Phenomenological study on crystalline rock for evaluating of long-term behavior (Contract research)

Rock shows time-dependent behavior such as creep/relaxation. On the radioactive waste disposal, the long-term mechanical stability of shaft and gallery excavated in rock were required, over a period of thousands of years not only during construction and operation but also after back-filling. Therefore, it is very important to understand the time-dependent behavior of rock for evaluating the long-term mechanical stability. The purpose of this study is finding out the mechanism of time-dependent behavior of rock by the precision test, observation and measurement, to develop the method evaluating of long-term mechanical stability. In the previous work, the testing technique has been established and the basic of evaluating method was developed. Recently, some parameters needed for simulation of time-dependent behavior at Mizunami underground facilities were determined. But we have not enough to check on reliability of the evaluating method, of these parameters. This report describes the results of the works in the fiscal year 2008. In Chapter 1, we described the overview and background of this study. In Chapter 2, the creep testing system including a testing machine, pressure control equipments, sensors and meters were reviewed on the basis of more than 10 years experience. The long-term creep test of Tage tuff was continuously conducted and the total testing time exceeded 11 years. The strain was increasing at very low speed and the strain rate was decreasing following elapsed time to powers of -0.9. This behavior is likely to previous result of short-term test. In Chapter 3, in order to test along any relaxation pattern, the control program to conduct generalized relaxation testing in a servo-controlled testing machine was extended. Then, generalized relaxation test of Toki granite were carried out successfully. The parameters in the variable-compliance-type constitutive equation for Toki granite were deduced. In Chapter 4, fundamental concept of the constitutive equation was described and parameter-obtaining methods for this constitutive equation were reviewed and criticized. In the final part, an idea of new rock characterization where time-dependent behavior of rock is considered as the very important factor was proposed. (author)