Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Hata, Koji*; Niunoya, Sumio*; Aoyagi, Kazuhei; Miyara, Nobukatsu*
Journal of Rock Mechanics and Geotechnical Engineering, 16(2), p.365 - 378, 2024/02
Excavation of underground caverns, such as mountain tunnels and energy-storage caverns, may cause the damages to the surrounding rock as a result of the stress redistribution. In this influenced zone, new cracks and discontinuities are created or propagate in the rock mass. Therefore, it is effective to measure and evaluate the acoustic emission (AE) events generated by the rocks, which is a small elastic vibration, and permeability change. The authors have developed a long-term measurement device that incorporates an optical AE (O-AE) sensor, an optical pore pressure sensor, and an optical temperature sensor in a single multi-optical measurement probe (MOP). Japan Atomic Energy Agency has been conducting R&D activities to enhance the reliability of high-level radioactive waste (HLW) deep geological disposal technology. In a high-level radioactive disposal project, one of the challenges is the development of methods for long-term monitoring of rock mass behavior. Therefore, in January 2014, the long-term measurements of the hydro-mechanical behavior of the rock mass were launched using the developed MOP in the vicinity of 350 m below the surface at the Horonobe Underground Research Center. The measurement results show that AEs occur frequently up to 1.5 m from the wall during excavation. In addition, hydraulic conductivity increased by 2 to 4 orders of magnitude. Elastoplastic analysis revealed that the hydraulic behavior of the rock mass affected the pore pressure fluctuations and caused micro-fractures. Based on this, a conceptual model is developed to represent the excavation damaged zone (EDZ), which contributes to the safe geological disposal of radioactive waste.
Aoyagi, Kazuhei; Chen, Y.*; Ishii, Eiichi; Sakurai, Akitaka; Miyara, Nobukatsu; Ishida, Tsuyoshi*
JAEA-Research 2019-011, 50 Pages, 2020/03
JAEA-Research-2019-011.pdf:3.48MB
In this research, we performed the resin injection experiment at the 350 m Gallery of Horonobe Underground Research Laboratory in order to identify the distribution of fractures induced around the gallery owing to excavation. We also observed the rock cores obtained around the resin injection borehole under ultraviolet light. As a result, the extent of the development of EDZ fracture was 0.9 m from the gallery wall. In the depth within 0.4 m from the gallery wall, the density of the EDZ fracture is higher than the depth more than 0.4 m from the gallery wall. As a result of the analysis on the fracture aperture by image processing, the fractures with a large aperture (1.02 mm in maximum) were observed within 0.3 m from the gallery wall, while the maximum aperture was 0.19 mm in the depth more than 0.3 m from the gallery wall.
Aoyagi, Kazuhei; Chen, Y.*; Ishii, Eiichi; Sakurai, Akitaka; Ishida, Tsuyoshi*
Proceedings of 5th ISRM Young Scholars' Symposium on Rock Mechanics and International Symposium on Rock Engineering for Innovative Future (YSRM 2019 and REIF 2019) (USB Flash Drive), 6 Pages, 2019/12
In the excavation of a repository for high-level radioactive waste (HLW) disposal, it is important to understand the hydro-mechanical characteristics of the Excavation Damaged Zone (EDZ) induced around the gallery because EDZ can lead to the migration pathway of radionuclides. Thus, we performed the resin injection experiment at the 350 m gallery of Horonobe Underground Research Laboratory in Japan to investigate the characteristics of fractures induced around the gallery wall in excavation. In the experiment, we developed a low viscosity resin mixed with a fluorescent substance and injected to the borehole drilled about 1 m in length. After the experiment, we overcored around the injection borehole. The observation on the cut surface of the overcore under ultraviolet light revealed that the fractures were distributed within 0.8 m from the gallery wall. Fractures are interconnected each other in particular within 0.25 m from the niche wall. Furthermore, fractures with large aperture (about 1.0 mm) were developed in that region. These observed results will be fundamental information for understanding of the fracturing process in the EDZ.
