PSI - Issue 13

Yoshitaka Nara et al. / Procedia Structural Integrity 13 (2018) 222–225 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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5. Discussion

To ensure the long-term stability of a rock mass surrounding various structures, it is essential to know what influences the long-term strength of rocks. It has been clarified that the long-term strength of rock is influenced by the environmental conditions, such as humidity (Nara et al., 2013) and existence of water (Nara et al., 2017), and the preferred orientation of cracks (Nara, 2015). Since the long-term strength can be evaluated by considering the crack propagation, it is essential to know the condition where the crack velocity decreases. Since the crack velocity in rock in water is higher than that in air, the dry condition is desirable for the log-term stability. In addition, it will be effective to seal the network of cracks and pores to prevent the water flow in rock (Wang et al., 2016; Pérez-Flores et al., 2017, Nara et al., 2018b). In this study, we found that the water with high calcium ion concentration is desirable for the prevention of crack growth even though pH is high. This is the new finding of this study, because it has been considered that a basic solution such as NaOH facilitates the crack growth in silicate rock (Sano and Kudo, 1992). The result of this study can contribute the long-term stability of the rock mass. In this study, the influence of surrounding environment on SCG in Berea sandstone in water was investigated. Especially, we have conducted the measurements of SCG in Berea sandstone in distilled water and Ca(OH) 2 with the concentration of 600 mg/L. It was shown that the crack velocity at a constant stress intensity factor in Ca(OH)2 was lower than that in distilled water, even though Ca(OH) 2 is a basic solution. Since the crack velocity in silicate rock increased in a basic solution, this result is a new finding of this study. It is considered that high calcium ion concentration affected the decrease of the crack velocity. It is concluded that the aqueous condition with high calcium ion concentration is suitable to ensure the long-term stability of a sedimentary rock mass surrounding various structures. Anderson, O.L., Grew, P.C., 1977. Stress corrosion theory of crack propagation with applications to geophysics. Review of Geophysics and Space Physics 15, 77-104. Atkinson, B.K., 1984. Subcritical crack growth in geological materials. Journal of Geophysical Research 89, 4077-4114. Evans, A.G., 1972. A method for evaluating the time-dependent failure characteristics of brittle materials – and its application to polycrystalline alumina. Journal of Materials Science 7, 1137-1146. Nara, Y., 2015. Effect of anisotropy on the long-term strength of granite. Rock Mechanics and Rock Engineering 48, 959-969. Nara, Y., Takada, M., Igarashi, T., Hiroyoshi, N., Kaneko, K., 2009. Subcritical crack growth in rocks in an aqueous environment. Exploration Geophysics 40, 163-171. Nara, Y., Hiroyoshi, N., Yoneda, T., Kaneko, K., 2010. Effect of temperature and relative humidity on subcritical crack growth in igneous rock. International Journal of Rock Mechanics and Mining Sciences 47, 640-646. Nara, Y., Morimoto, K., Yoneda, T., Hiroyoshi, N., Kaneko, K., 2011. Effects of humidity and temperature on subcritical crack growth in sandstone. International Journal of Solids and Structures 48, 1130-1140. Nara, Y., Morimoto, K., Hiroyoshi, N., Yoneda, T., Kaneko, K., Benson, P.M., 2012. Influence of relative humidity on fracture toughness of rock: implications for subcritical crack growth. International Journal of Solids and Structures 49, 2471-2481. Nara, Y., Yamanaka, H., Oe, Y., Kaneko, K., 2013. Influence of temperature and water on subcritical crack growth parameters and long-term strength for igneous rocks. Geophysical Journal International 193, 47-60. Nara, Y., Nakabayashi, R., Maruyama, M., Hiroyoshi, N., Yoneda, T., Kaneko, K., 2014. Influences of electrolyte concentration on subcritical crack growth in sandstone in water. Engineering Geology 179, 41-49. Nara, Y., Tanaka,M., Harui, T., 2017. Evaluating long-termstrength of rock under changing environments fromair towater. Engineering FractureMechanics 178, 201-211. Nara, Y., Harui, T., Kashiwaya, K., 2018a. Influence of calcium ions on subcritical crack growth in granite. International Journal of Rock Mechanics and Mining Sciences 102, 71-77. Nara, Y., Kato, M., Niri, R., Kohno, M., Sato, T., Fukuda, D., Sato, T., Takahashi, M., 2018b. Permeability of granite including macro-fracture naturally filled with fine-grained minerals. Pure and Applied Geophysics 175, 917-927. Pérez-Flores, P., Wang, G., Mitchell, T.M., Meredith, P.G., Nara, Y., Sakar, V., Cembrano, J., 2017. The effect of offset on fracture permeability of rocks from the Andean Southern Volcanic Zone, Chile. Journal of Structural Geology 104, 142-158. Sano, O., Kudo, Y., 1992. Relation of fracture resistance to fabric for granitic rocks. Pure and Applied Geophysics 138, 657-677. Wang, G., Mitchell, T.M., Meredith, P.G., Nara, Y., Wu, Z., 2016. Influence of gouge thickness on permeability of macro-fractured basalt. Journal of Geophysical Research - Solid Earth 121, 8472-8487. Williams, D.P., Evans, A.G., 1973. A simple method for studying slow crack growth. Journal of Testing and Evaluation 1, 264-270. 6. Conclusion References