Development of an Analysis Methods for the Progressive Failure of Discontinuous Solids

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Deformation in excavation disturbed zone is investigated by a model tunnel of high level nuclear waste repository. The experiment is conducted using artificial soft rock under a plane strain condition. The deformation is measured by a newly developed measurement system which consists of a microscope and a high precision X-Y stage. From the experiment, it is clarified that a wedge shaped damaged zone is formed during the course of stress redistribution. Taking into account the result of the experiment new tunnel design concept is proposed, in which the formation of the wedge shaped damaged zone is considered to be the final stage of tunnel breakage. A numerical analysis method is developed by introducing an interface element which enables us to analyze propagation of rupture zone and the formation of the wedge shaped damaged zone. From the analysis, it is shown that the design depth is deepened by adopting a formation of rapture zone in the excavation disturbed zone. In the present study, creep experiment is also conducted using artificial soft rock, in order to clarify the mechanism of creep rapture. In the experiment, displacement field is measured by the measurement system developed in the present study. From the experiment, the deformation field is heterogeneous from the very first stage of stress state, in the case of high state, in the case of high stress level which is comparable with the capacity of the material. On the contrary, in the cased of low stress level, the deformation field is almost homogeneous and the shear band which is observed almost from the beginning of a test in the case of high stress level is not formed until the creep rapture takes place. From the experiment, it is clarified that the development of a model based on the mechanism of creep rapture and localization mode is indispensable in order to evaluate long term safety of underground structures, in which the creep rupture becomes a dominant problem to be clarified.