An investigation of the excavation damaged zone at the KAERI underground research tunnel

The disturbance of a rock due to a blasting impact or stress redistribution can significantly influence the overall performance of an underground excavation. In order to investigate the characteristics of the EDZ (Excavation Damaged Zone) developed during the construction of the KAERI underground research tunnel in Korea (KURT), which is an underground research tunnel for a Korean high-level radioactive waste disposal program, various in situ and laboratory tests were carried out. A Goodman jack test showed that the deformation modules were influenced by a blasting to a depth of 1.5–2 m. With empirical equations, the EDZ could be predicted as 0.3–2.3 m. The average RQD from the rock cores at 0–2 m, where the blasting impact was significant, was 17% lower than that from the deeper regions. From the laboratory tests, the EDZ size could be estimated to be around 0.9–1.5 m. The elastic modules in the EDZ were decreased by about 56%. From a borehole radar reflection survey and a subtracting technique, it was possible to detect the new reflectors generated by a tunnel blasting. By using the determined EDZ size and the properties from the laboratory and in situ tests, a sensitivity analysis was performed. From the sensitivity analysis with seven parameters, it was possible to determine that the in situ stress ratio, Young’s modules, and EDZ size were the three main parameters.