Information of subcritical crack growth in rock is essential to ensure the long-term integrity of a rock mass surrounding various structures and various architectures made of rock materials. In this study, using Carrara marble as a rock sample, subcritical crack growth was investigated experimentally. Especially, the load relaxation method of the double-torsion test was used for all measurement under controlled temperature and relative humidity. It was shown that the crack velocity in air increased with increasing temperature. The crack velocity increased with increasing the stress intensity factor. However, we found a region where the increase of the crack velocity with stress intensity factor was not significant. It is also found that the crack velocity in this region increased with temperature. This is similar to Region II of subcritical crack growth observed in glass in air. The Region II in glass is controlled by the mass-transport to the crack tip. In the case of rock, the transport of water to crack tip is important. In general, Region II is not observed for subcritical crack growth in rock materials, because rocks contain water. Since the porosity of Carrara marble is very low, the contained amount of water is also very small. Therefore, it is considered that Region II is observed in Carrara marble. Since the crack velocity increased in the environment with higher temperature, it is concluded that the condition with low temperature in air is desirable for the long-term integrity of a carbonate rock mass. Additionally, it is concluded that mass-transport is an important process for subcritical crack growth in rock with low porosity.
Long-term stability is essential for a rock mass surrounding structures such as the repositories of the radioactive waste in underground, the underground power plants, or the caverns for storing liquefied petroleum or natural gas. It is also essential to ensure the stability of rock slopes in open-pit mines for the safety in mining. For these purposes, a better understanding of time-dependent fracturing in rock is necessary. The study of time-dependent fracture propagation is therefore required in both designing rock engineering projects and preventing disasters in a rock mass.