Aoyagi, Kazuhei; Tokiwa, Tetsuya*; Sato, Toshinori; Hayano, Akira
Proceedings of 2019 Rock Dynamics Summit in Okinawa (USB Flash Drive), p.682 - 687, 2019/05
In high-level radioactive disposal projects, it is important to investigate the extent of the excavation damaged zone (EDZ) for safety assessment because EDZ can provide a migration pathway for radionuclides from the facility. To investigate the quantitative differences between EDZs formed because of blasting and mechanical excavation, we studied the characteristics of fractures induced by excavation based on fracture mapping performed during shaft sinking (V- and E-Shafts). As a result, it was found that blasting excavation can lead to the formation of a large number of newly created fractures (EDZ fractures) compared with mechanical excavation. In addition, the seismic velocity (P-wave velocity) measured during blasting excavation (E-Shaft) was lower than that measured during mechanical excavation (V-Shaft). Furthermore, we found that the support pattern that reinforces forward rocks to be appropriate for limiting damage to the shaft wall.
Aoyagi, Kazuhei; Ishii, Eiichi
Rock Mechanics and Rock Engineering, 52(2), p.385 - 401, 2019/02
Times Cited Count：16 Percentile：67.51(Engineering, Geological)Excavation of deep underground openings induces permeable fractures around the opening due to stress redistribution. Such a zone is called excavation damaged zone (EDZ). In a high-level radioactive waste disposal project, the EDZ might provide pathways for the migration of radionuclides around the facility. Thus, this study focused on the development of a method for estimating the highest potential hydraulic conductivity in the EDZ around a gallery in the Horonobe Underground Research Laboratory, Japan. Borehole televiewer surveys, rock core observations, and hydraulic tests were undertaken to investigate the extent and magnitude of hydraulic conductivity in the EDZ around the gallery. The observed extent of the EDZ shows good agreement with the EDZ estimated from hydro-mechanical coupling analysis. The measured hydraulic conductivities of the EDZ are within the range of those based on the Mean Stress Index (MSI), which is defined as the ratio of the effective mean stress derived from numerical analyses to the tensile strength of intact rock. Given that the rock mass is relatively homogeneous and artificial damage (e.g., blasting-induced damage) can be neglected, as in the Horonobe Underground Research Laboratory, the MSI model is likely to be applicable in estimating the highest potential hydraulic conductivity in the EDZ.
Aoyagi, Kazuhei; Miyara, Nobukatsu; Ishii, Eiichi; Nakayama, Masashi; Kimura, Shun
Proceedings of 13th SEGJ International Symposium (USB Flash Drive), 5 Pages, 2018/11
The construction of underground facilities induces fractures in the rock mass around the underground voids due to the resultant stress redistribution. This has particular implications for high-level radioactive waste (HLW) disposal projects, where fracture development creates an excavation damaged zone (EDZ) that increases the hydraulic conductivity of the surrounding rock mass and can provide a pathway for the migration of radionuclides from the storage facilities. It is therefore important to understand the long-term evolution of the EDZ and perform a comprehensive HLW disposal risk assessment. An in situ engineered barrier system experiment was conducted in the 350 m gallery at the Horonobe Underground Research Laboratory, Japan, to observe the near-field coupled thermo-hydro-mechanical-chemical (THMC) process in situ and validate coupled THMC models. Here we investigate the evolution of the EDZ around the gallery and model a test pit that was excavated below the floor of the gallery using a series of seismic tomography surveys. There was a significant decrease in the seismic velocity field around the test pit due to its excavation, which became slightly more pronounced over time after the excavation. These seismic results, coupled with hydraulic tests and pore pressure measurements around the pit, indicate that fracture development and the decrease in saturation around the test pit resulted in a decrease in the seismic velocity field after the excavation of the test pit. Furthermore, the increase in saturation around the test pit is a key reason for the increase in the seismic velocity field after the heater test.
Sugita, Yutaka; Aoyagi, Kazuhei; Kubota, Kenji*; Nakata, Eiji*; Oyama, Takahiro*
JAEA-Research 2018-002, 72 Pages, 2018/06
JAEA-Research-2018-002.pdf:6.16MB
In a excavation of shafts and galleries in the deep underground for disposing radioactive waste, an excavation damaged zone (EDZ) is developed around the galleries and shafts owing to the stress redistribution. Since the characteristic changes of the rock mass in the EDZ affects the radionuclides migration behavior, it is important to understand the long-term behavior of the EDZ. Thus, we performed the in situ experiment to investigate the long-term behavior of EDZ as part of the collaborative research between Japan Atomic Energy Agency and Central Research Institute of Electric Power Industry in the 140m gallery in the Horonobe Underground Research Laboratory. In this research, we investigated the extent, mechanism of the change of hydro-mechanical characteristic, and long-term behavior of the EDZ on the basis of the comprehensive estimation of the results of the observation of the drift wall and the various investigations using boreholes such as geological investigation, the seismic and resistivity tomography, hydraulic test, water content monitoring, borehole loading test, convergence measurement, and so on. In addition, we clarified applicability and future tasks of the testing method used in this research for the investigation of the long-term behavior of the EDZ.
