Evaluation of EDZ around highly stressed rock cavern by AE measurements

In highly stressed rock, the stress-induced cracks are often developed by the excavation of caverns, and EDZ (Excavation Disturbed Zone) will be formed around the caverns. The monitoring and control of EDZ is the one of the most important required technology for the design of caverns such as the high-level radioactive waste repository. Thus the authors are developing the effective design and construction system for underground caverns based on the monitoring of EDZ using AE (Acoustic Emission) that sensitively detects the generation of the stress-induced cracks. In this study, the field measurements of the EDZ, which is developed around the actual large underground cavern in highly stressed rock, is conducted in accordance with the progress of the excavations. The behaviors of AE parameters are compared with the behaviors of stress and displacement. Furthermore, DEM simulation of the bonded particles model of the cavern is carried out using the in-situ rock deformability and strength, and initial rock stress, which are obtained from in-situ tests. The result of the simulation shows good agreement with the actual measurement results on rock stress, crack initiation, etc. As the result, it is clarified that the behavior of AE parameters gives us the very good information on the state of fracturing along the stress path, and this realizes the stress-based observational design and construction system. Further it is also clarified DEM simulation using bonded particle model is a powerful tool to predict the stress change and fracturing.