Achievement for Fundamental Study of Subcritical Crack Growth in Rock and Its Ability of Future Development

To ensure the long-term integrity of a rock mass, understanding the time-dependent fracturing is essential. For this reason, the study of subcritical crack growth in rock has been conducted by various researchers. It has been clarified that the influence of water is significant for the increase of the crack velocity in rock. Even though the surrounding environment is alkali, the crack velocity in rock decreased if the concentration of calcium ion in water is high. This phenomenon is basically microscopic. Even though subcritical crack growth happens in a rock mass, it is impossible to detect this phenomenon, because the aperture of the crack is on the order of micrometer. Since the study of subcritical crack growth is fundamental, it is often considered that its application to rock engineering project is difficult. However, industry-academia collaboration related to radioactive waste disposal has been started after obtaining the result with high reproducibility and clarifying the influence of surrounding environment on the change of the crack velocity in various rock materials. In addition, some international collaboration has been started to research the influence of subcritical crack growth on the weathering in rock and time-dependent deformation in a rock mass under excavation. It is suggested that the future development is possible even though we conduct some fundamental studies which may be useless apparently for rock engineering projects and natural phenomena.