Fundamental study on long-term stability of rock from the macroscopic point of view

In 1994, this project was started, a pneumatic creep testing machine was modified. Inada granite was purchased, and the preliminary tests such as P-wave velocity measurement and Schmidt hammer testing were carried out. In 1995, a specimen of Tage tuff under water-saturated condition had been loaded in uniaxial condition in the pneumatic creep testing machine. The uniaxial compression and tension tests, and the short-term creep test of Inada granite were also carried out in the servo-controlled testing machines to obtain the complete stress-strain curves. In 1996, creep, compression and tension tests were carried out. Though creep stress of Tage tuff was set at as low as 30% of the uniaxial compressive strength, creep strain was continuously increasing after elapsed time exceeded 2 years. Creep tests of sandstone and Inada granite were also carried out. Uniaxial compression, uniaxial tension tests of sandstone were carried out in servo-controlled testing machines to obtain the complete stress-strain curves. Also, indirect tension test was carried out to compare with the results obtained in uniaxial condition. Two types of pressure maintenance equipment were developed and examined. The hydraulic type equipment modified for long-term creep testing to ensure durability and stability was, found to be precise and reliable. The pneumatic type equipment newly developed was comparatively less precise and reliable. A constitutive equation of variable compliance type was discussed based on the experimental results. Several ways how to obtain a set of four constants required to solve the equation were described. The constant strain-rate test, comparing with creep, constant stress-rate and relaxation tests, is recommended to be most appropriate for obtaining constants readily and easily. Based on seven Japanese rocks, the effects of confining pressure and moisture content on the value of each constant were discussed. (J.P.N.)