and the end of 2010, with a design length of 2329m and an excavated profile of 77m2 to 125m2 (for a final internal profile of 54m2 to 63m2).
The section of the access gallery is characterized by the overlapping of the "Houillère Briançonnaise|" zone on the "Sub-briançonnaise" zone, originating a contact marked by Triassic formations (gypsum and anhydrite), called "Front du Houiller". In particular the tunnel crosses the "Productive Carboniferous Formation" (Encombres Unit) which is characterized by a predominance of schists and coals over sandstones. Also present is the "Sterile Carboniferous Formation", a facies consisting of alternating sandstones and black schist, where the sandstone layers prevail (Bonini and Barla, 2012). These formations, usually appearing without continuity and in a highly disturbed structure, result in the very severe squeezing condition which is observed with the following typical phenomena (Fig. 1):