Aoyagi, Kazuhei; Chen, Y.*; Sakurai, Akitaka; Ishii, Eiichi; Ishida, Tsuyoshi*
JAEA-Research 2017-014, 49 Pages, 2018/01
JAEA-Research-2017-014.pdf:16.29MB
In this research, we performed the resin injection experiment at the 350 m gallery of the Horonobe Underground Research Laboratory in order to identify the three dimensional distribution of fractures induced around the gallery owing to excavation. To this end, the low viscosity resin mixed with a fluorescent substance was developed and applied to the in situ resin injection experiment. As a result, the resin was successfully penetrated into the fractures around the gallery without disturbing their situation and then fixed within them. After the experiment, the rock cores around the injection borehole were drilled for the observation. The observation under ultraviolet light revealed that the extent of the development of fractures was about 0.9 m into the borehole wall. In addition, the aperture of the fractures distributed within 0.3 m from the gallery wall was ranged 1 to 2 mm, and that distributed from 0.3 to 0.9 m was less than 1 mm. On the other hand, in the borehole televiewer (BTV) survey, only one fracture within 0.2 m from the wall could be detected owing to the resolution of the survey system. Thus, it is expected that the BTV survey underestimate the extent of the development of fractures.
Aoyagi, Kazuhei; Ishii, Eiichi
Shigen, Sozai Koenshu (Internet), 4(2), 7 Pages, 2017/09
no abstracts in English
Aoyagi, Kazuhei; Kubota, Kenji*; Nakata, Eiji*; Suenaga, Hiroshi*; Nohara, Shintaro*
JAEA-Research 2017-004, 91 Pages, 2017/06
JAEA-Research-2017-004.pdf:6.07MB
In this study, we performed seismic tomography, seismic refraction survey, resistivity tomography, and hydraulic tests to investigate the hydro-mechanical property of the excavation damaged zone (EDZ) in the 250 m gallery of the Horonobe Underground Research Laboratory. As a result of seismic tomography, seismic velocity is significantly decreased within 1 m from the gallery wall. The decrease of seismic velocity is related to the density of fracture induced around the gallery wall as a result of the gallery excavation. Thus the extent of the fractures induced by gallery excavation, i.e., EDZ fractures is clarified to be within 1.0 m from the gallery wall. The enhanced hydraulic conductivity was detected within 0.5 to 1.0 m from the gallery wall on the basis of the result of hydraulic tests. This is almost consistent with the extent of the region that seismic velocity is significantly decreased. Therefore, it is estimated that EDZ fractures induced around the gallery leads to the increase of hydraulic conductivity. In addition, the desaturation zone around the gallery is not induced as a result of resistivity tomography. From these results, the hydro-mechanical property of the EDZ is clarified in detail. Also, the in situ tests and evaluation method applied in this study are appropriate to investigate the EDZ in detail.
Aoyagi, Kazuhei; Ishii, Eiichi; Ishida, Tsuyoshi*
Journal of MMIJ, 133(2), p.25 - 33, 2017/02
In the construction of a deep underground facility, the hydromechanical properties of the rock mass around an underground opening are changed significantly due to stress redistribution. This zone is called an excavation damaged zone (EDZ). In high-level radioactive waste disposal, EDZs can provide a shortcut for the escape of radionuclides to the surface environment. Therefore, it is important to develop a method for predicting the detailed characteristics of EDZs. For prediction of the EDZ in the Horonobe Underground Research Laboratory of Japan, we conducted borehole televiewer surveys, rock core analyses, and repeated hydraulic conductivity measurements. We observed that niche excavation resulted in the formation of extension fractures within 0.2 to 1.0 m into the niche wall, i.e., the extent of the EDZ is within 0.2 to 1.0 m into the niche wall. These results are largely consistent with the results of a finite element analysis implemented with the failure criteria considering failure mode. The hydraulic conductivity in the EDZ was increased by 3 to 5 orders of magnitude compared with the outer zone. The hydraulic conductivity in and around the EDZ has not changed significantly in the two years following excavation of the niche. These results show that short-term unloading due to excavation of the niche created a highly permeable EDZ.
