Study on Proper Constitutive Model for Evaluation of Long Term Mechanical Behavior of Buffer Material

Hirai, Takashi; Tanai, Kenji ; Kikuchi, Hirohito*; Shigeno, Yoshimasa*; Namikawa, Tsutomu*; Takaji, Kazuhiko*; Onuma, Satoshi*

The objective of this report is to make a proposal of the proper constitutive models and parameters for the evaluation of the long term mechanical behavior of the buffer material in the engineered barrier system. In the second progress report by JNC, it was reported that the well designed engineered barrier system is stable and safety on mechanical support of the overpack to ensure stability and stress which acts on the overpack by using analysis which based on the popular constitutive models for the general caly soils. However, the buffer material which has swelling characteristics is considered not to be ordinary clay soils. So it is necessary to select the reliable constitutive models again. Therefor the proper models were selected again systematically in the several models which have been used for the assessment of the behavior of clay soils and the simulation analysis on the laboratory tests were carried out by using these models. From the result of the simulation analysis it appeared that the selected two models were alike to assess the behavior of the buffer material and the parameters which need to simulate the consolidation tests are different from those for the triaxial compression tests. Finally the analysis was conducted to evaluate the effect of the swelling of the overpack by the collosion and the self weight which causes the sedimentation of the overpack. From the analytical result, it was clarified that two kinds of parameter sets are necessary to evaluate the deformation and the stress of the buffer material in the engineered barrier system.