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Takachi, Kazuhiko; Taniguchi, Wataru
JNC TN8400 99-042, 68 Pages, 1999/11
The buffer material is expected to maintain its low water permeability, self-sealing properties, radionuclides adsorption and retardation properties, thermal conductivity, chemical buffering properties, overpack supporting properties, stress buffering properties, etc. over a long period of time. Natural clay is mentioned as a material that can relatively satisfy above. Among the kinds of natural clay, bentonite when compacted is superior because (1)it has exceptionally low water permeability and properties to control the movement of water in buffer, (2)it fills void spaces in the buffer and fractures in the host rock as it swells upon water uptake, (3)it has the ability to exchange cations and to adsorb cationic radioelements. In order to confirm these functions for the purpose of safety assessment, it is necessary to evaluate buffer properties through laboratory tests and engineering-scale tests, and to make assessments based on the ranges in the data obtained. This report describes the procedures, test conditions, results and examinations on the buffer material of dynamic triaxial tests, measurement of elastic wave velocity and liquefaction tests that aim at getting hold of dynamic mechanical properties. MWe can get hold of dependency on the shearing strain of the shearing modulus and hysteresis damping constant, the application for the mechanical model etc. by dynamic triaxial tests, the acceptability of maximum shearing modulus obtained from dynamic triaxial tests etc. by measurement of elastic wave velocity and dynamic strength caused by cyclic stress etc. by liquefaction tests.
; ; Sakaki, Toshihiro;
PNC TN7410 94-049, 105 Pages, 1994/09
Excavation of a shaft or a horizontal drift in a rock mass probably affects the rock mass around the openings. It is necessary in the design, construction and safety assessment of underground facilities to consider the properties and extent of the EDZ (Excavation Disturbed Zone; the zone where rock properties and rock conditions have been changed due to excavation). PNC has carried out the in-situ experiments in the Tono mine and has identified the controlling factors in the generation and extent of the EDZ due to blasting. In order to evaluate dependence of the generation and extent of the EDZ on excavation method, Machine Bxcavation Effects Experiment has been started. In FY 1992, a horizontal drift for measurements (measuring drift) was excavated. A horizontal drift parallel to the measuring drift (test drift) is scheduled to be excavated by a machine in FY 1994. The investigations and numerical analysis before excavation of the test drift were carried out in FY 1993. The objectives of the investigations and numerical analysis carried out in FY 1993 are as follows: (1)to measure and evaluate the rock properties and the rock conditions around the test drift before excavation, and (2)to predict by numerical analysis the displacements and stress change during excavation of the test drift. The investigations and numerical analysis in FY 1993 consist of the following items: (1)laboratory tests to measure the compressive strength, deformation modulus, seismic wave velocity, electric resistivity, and so on, (2)in-situ tests to estimate deformability and permeability, (3)borehole wall observation, (4)measurement of the initial stress, (5)seismic tomography and resistivity tomography, and (6)numerical analysis to predict the displacements and stress change by the Finite Blement Method. This report describes the details of these investigations and numerical analysis carried out in FY 1993.
