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Journal Articles

Evaluation of excavation damaged zones (EDZs) in Horonobe Underground Research Laboratory (URL)

Hata, Koji*; Niunoya, Sumio*; Aoyagi, Kazuhei; Miyara, Nobukatsu*

Journal of Rock Mechanics and Geotechnical Engineering, 16(2), p.365 - 378, 2024/02

https://doi.org/10.1016/j.jrmge.2023.05.010

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.

Journal Articles

Evaluation of time lapse behavior of excavation damaged zone by first arrival tomography in Horonobe Underground Research Laboratory

Ozaki, Yusuke; Miyara, Nobukatsu

Proceedings of 14th SEGJ International Symposium (Internet), 4 Pages, 2021/10

https://doi.org/10.1190/segj2021-055.1

The drift excavation damages the intact rock around the drift wall and changes the physical properties there. The damaged domain is called excavation damaged zone (EDZ). The correct estimation of depth and the understanding of time lapse behavior of EDZ is required for the technology of drift closure. In Horonobe Underground Research Laboratory (URL), we repeatedly performed the travel time tomography to investigate the time lapse behavior of EDZ generated in soft sedimentary rock over time. For the analysis of the acquired data for the travel time tomography, we performed numerical simulation and estimated the conceivable change in the arrival time. The results of numerical simulation indicate that the shotcrete on the drift wall has the great impact on the travel time because of its high stiffness whereas the effect of shotcrete fixing the ray path might be the advantage for the monitoring purpose. The analysis of the data acquired at 350 m suggest that the significant change in EDZ that surpasses the observation limit was not recognized.

Journal Articles

Evaluation of excavation damaged zone by optical measurement in Horonobe Underground Research Laboratory

Hata, Koji*; Nyunoya, Sumio*; Aoyagi, Kazuhei; Miyara, Nobukatsu

Doboku Gakkai Rombunshu, F1 (Tonneru Kogaku) (Internet), 77(2), p.I_29 - I_43, 2021/00

https://doi.org/10.2208/jscejte.77.2_I_29

no abstracts in English

JAEA Reports

Long-term monitoring of the stability of the gallery in Horonobe Underground Research Laboratory

Aoyagi, Kazuhei; Sakurai, Akitaka; Miyara, Nobukatsu; Sugita, Yutaka

JAEA-Research 2020-004, 68 Pages, 2020/06

JAEA-Research-2020-004.pdf:6.4MB
JAEA-Research-2020-004-appendix1(DVD-ROM).zip:636.84MB
JAEA-Research-2020-004-appendix2(DVD-ROM).zip:457.72MB
JAEA-Research-2020-004-appendix3(DVD-ROM).zip:595.19MB

In construction and operational phase of a high-level radioactive waste disposal project, it is necessary to monitor on mechanical stability of underground facility for long term. In this research, we measured the displacement of the rock around the gallery and the stress acting on support materials. Furthermore, we investigated the durability of measurement sensor installed in the rock mass and the support material such as concreate lining and steel support. As a result, optical fiber sensor is appropriate for measurement of the displacement of rock mass around the gallery, while it is enough to apply the conventional electric sensor for the measurement of stress acting on the support material in the geological environment (soft rock and low inflow). The result of the measurement in the fault zone in 350 m gallery, show that the stresses acting on both shotcrete and steel arch lib exceeded the value which will cause the instability of the gallery. However, as, we found no crack on the surface of the shotcrete. By observation on the surface of shotcrete, thus, it was concluded that careful observation of shotcrete around that section in addition to the monitoring the measured stress was necessary to continue. In other measurement sections, there was no risk for the instability of the gallery as a result of the investigation of the measurement result.

JAEA Reports

Synthesis report on the R&D for the Horonobe Underground Research Laboratory; Project carried out during fiscal years 2015-2019

Nakayama, Masashi; Saiga, Atsushi; Kimura, Shun; Mochizuki, Akihito; Aoyagi, Kazuhei; Ono, Hirokazu; Miyakawa, Kazuya; Takeda, Masaki; Hayano, Akira; Matsuoka, Toshiyuki; et al.

JAEA-Research 2019-013, 276 Pages, 2020/03

JAEA-Research-2019-013.pdf:18.72MB

The Horonobe Underground Research Laboratory (URL) Project is being pursued by the Japan Atomic Energy Agency (JAEA) to enhance the reliability of relevant disposal technologies for geological disposal of High-level Radioactive Waste through investigations of the deep geological environment within the host sedimentary rock at Horonobe Town in Hokkaido, north Japan. The investigations will be conducted in three phases, namely "Phase 1: Surface based investigations", "Phase 2: Construction phase" (investigations during construction of the underground facilities) and "Phase 3: Operation phase" (research in the underground facilities). According to the research plan described in the 3rd Mid- and Long- term Plan of JAEA, "Near-field performance study", "Demonstration of repository design option", and "Verification of crustal-movement buffering capacity of sedimentary rocks" are important issues of the Horonobe URL Project, and schedule of future research and backfill plans of the project will be decided by the end of 2019 Fiscal Year. The present report summarizes the research and development activities of these 3 important issues carried out during 3rd Medium to Long-term Research Phase.