Aoyagi, Kazuhei; Ishii, Eiichi
Dai-14-Kai Iwa No Rikigaku Kokunai Shimpojiumu Koen Rombunshu (Internet), 6 Pages, 2017/01
The objective of this research is to investigate the hydro-mechanical properties of excavation damaged zones (EDZs) along the galleries excavated in 250 m and 350 m depths. We conducted hydraulic tests, BTV observations and core analyses. As a result, in the 250 m gallery, the extent of the EDZ was 1.0 m into the gallery wall. The hydraulic conductivity was increased by 2 to 3 orders of magnitudes compared with that of intact rock. On the other hand, in the 350 m gallery, the extent of the EDZ was 0.4 m into the gallery wall; the hydraulic conductivity was increased by 5 orders of magnitudes compared with that of intact rock. We investaged the difference of the characteristics of the EDZs on the basis of competence factor and ductility index. As a result, it was estimated that an extent of an EDZ decreases with decrease of competence factor; a hydraulic conductivity in an EDZ increases with decrease of ductility index.
Hata, Koji*; Niunoya, Sumio*; Aoyagi, Kazuhei
Dai-14-Kai Iwa No Rikigaku Kokunai Shimpojiumu Koen Rombunshu (Internet), 6 Pages, 2017/01
The objective of this research is to investigate the long-term hydro-mechanical behavior of rock mass around the shaft in the Horonobe Underground Research Laboratory (URL). The long-term monitoring has been carried out by optical AE sensors, optical water pressure sensors, and optical temperature sensors below 350m depth of the shaft in the Horonobe URL. From the measurement results, the extent of an excavation damaged zone was 1.5m within the shaft wall. After the excavation, it was observed that the unsaturated zone of the groundwater was spread more than 1.5m within the shaft wall.
Aoyagi, Kazuhei; Tokiwa, Tetsuya*; Fujita, Tomoo
Rock Mechanics and Rock Engineering; From the Past to the Future (EUROCK 2016), p.1023 - 1028, 2016/07
Tokiwa, Tetsuya*; Aoyagi, Kazuhei; Fujita, Tomoo
Rock Mechanics and Rock Engineering; From the Past to the Future (EUROCK 2016), p.901 - 906, 2016/07
Aoyagi, Kazuhei; Ishii, Eiichi; Fujita, Tomoo; Motoshima, Takayuki*
Dai-44-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koenshu (CD-ROM), p.313 - 318, 2016/01
The objective of this research is to investigate the extent and failure mechanism of an Excavation Damaged Zone (EDZ) induced around the East Access Shaft in the Horonobe Underground Research Laboratory. As a result of hydraulic tests, hydraulic conductivity within 2 m from the shaft wall was increased by 1 to 3 orders of magnitude. This result is consistent with the extent of the development of fractures detected by borehole televiewer surveys. Furthermore, the dominant failure mechanism of the fractures around the shaft wall was almost tensile; also these fractures were caused by the short-term excavation-induced unloading.
Hata, Koji*; Niunoya, Sumio*; Aoyagi, Kazuhei; Fujita, Tomoo
Dai-44-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koenshu (CD-ROM), p.319 - 324, 2016/01
Long-term monitoring and EDZ (Excavated Damage Zone) evaluation is carried out by this multi-optical measurement probe in the depth of 350m vertical shaft of Horonobe Underground Research Center project of the Japan Atomic Energy Agency. We have developed a multi-optical measurement probe incorporating an optical AE sensor, an optical water pressure sensor and an optical temperature sensor. Result of the measurement of AE, water pressure and temperature, it was made clear the influence of the shaft excavation. And from the source location analysis, it was found EDZ was less than 1.5m from shaft wall.
Aoyagi, Kazuhei; Tsusaka, Kimikazu*; Nohara, Shintaro*; Kubota, Kenji*; Tokiwa, Tetsuya*; Kondo, Keiji*; Inagaki, Daisuke*
Proceedings of 8th Asian Rock Mechanics Symposium (ARMS-8) (USB Flash Drive), 8 Pages, 2014/10
Hata, Koji*; Niunoya, Sumio*; Matsui, Hiroya; Miyara, Nobukatsu
no journal, ,
no abstracts in English
Oizumi, Ryo*; Kato, Takeshi*; Kiho, Kenzo*; Kuboshima, Koji*; Miyara, Nobukatsu
no journal, ,
no abstracts in English
