Non-destructive testing of fired tunnel walls:: the Mont-Blanc Tunnel case study

The investigation of fired tunnel walls typically relies on visual inspection and a comprehensive study of core samples. Visual inspection is limited to surface diagnosis, while core samples only provide a detailed image of the damaged zone at a single point. In order to gain an extensive view of the entire depth of the damaged zone as well as specific material properties, both the seismic refraction method and ground-penetrating radar investigation may be carried out. In the case of the Mont-Blanc Tunnel, these non-destructive methods have been tested in three zones: heavily damaged, moderately damaged, and sound. On the radargrams generated, several layers can be roughly identified; seismic refraction then confirms and characterises the existence of layers with contrasting mechanical properties. (C) 2003 Elsevier Science Ltd. All rights reserved.