Abstract
In recent years, underground rock mass has been used for the construction of structures such as the underground power plants, caverns to store liquid natural gas, or underground repositories for radioactive wastes. In order to ensure long-term stability of a rock mass, the study of time-dependent fracturing is essential. Subcritical crack growth is known as one of the main causes of time-dependent fracturing of rock. Therefore, it is essential to investigate subcritical crack growth in rock. It has been shown that subcritical crack growth is influenced by surrounding environment. It was found that crack velocity increased in rock in water. For the construction of structures in a rock mass, the calcium ion concentration in groundwater around the structure can be high because of the large amount of cementitious materials. However, effect of calcium ion on subcritical crack growth in rock has not been investigated enough. In this study, subcritical crack growth in sedimentary rock was studied by using the load-relaxation method of the double-torsion test. Especially, we have conducted measurements in water with different calcium ion concentrations. All measurements have been conducted under controlled temperature. It was found that the crack velocity in water with high calcium ion concentration was lower than that in water with low calcium ion concentration. Therefore, the concentration of calcium ion in water is considered to have a significant effect on subcritical crack growth in rock. It is concluded that the water environment with high calcium ion concentration is suitable for the long-term stability of rock mass.
In recent years, underground rock mass has been used for the construction of structures such as the underground power plants, caverns to store liquid natural gas, or underground repositories for radioactive wastes. In order to ensure long-term stability of a rock mass surrounding structures, the study of time-dependent fracturing is essential. Subcritical crack growth is known as one of the main causes of time-dependent fracturing of rock. Therefore, it is essential to investigate subcritical crack growth in rock to ensure the long-term stability of a rock mass. From previous studies, it has been shown that subcritical crack growth is influenced by environmental conditions. For example, it was found that subcritical crack growth was significantly influenced by water (Atkinson and Rawlings, 1981; Nara et al., 2009). For the construction of structures in a rock mass, the calcium ion concentration in groundwater around the structure should be high because of the large amount of cementitious materials. Effect of calcium ion on subcritical crack growth in rock has not been clarified yet. In this study, the measurement of subcritical crack growth in sedimentary rock was conducted by using the load-relaxation method of the double-torsion(DT) test to clarify the influence of calcium ion on subcritical crack growth of in rock.