JAEA Reports

Visualization of fractures in an excavation damaged zone in the Horonobe Underground Research Laboratory, 2 (Joint research)

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.

JAEA Reports

Earthquake observation data collection in the Horonobe Underground Research Laboratory Project (Phase II)

Miyara, Nobukatsu; Matsuoka, Toshiyuki

JAEA-Data/Code 2019-013, 8 Pages, 2020/01

As part of the research and development program on the geological disposal of high-level radioactive waste (HLW), the Horonobe Underground Research Center, a division of the Japan Atomic Energy Agency (JAEA), is implementing the Horonobe Underground Research Laboratory Project (Horonobe URL Project) with the aim at investigating sedimentary rock formations. This data collection is a compilation of Earthquake observation data acquired in the Horonobe Underground Research Project (Phase II).

Journal Articles

A Measurement method of long-term mechanical stability of support and rock mass after the excavation of galleries; Case study in Horonobe Underground Research Center

Aoyagi, Kazuhei; Sakurai, Akitaka; Miyara, Nobukatsu; Sugita, Yutaka; Tanai, Kenji

Shigen, Sozai Koenshu (Internet), 6(2), 7 Pages, 2019/09

no abstracts in English

Journal Articles

The Dynamic response of Horonobe Underground Research Center during the 2018 June 20 earthquake

Sato, Toshinori; Aoyagi, Kazuhei; Miyara, Nobukatsu; Aydan, mer*; Tomiyama, Jun*; Morita, Tatsuri*

Proceedings of 2019 Rock Dynamics Summit in Okinawa (USB Flash Drive), p.640 - 645, 2019/05

An earthquake with a moment magnitude of 4 occurred in June 20, 2018, which is also named as the 2018 June 20 Soya Region earth-quake. The strong motions induced by this earthquake were recorded by the accelerometers installed in the Horonobe URL as well as the Kik-Net and K-Net strong motions networks operated by the National Research Institute for Earth Science and Disaster Prevention of Japan. The authors explain the results of the analyses carried out on the ground amplification and frequency characteristics of the acceleration records at the Horonobe URL and those of the Kik-net strong motion station and the structural effect of the URL on the ground amplification and frequency characteristics. Furthermore, the authors discuss the implications of the results obtained from this study in practice and the safety of the nuclear waste disposal at depth.

Journal Articles

Evolution of the excavation damaged zone around a modelled disposal pit; Case study at the Horonobe Underground Research Laboratory, Japan

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.

Journal Articles

Status of rock dynamics study in Horonobe Underground Research Laboratory, Japan

Sato, Toshinori; Aoyagi, Kazuhei; Matsuzaki, Yoshiteru; Miyara, Nobukatsu; Miyakawa, Kazuya

Rock Dynamics; Experiments, Theories and Applications, p.575 - 580, 2018/06

Rock dynamics is one of key issue for research and development of techniques for safe geological disposal of high-level radioactive waste. Horonobe Underground Research Laboratory (URL) is off-site URL constructed in soft sedimentary rock to the depth of 350m with three shafts and three level experimental galleries. Earthquake-resistant design of underground openings, observation of seismic records and groundwater pressure change due to earthquakes, and excavation disturbed zone experiment have been performed relating to the study of rock dynamics in URL project. This paper shows current status of Horonobe URL project and results of earthquake-resistant design of shafts, observation of seismic records and groundwater pressure change due to the 2011 off the Pacific coast of Tohoku Earthquake.

Journal Articles

Temporal trend in excavation disturbed zone around a modeled disposal pit in Horonobe Underground Research Laboratory

Aoyagi, Kazuhei; Miyara, Nobukatsu; Ishii, Eiichi; Matsuzaki, Yoshiteru

Shigen, Sozai Koenshu (Internet), 5(1), 7 Pages, 2018/03

no abstracts in English

JAEA Reports

Data of geophysical logging based on the deep borehole investigations in the Horonobe Underground Research Laboratory Project (Phase I)

Miyara, Nobukatsu; Matsuoka, Toshiyuki

JAEA-Data/Code 2017-005, 34 Pages, 2017/03

JAEA-Data-Code-2017-005.pdf:5.12MB
JAEA-Data-Code-2017-005-appendix(CD-ROM).zip:27.66MB

Japan Atomic Energy Agency (JAEA) is performing the Horonobe Underground Research Laboratory Project, which includes a scientific study of the deep geological environment as a basis of research and development for geological disposal of high level radioactive wastes (HLW), in order to establish comprehensive techniques for the investigation, analysis and assessment of the deep geological environment in the sedimentary rock. This report integrates geophysical logging data obtained from the deep borehole investigations (HDB-1 HDB-11) conducted in the Horonobe Underground Research Laboratory Project (Phase I).