ABSTRACT
This article presents the design studies for the Le Locle tunnel, located in the canton of Neuchâtel (Switzerland). It is designed to bypass the town of Le Locle to the north, relieving the city center of its heavy traffic. In the east portal area, because of a rock mass with poor geotechnical characteristics, the traditional excavation method, in sequential sections with the installation of presupports (umbrella and face bolting), is preferred. In addition, in this first part of the tunnel, there is a very sensitive structure consisting of the CFF Railway line. In order to justify the construction choices, design the various supports and assess the impact on the railway line, complex numerical simulations were required in the design phase. They permit simulating the phasing of the works, the variable-section excavation geometry and the various presupport and support elements.
