Facing a major geological hazard for a highway tunnel in the French Alps

摘要

The paper presents a case history of a twin tunnel for a motorway in French Alps, to be excavated in metamorphic rocks, but which had to face to a major soil & water ingress due to an unforeseen paleo-valley filled with sands and gravel's, with high water table. The paper presents the geological data showing the very uneven shape of the paleo-valley and the ground treatments performed to cross the accident zone : bentonite & cement grouting, compaction grouting and jet-grouting (umbrella, face reinforcement, micropiles and reinforcement under the invert). For these jet-grouting works, the paper deals with the design of the project, the FEM calculations performed, the actual progress of the works in the tunnels and the incidence of this geological hazard on the tunnels construction.