[en] This study aimes to investigate the disturbed zone around the drift excavated in the sedimentary rock formation and to evaluate the accuracy, reliability and effectiveness of existing techniques for excavation, measurement and analysis for the use of the repository construction. For this purpose, a drift (2.5x2.5m, L=30m) was excavated by NATM. Rock mass displacement, rock bolt stress, permeability and pore water pressure were measured in and around the drift. Using this drift as measuring drift, a test drift (3.0x3.0m, L=20m) was excavated parallel to the measuring drift. As the supporting system of this drift only rock bolting was employed. In-situ measurement of rock displacement, elastic wave velocity, permeability and initial stress have been carried out. These results were compared with the predicted results to investigate the effectiveness of the existing evaluation techniques. Laboratory test results and geological mapping data were also used to understand the rock mass behavior and the disturbed zone around drift. These investigations revealed that low velocity zone of elastic wave was generated around the drift, and in the zone, permeability decreased and displacement increased. Rock mass movement was predicted roughly by numerical analysis based on the laboratory test results. And detailed numerical analysis considering the initial stress data and disturbed zone around the drift, provided good simulation of rock mass movement. (J.P.N.)

[en] Japan Atomic Energy Agency (JAEA) and its predecessors have been conducting an extensive geoscientific research program since the 1970's in order to contribute to the formation of a firm scientific and technological basis for the geological disposal of high level radioactive waste in Japan. As a part of this program, in situ experiments have been performed at the Tono Mine in soft sedimentary rocks and at the Kamaishi Mine in hard crystalline rocks. An experiment on excavation disturbance has been one of these experiments and has revealed the extent and properties of the excavation disturbed zone (EDZ) and the applicability of available measurement methods. It is suggested that mechanical excavation and controlled excavation have reduced excavation damage of the rock mass around a drift, although some improvements in the currently available methods for measuring and simulating the EDZ are essential to understand excavation disturbance in more detail. JAEA is now promoting two underground research laboratory projects in Japan; the Mizunami Underground Research Laboratory (MIU) project for crystalline rocks and the Horonobe Underground Research Laboratory (Horonobe URL) project for sedimentary rocks. From a rock mechanical point of view, the major interest in these projects will be paid to failure phenomenon deep underground, rock stress estimation at larger scales and long-term physical stability of underground structure. These projects are open for international collaboration. (author)

[en] Power Reactor and Nuclear Fuel Development Corp. has tested inplace and heap leaching methods considered to be the means to efficiently and economically recover useful metals from low grade ores in developing uranium mines. It has once considered to try heap leaching test in Ningyo pass mines, but re-arranged the plan in which it will first develop the vast leaching to use leaching vats to accumulate the data and experience, then the heap leaching, from the viewpoint of environmental preservation and extraction maximum. Until December, 1980, approximately 6,000 t of crude ores were tested. The leaching test process is composed of five sub-processes of filling, leaching, washing, neutralization and carrying-out. Then the summary of the vast leaching facility is described, following the process flow. In the test results in the fiscal year of 1980, the first circulation days in leaching process are considered as 8 to 10 days, and in the following circulation, 5 days, and the amount of sulfuric acid required was estimated as 20 to 35 kg/t-ore. The relation of the change of uranium concentration expressed logarithmically to the amount of water in washing process was approximately linear. Though the recovery rate was about 95% in the ion exchange process test because the result includes the test run data, it will be 99% or more in steady operation. (Wakatsuki, Y.)

[en] One of the important issues to be studied by in situ experiments is how to identify and model excavation-disturbed zones (EDZ). Rock properties such as permeability and deformability in the EDZs are possibly changed from the original properties. It is necessary to understand the EDZs for assessing the performance of the geological disposal system for high level waste. The objectives of the studies on excavation disturbance are to identify rock properties and the extension of EDZs, and to understand the mechanism of rock mass response to excavation works. For these objectives, it is necessary to develop the methods of measuring and modeling EDZs. Power Reactor and Nuclear Fuel Development Corporation has carried out the in situ experiments on excavation disturbance in Tono Mine which is the site of soft sedimentary rocks and in Kamaishi Mine which is the site of granitic rocks. The studies in Tono Mine and Kamaishi Mine are reported. The numerical analysis by FEM can simulate the measured variation of rock stress and ground displacement. The size of EDZs was estimated to be 1 to 2 m from excavation surfaces. Fracture, stress redistribution and undersaturation changed rock properties. (K.I.)

