Project Management, Design and Construction for Operational Sites CO6 and CO7
The S2IP consortium, comprising Setec tpi (lead contractor), Systra, Italferr and Pini Swiss Engineers, has won the tender for project management of Operational Worksites CO6 and CO7, as part of the TELT (Lyon-Turin Euralpin Tunnel) project.
These works involve the excavation of the central section of the base tunnel between KM 6+760 and KM 29+900 (a distance of 23 km). They also include the completion of works excavated as part of the SMP4 reconnaissance works: this involves connecting the Saint-Martin-la-Porte and La Praz access shafts to the southern tunnel tube.
Terrasol is specifically addressing the issue of delayed behaviour (squeezing) of coal-bearing shales as the tunnel front passes through the Briançon coal seam. In this context, we have had to analyse the large volume of data collected throughout the excavation of the exploratory tunnels in the coal seam.
Following an initial phase of familiarising ourselves with the work carried out and conducting a detailed analysis of the data collected (geology, in-situ measurements, monitoring, etc.), we were able to analytically assess the response of the rock mass at the base tunnel alignment. In a second phase, the mechanical and delayed behaviour of the rock mass was modelled using 2D and 3D numerical retro-analysis studies in FLAC. The resulting numerical model provided a satisfactory approximation of the rock mass response observed during the excavation of SMP4 and justified the support profiles and the final lining design for a 120-year service life.
The main challenges of this project were the very tight deadlines (less than 5 months), the large volume of data collected over more than 10 years, and the intrinsic complexity of the project. The retro-analysis enabled the entire set of measurements (convergences, convergence rates, extrusions, etc.) to be calibrated using the same behavioural model.
Since 2023, Terrasol has been providing geotechnical monitoring of the works with four engineers on site.
Partners
SETEC TPI
