Evaluation of temporal changes in fracture transmissivity in an excavation damaged zone after backfilling a gallery excavated in mudstone

Aoyagi, Kazuhei; Ishii, Eiichi

Environmental Earth Sciences, 83(3), p.98_1 - 98_15, 2024/02

https://doi.org/10.1007/s12665-023-11416-x

The long-term geological disposal of high-level radioactive waste relies on predictions of future changes in a disposal facility's hydro-mechanical characteristics to assess potential leakage through fractures in the excavation damaged zone (EDZ) after backfilling the facility. This study evaluated the transmissivity of EDZ fractures using in situ hydraulic tests around the area of a full-scale, experimental, engineered barrier system in the Horonobe Underground Research Laboratory, Hokkaido, Japan. After their installation, the buffer blocks swelled, altering the stresses within the EDZ fractures. The effects of these changing stresses on the fractures' transmissivity were assessed over a period of 4 years. The transmissivity continuously decreased in this period to about 41% of its value measured prior to the swelling. Using the Barton-Bandis normal-stress-dependent fracture-closure model, the decrease in transmissivity is quantitatively attributed to closure of the EDZ fractures, which was caused by the swelling pressure increasing up to 0.88 MPa. Evidence of fracture closure came from seismic tomography surveying, which revealed a slight increase in seismic velocity in the study area with increasing swelling pressure. The results show that EDZ fractures were closed by swelling of the full-scale buffer material. They also demonstrate the applicability of the Barton-Bandis model to preliminary estimation of the long-term transmissivity of EDZ fractures in facilities for the geological disposal of radioactive waste.

Evaluation of the excavation disturbed zone of sedimentary rock in the Horonobe Underground Research Laboratory

Kubota, Kenji*; Aoyagi, Kazuhei; Sugita, Yutaka

Proceedings of 2019 Rock Dynamics Summit in Okinawa (USB Flash Drive), p.729 - 733, 2019/05

During the excavation of shafts and galleries in the deep subsurface for disposing of high-level radioactive waste, an excavation disturbed zone (EdZ) or excavation damaged zone (EDZ) is developed around the shafts and galleries. Such zones could influence the transfer behavior of radioactive nuclides, and it is therefore important to understand the behavior of the EdZ or EDZ. We performed in situ experiments before, during, and after gallery excavation in galleries of 140 and 250 m in depth in an area of soft sedimentary rock in Japan. The results demonstrate that the extent of fractures induced by the gallery excavation related with EDZ was confined to about 0.45 m from the gallery wall in the 140 m gallery and to about 1 m from the gallery wall in the 250 m gallery. The extent of the unsaturated zone related with EdZ was about 1 m in the 140 m gallery, but an unsaturated zone did not appear in the 250 m gallery.

A Study on the hydro-mechanical behavior in the excavation damaged zone in shaft sinking at the Horonobe Underground Research Laboratory

Aoyagi, Kazuhei; Sakurai, Akitaka; Tanai, Kenji

Dai-46-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koenshu (CD-ROM), p.142 - 147, 2019/01

This research presents the hydro-mechanical behavior of EDZ in shaft sinking in the Horonobe underground Research Laboratory on the basis of the results of in situ hydraulic tests, acoustic emission (AE) measurements, and hydro-mechanical coupling numerical analysis. The AE sources were distributed within 1.5 m into the shaft wall; and hydraulic conductivity in the EDZ is 2 to 4 orders of magnitudes higher than that in no fractured area. On the other hand, on the basis of the result of numerical analysis, the maximum extent of the EDZ is 1.5 m into the gallery wall. This result is almost consistent with the trend of acoustic emission measurement and hydraulic test.

Development of the observational construction technology in the Horonobe Underground Research Laboratory

Aoyagi, Kazuhei; Nago, Makito*

Jiban Kogakkai-Shi, 65(8), p.12 - 15, 2017/08

In this paper, we described the development of the supporting tool of observational construction of the underground research laboratory, and the monitoring result of hydro-mechanical properties around the gallery wall. As an observational construction tool, we developed a "3D geological structure/construction data visualization system". The geological data, measurement data, construction data, and prediction analysis results are visualized and integrated comprehensively as the construction proceeds. The planned support pattern was examined according to the visualized data. In addition, the Excavation Damaged Zone (EDZ) was extended within 1.0 m from the gallery wall. In this area, hydraulic conductivity was enhanced. However, the extent of the EDZ was not enlarged along with time; the stability of the support was also confirmed on the basis of the measurement of stress in the shotcrete. Integrating these results the observational construction considering the development of an EDZ can be established. This technology will have an important role in geological disposal of high-level radioactive waste.

Excavation of shafts and research galleries at the Mizunami Underground Research Laboratory (construction work of MIU part V); Construction progress report, fiscal year 2012-2013

Geoscience Facility Construction Section, Tono Geoscience Center

JAEA-Review 2016-002, 116 Pages, 2016/06

JAEA-Review-2016-002.pdf:62.4MB

This progress report presents an outline compilation of construction activities, primary tasks performed, construction progress and safety patrol report, in Fiscal Year 2012-2013. The outline of construction activities is a summary based on the scope of work planned in 2012-2013: the main activities are based on the Tono Geoscience Center weekly reports; and the construction progress is based on the planned and actual schedules. The safety patrol report is based on defects recording by the safety manager of the Geoscience Facility Construction Section.

