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Takayama, Yusuke; Tachibana, Shinya*; Iizuka, Atsushi*; Kawai, Katsuyuki*; Kobayashi, Ichizo*
Soils and Foundations, 57(1), p.80 - 91, 2017/02
Times Cited Count：1 Percentile：77.48(Engineering, Geological)Bentonite has remarkable swelling characteristics and low permeability that makes it a suitable buffer material in a purpose built repository for the geological disposal of radioactive waste. It is necessary to use reliable numerical simulation techniques to demonstrate that the repository is safe and mechanically stable for tens of thousands of years. Constitutive model that describes the mechanical behavior of bentonite is a key technique in such numerical simulations. The current paper proposes a constitutive model for bentonite, which treats bentonite as an unsaturated elasto-plastic material that changes its mechanical properties as it becomes saturated. In the proposed model, the swelling index and an expression formula for negative dilatancy are treated as functions of degree-of-saturation. Montmorillonite content is used as an input parameter in the proposed model and so is applicable to a variety of bentonite based materials of varying montmorillonite content. Experimental results from swelling volume and swelling pressure tests taken from the literature are shown to be satisfactorily predicted by the proposed model.
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.
