Theoretical study on crystalline rock for estimating long-term behavior (Contract research)

The Japan Atomic Energy Agency (JAEA) is conducting the Mizunami Underground Research Laboratory (MIU) Project in order to develop comprehensive geological investigation and engineering techniques for deep underground applications (e.g. repository of HLW). The purpose of this study is to contribute to the evaluation of the mechanical stability of a research drift and to plan the future studies. Rock shows time-dependent behavior such as creep/relaxation. For the shaft and gallery of the geological disposal for the radioactive waste, the mechanical stability over a period of thousands of years is demanded not only during construction and operation but also after back-filling. So, to understand the time-dependent behavior of rock is very important for evaluating the long-term mechanical stability. In this research, we aim to clarify a long-term behavior of crystalline rocks, and performed the following subjects: 1) Theory establishment to pressure dissolution of quartz and a homogenization analysis for quartz dissolution. 2) Uniaxial and stress relaxation tests under observation of a con-focal laser scanning microscope (CLSM) by using granite specimens of MIU. 3) Strong discontinuity analysis introduced in a micro-scale problem of the multi-scale homogenization analysis for applying Toki granite samples. This report describes the results of the works in the fiscal year 2007. In Chapter 1, we described the overview and background of this study. In Chapter 2 a reaction theory of pressure dissolution of quartz was proposed and by using a homogenization analysis the dissolution of quartz in bentonite was simulated by a modified diffusion model. In Chapter 3 CLSM was used to acquire clearly focused three-dimensional images of granite specimens of MIU for stress relaxation tests, and observed the change of micro-scale structure including the mineral configuration under applying compression stress. The local strain distributions suggest that a shearing mode is dominant in the granite samples. In Chapter 4 a strong discontinuity concept is introduced in the micro-scale problem of the multi-scale homogenization analysis, and Toki granite sample problems were solved. (authors)