Evaluating face stability in mountain tunnel excavation by inclination monitoring at the tunnel crown - Atoda tunnel case study

The authors have been developing a prediction method for changes of ground stiffness ahead of a tunnel face by monitoring inclination at the tunnel crown (along the face advance axis). During the Atoda tunnel construction project, inclination monitoring was conducted at measurement intervals of 10 m. This is the first tunneling project practically using the proposed method throughout the excavation length. There is used a newly developed tilt sensor equipped with a Low-Power and Wide-Area (LPWA) wireless communication system that collects inclination data and transmits it to a data gateway automatically. During excavation work zones of weathered and fractured tuff breccia were recognized; face instability and partial collapse were experienced at those locations, though tunnel deformation was generally no more than 10 mm. Inclination values had a tendency to decrease in tunnel advance direction before the face encountered the soft/weak weathered rock, verifying the effectiveness of the method for monitoring tunnel stability and safety.