Progress of construction work excavation of shafts and research galleries

Construction Department; Tono Geoscience Center, Sector of Decommissioning and Radioactive Waste Management; Horonobe Underground Research Center, Sector of Decommissioning and Radioactive Waste Management

JAEA-Technology 2015-034, 411 Pages, 2016/03

JAEA-Technology-2015-034.pdf:103.07MB

This report presents the results of shaft and gallery excavation performed focusing on crystalline rock (Mizunami) and sedimentary rock (Horonobe) from the point of view of construction technologies applied and the information obtained at respective construction stages, which is required for construction designing Facility construction in general, its goal is to build the facilities and the general and accrual designs are made based on the specific construction plan, while the construction of shafts and research galleries is being conducted based on the research plan. This construction is performed in the deep underground where significant uncertainties exit, for instance, it is difficult to obtain the precision information from preliminary investigation, construction work is inextricability liked to the stepwise research, and this very long-term construction period is likely to be receiving restrictions concerning environmental and social interests. Therefore, there are a number of conditions can not to be predicted at the initial design stage. Timely and appropriate actions will be taken to deal with these particular conditions, such as changing on design due to the revision of the research and construction plan while conducting excavation construction. In the series of construction activities: from input (i.e. construction conditions) to completion of the construction under the particular conditions, we summarize the experiences obtained at respective construction stages as the important information to transfer the technology to the similar construction in the future. This report describes the general consideration and summary of chapters at the beginning, and introduces the construction activities performed at each rock series.

None

; ; *

JNC TY7430 2000-001, 57 Pages, 2000/03

JNC-TY7430-2000-001.pdf:2.17MB

no abstracts in English

Design research about geological disposal facility (II)

Horita, M.*; *; Okutsu, Kazuo*; Yamamoto, Takuya*; Amemiya, Kiyoshi*

JNC TJ8400 2000-022, 303 Pages, 2000/02

JNC-TJ8400-2000-022.pdf:10.42MB

This report gives supplementary information and discussions on issues of the high-level waste geological disposal study. The following subjects are discussed ; (1)Evaluation of the effects of coefficient of lateral pressure to the specifications of disposal facilities (2)Functional development of remote operational machinery (3)Arrangement of basic data on cost estimation for disposal (4)Understanding of engineering countermeasures to potential phenomena deep under the ground (5)Selection of construction technologies (6)Establishment of the disposal concept under the coasts. For the coefficient of lateral pressure equal to 2, the cross section of disposal drift, the disposal drift spacing, the waste package pitch in the disposal drift and the specification of supporting system are designed. They are compared with those for the case of coefficient of lateral pressure equal to 1. In the case of coefficient of lateral pressure equal to 2, total length of drifts is 1.5 times, and total excavation volume is 1.8 times larger than later case. For the sealing, transportation and emplacement equipment for waste, technology of the fundamental function, remote operation, accidental events and countermeasures are discussed. The plan for developments on those items is proposed. The item of the cost for the construction, operation, and backfilling are discussed. The surface facilities, and, worker arrangement plan are proposed. For the potential phenomena encountered deep under the ground, the countermeasures are investigated form the construction experience, and the future research subjects are discussed for the underground research laboratory. For the construction technologies, the experience of construction management for the tunnel is investigated, and, the research subjects are proposed. For the disposal concept under coasts, rock condition, design condition, construction management, and quality control are compared with the disposal concept under the ground. The ...

None

*; *

JNC TJ7400 2000-001, 79 Pages, 2000/02

JNC-TJ7400-2000-001.pdf:3.07MB

no abstracts in English

Study on construction technology for repository

Tanai, Kenji; Iwasa, Kengo; Hasegawa, Hiroshi; Miura, K.*; Okutsu, Kazuo*; Kobayashi, Masaaki*

JNC TN8400 99-046, 177 Pages, 1999/11

JNC-TN8400-99-046.pdf:6.03MB

For the construction of underground facilities comprising access tunnels, connecting tunnels, main tunnels and disposal tunnels, a large number of tunnels will be excavated in deep rock formations. These excavations will extend hundreds kilometers in total length. Therefore, special attention must be paid, to transporting large volume of debris, ventilation, emergency escape routes in case of accident, and other factors. In addition, special attention must also paid to potential accidents which might in underground excavations, including unstable facing phenomena (such as collapse and swelling of facing at weak layer sections), spring water flow resulting collapse of rock, gas eruption, and rock burst. While considering these factors to be emphasized during the construction of geological disposal facilities, the investigation reviewed the existing working methods on individual construction technologies of access tunnels, main tunnels, connecting tunnels, disposal tunnels, and disposal pit, based on the recognition that the present state deals with a wide range of geological environments, and conducted investigation about the construction methods for each tunnel on the basis current technologies, and described the outline of these methods. Furthermore, for the items to be particulaly emphasized on site characterization koko and siting data such as ground pressure and spring water, the investigation reviewed the current countermeasure works, and made survey on the phenomena appeared during actual tunnel construction works and their countermeasres, and carried out a study on effectiveness of these countermeasures. This constructing of disposal site in deep geological formations is basically possible by applying, or confirming, current excavation technologies for tunnels and underground facilities, A systematic construction system combines separate technologies relating to construction, (excavation technology, tunnel support work method, etc.). Such systems ...