ABSTRACT
The construction of the Saint-Martin-La-Porte 4 works has been completed since October 3, 2022. This is the first worksite for the excavation of the Lyon-Turin rail base tunnel: 10.4 km were excavated in the final section on the south pipe axis of the project. This work was carried out in advance of the overall project, with the aim of verifying its feasibility. Located under a large overburden, the crews excavate in the geological unit of the Houiller Briançonnais consisting of arenaceous and black shales with coal levels, the most challenging geotechnical environment of the project, and characterized by strong convergence. 7 years of work were necessary to excavate 9 km of tunnel with TBM and more than 3 km in conventional method. The last two years have been particularly dedicated to the excavation in conventional method of 1.4 km in the geological zone of the Houiller Briançonnais; an experimental crossing in heterogeneous geology, with squeezing rock (convergence > 1 m in diameter), and at significant depth (overburden between 600 and 650 m in part 3b). These difficulties have allowed the Contractors group to reinvent itself by developing innovative methods for excavation and support. This article proposes to carry out the synthesis of this atypical context, of the forecasts, excavations, surveys, monitoring of deformations, back-analysis and model adjustment, evolution of methods and finally a planning synthesis.
