Research of long-term mechanical displaced behavior of soft rock

not registered; Ogawa, Toyokazu; Inoue, Hiroyuki*; not registered

For the safety assessment of geological waste disposal system, it is imperative to understand the long-term mechanical deformation characteristics of the near field rock mass. In the assessment, it is important to take into account that the rock mass will be subjected to different environments that will change with the progress of time: during construction; during operation of waste package burial; and after confinement. Among possible factors that may affect the long-term mechanical deformation characteristics of rock mass, there are nainly two factors investigated in this report: the effects of alternating dry and wet conditions (during construction); and the thermal effect (during the emplacement of waste packages). Mudstone samples are first exposed to dry and wet cycles, and/or to elevated ternperature conditions. Constant strain rate uniaxial compression tests are subsequently carried out on the samples. Test results of the uniaxial compression tests show: (1)Strength of the mudstone decreases and the deformation characteristics change due to dry and wet cycles. (2)Strength decreases slightly, and the deformation characteristics change a little due to pre-heat treatment. Effect is however small. Also discussed in the report is necessity of a numerical prediction analysis with the use of the experimental results on the two factors studied.