Experimental Study on Stress Corrosion and Vacuum Effect of Rocks

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At the beginning of the twenty one century, the large rock cavern for radioactive waste diaposal will be constructed within a rock mass at a depth of more than 1000m, in Japan. The stability of such large rock cavern must be guarantee over very long timescale. The prediction of long-term strength of rocks is indispensable for insuring long-term stability of the rock cavern.The strength of rocks under compression is affected by the density, the shape and the direction of cracks, the strain and stress rate of loading, the stress state , the temperature and the existence of water in vapor phase or in liquid phase, and so on. Some researchers have inducated that the strength of rocks in dependent on the subcritical crack growth due to stress corrosion and is proportional to the water vapor pressure in atmosphere. However, few experiments to verify this fact have been performed.In this research, to examine the influence of the water as the stress corrosion agent on the strength of rocks, a … More series of uniaxial compression tests under the water vapor pressure ranging from 10^<-3> to 10^3 Pa is conducted on Kitagishima granite and Kumamoto andesite. Furthermore, the stress corrosion index is determined, then the estimation of long-teem strength of rock is discussed. The main results obtained are follows :1.The elastic modulus are not affected by the stress corrosion due to water vapor, analyzing the stress strain curve obtained.2.The uniaxial compressive strength of both rocks increases with decreasing water vapor pressure. It is clarified that this effect is dependent on the stress corrosion.3.The values of the stress corrosion index obtained from the results are 36 in Kumamoto andesite and 61 in Kitagishima granite, based on the relation between uniaxial compressive strength and water vapor pressure. The linear relation is applicable to the range of water vapor pressure 10^<-3> to 10^3 Pa.4.The estimation of long-term strength of rock is discussed. The discover of an agent activating the stress corrosion is indispensable to estimate the long-term stability of rock cavern. Less