Phenomelogical study on crystalline rock for evaluating of 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 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 stability of rock structures. This study is aiming to find out the mechanism of time-dependent behavior of rock such as creep by the precision test, observation and measurement, to develop the evaluating method of long-term behavior of rock mass, and to get the information for planning the study of the Phase III (Operation Phase) at the Mizunami URL. This report describes the results of the works in the fiscal years of 2005 and 2006. In Chapter 2, as the fundamental study on time-dependent behavior, followings were described; 1) The result of continuing creep test of Tage tuff which was started from the fiscal year of 1997. 2) The results of multi-stage creep test of Inada granite at mid-range temperature. 3) The consideration of the generalized relaxation test which is integrated and extended creep test and relaxation test. 4) The consideration of new testing method to determine the parameter in the constitutive equation supposed by Okubo. In Chapter 3, followings were described; 1) The results of rock mechanical tests of Toki granite. 2) The results of obtained parameters for the constitutive equation considering time-dependent behavior by mechanical tests and numerical simulations. Furthermore, in this report, following two related studies were attached in appendix; 1) Study on evaluating the effects of scatter in in-situ rock properties. 2) Study on new rock classification method considering long-term behavior of rock mass. (author)