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Takayama, Yusuke
International Journal of Rock Mechanics and Mining Sciences, 136, p.104538_1 - 104538_8, 2020/12
Times Cited Count：3 Percentile：24.61(Engineering, Geological)It is necessary to apply reliable numerical simulation techniques to assess the mechanical behaviour of repositories for the geological disposal of radioactive waste over a long period of time. Having a constitutive model that can describe the mechanical behaviour of bentonite is key to such numerical simulations. In this study, the applicability of linear elastic constitutive model with swelling term is examined focusing on the density heterogeneity by applying to the in situ Full-scale Engineered Barrier Experiment (FEBEX) in Grimsel. It was confirmed that this constitutive model underestimates the density change. Instead, mechanical behaviour was re-simulated by unsaturated elasto-plastic constitutive model using the changes in degree of saturation as input data. Although no feedback effects of mechanical behaviour on hydraulic and thermal behaviour were taken into account, two-dimensional stress and density could be reproduced.
Takayama, Yusuke; Kikuchi, Hirohito*
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 27(1), p.12 - 21, 2020/06
In this study, an applicability of the modified Cam clay model to the buffer material under saltwater conditions was examined. First, consolidated-undrained triaxial test was conducted using NaCl solution and artificial seawater. Based on the consolidated-undrained triaxial compression test results and the existing consolidation test results, the difference in the mechanical behavior of the buffer material under distilled water and saltwater condition was clarified. In particular, there was a difference in the unloading behavior in the consolidation test. Through reproducibility analysis of these experimental data, it was confirmed that the mechanical behavior of the buffer material can be roughly reproduced by setting the swelling index according to the salt concentration.
Takayama, Yusuke
no journal, ,
It is important to know the state of the barrier at the end of the transient period, in particular the degree of density homogeneity achieved at that stage. In this study, the validity of the existing coupling model is examined focusing, among other things, on the density heterogeneity by applying to the in situ Full-scale Engineered Barrier Experiment (FEBEX) in Grimsel. It was confirmed that linear elastic constitutive model with swelling term applied to the existing coupling model underestimates the density change. Instead, mechanical behavior was re-simulated by unsaturated elasto-plastic constitutive model using the changes in degree of saturation as input data. Although no feedback effects of mechanical behavior on hydraulic and thermal behavior were taken into account, two-dimensional stress and density could be reproduced. Further studies might be required, (1) three dimensional effects on deformation and (2) coupling effects between thermal, hydraulic and mechanical behavior in density heterogeneity. The long-term measurement data and sampling data of three-dimensional spatial distribution of FEBEX and other in-situ tests could also contribute to these further model studies.
