Twenty-Year Creep Test with Tuff under Uniaxial Compression

<jats:title>Abstract</jats:title> <jats:p>A creep test is a helpful method for investigating the long-term deformation of rock. However, most previous creep tests on rock were carried out for less than a few weeks, and only a handful were performed for longer time periods. This article reports an ongoing long-term creep test that was started in 1997 and reached its twentieth year in 2017. This uniaxial compressive creep test has been conducted with tuff under water at a creep stress of 30 % of its short-term strength. An overview of the creep test is described first in this article, including the test method and long-term maintenance. Daily maintenance and countermeasures against possible problems are indispensable so as to not require halting of the test. During the test, the test apparatus was transferred twice due to the reconstruction of the building containing the laboratory, but the test was not halted during the transfers. The recorded creep strain over a period of 20 years included a variety of environmental noise such as slight changes in the air pressure in the cylinder and in temperature and humidity. Hence, annual averages of the strain were used for understanding the long-term trend, and the trend was found to be approximated by a power function of time. The recorded creep strain was compared with the results of short-term creep tests and the stress-strain curves in strength tests. The authors believe that the test in this study is the longest uniaxial compressive creep test with a rock specimen that has been carried out.</jats:p>