[en] In-Place Leaching Technology Development has been performed to estimate the projects at exploratory stage in foreign countries. Mainly, we researched the method in order to determine the operating conditions when uranium deposits are developed by the in-place leaching method. For the purpose of comprehending the hydraulic properties and the characteristics of material transportation, several kinds of investigation were carried out at the experiment site located in the southeast part of Tono Uranium Deposit. As the investigations of the hydraulic properties, we performed several sorts of experiments utilizing boreholes and cores, and we constructed and validated the hydraulic flow model of the experiment site. As a result of the work, we obtained a piece of information which will be the input data of the conceptional computer program which could determine the operating conditions for in-place leaching method. (author)

[en] The Mizunami Underground Research Laboratory (MIU) is planned to be constructed at the research site of JNC in Mizunami, Gifu prefecture. A wide range of geoscientific research and development activities which have been performed in and around the Tono mine for these years, is planned to extend in the laboratory. The MIU consists of surface and underground facilities down to a depth of about 1,000 meters. This report describes the overall layout and the basic construction method of the underground facility, including the composition of the overall research program which is necessary to design the underground facility and to select its construction method. (author)

[en] In-place Leaching Technology Development has been performed to estimate the projects at exploratory stage in foreign countries. Mainly, we researched the method in order to determine the operating conditions when uranium deposits are developed by the in-place leaching method. For the purpose of comprehending the hydraulic properties and the characteristics of material transportation, several kinds of investigations were carried out at the experiment site located in the southeast part of Tono Uranium Deposit. As the investigations of the characteristics of material transportation, we tried to fit the measured values obtained by the tracer test between two boreholes to the values calculated by two analytical methods; Gelhar's method and computer simulation method using the two dimensional finite element code. We obtained the result that longitudinal dispersivity is 3.5 m and effective porosity is 4.5 percent by the Gelhar's method or below 10 percent by the computer simulation method. (author)

[en] Excavation of an underground drift disturbs the rock mass around the opening by each of the following processes: Fracturing in the vicinity of opening induced by the excavation work and stress concentration. Changes in the apertures of existing fractures due to stress redistribution. Changes in water pressure around the opening due to water inflow and chemical changes due to the increased oxygen supply to the rock and such phenomena as degassing of groundwater. All of these mechanical, hydrological, and chemical changes to the rock mass are termed excavation disturbance and the affected area is called the 'Excavation Disturbed Zone (EDZ)'. The portion of the EDZ in which the rock mass is fractured due to excavation is called the Excavation Damaged Zone'. This experiment is focused on the mechanical and hydrological property changes caused by excavation, the degree and extend of which is important for the design, excavation and support of underground openings. The relevance of the EDZ for the geological isolation of nuclear waste disposal may be summarized as: 1) Relevance to near-field performance assessment. The EDZ is of importance for near-field performance assessment, as the development of new fractures and the opening of existing fractures due to excavation may create preferential pathways for mass transport from the engineered barrier system to natural transmissive flowpaths. 2) Relevance to the design, excavation and sealing of a repository. The excavation method affects the properties and the extend of the excavation damaged zone. The shape and the scale of the underground opening, and whether the underground opening is backfilled after excavation, will affect the final stress state. It is important to understand the EDZ for the design, excavation and sealing of a repository. 3) Initial and boundary conditions of in situ experiments. Information about the EDZ is necessary for the design and interpretation of certain in situ experiments. (author)

[en] A shaft, with a diameter of 6 m and a depth of 150 m, has been newly excavated in sedimentary rock and excavation response of rock mass around the shaft has been measured and analyzed. Excavation response has been evaluated based on the results of measurement of rock mass movement, such as displacement and strain, and change of rock property, such as deformability and permeability. This study indicates that rock property has been changed with in about 1 m from the shaft wall, and rock mass movement and property change has been influenced by rock facies, fracture and re-distributed stress. The relation between property change and these factors is remained to be evaluated in future study. (author)

[en] Rock mass displacement measurements have been performed to understand rock mass behavior and its dependence on excavation method during drift excavation at the Tono mine. Rock mass displacements of 1.46 mm and 0.67 mm have been measured at one meter (0.33D: blasting, 0.42D: machine, D: width of drift) from the walls of drifts excavated by the drill and blasting method and machine, respectively. Numerical analysis of rock mass displacements with Finite Element Method has been performed assuming an excavation disturbed zone. Measured and analysed rock mass displacements are consistent with each other for the drift excavation by the drill and blasting method. The excavation disturbed zone was narrower for the drift excavated by machine than for the drift excavated by the drill and blasting method. (author)