ABSTRACT

Hydrogeological risk assessment is an issue of significant importance for tunneling projects in karst regions such as Ligerz safety gallery located in the Bernese Jura, Switzerland. In such conditions, major changes in the project plan might be required either in advance or during the construction. Hydrogeological pre-studies revealed a significant probability of karst occurrences with discharge rates reaching up to 10 m3/s. Risk mitigation measures were necessary to define security procedures to avoid large water inrush. The KarstALEA method was applied to identify sections with a high probability of karst occurrence and to characterize the associated problems. Finally, the combination of a hydraulic model of the karst flows with real-time measurements, make possible to estimate the expected inrush discharge and to define the alert threshold to temporary stop the excavation during the most critical situations.