Unsaturated groundwater flow and pollutant migration in EDZ of tunnels excavated in soft rock for nuclear waste disposal

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Tertiary sedimentary rock that is classified as a kind of soft rock has been thought as a potential host rock for isolating hazardous nuclear waste. The biggest problem should be studied before constructing disposal site is to make clear the hydraulic feature of excavation damaged zone(EDZ) that is formed near tunnel wall due to the stress change and drying. In this research, the unsaturated flow in the EDZ was basically evaluated by using the evaporation logging equipment that was newly developed in this project. The accuracy of the evaporation measurement from the bore-hole wall was validated by the laboratory tests, then, this equipment was applied in some actual bore-holes.The major items of this research works in this project are as follows :^*Development of evaporation logging equipment that can measure the little in-flow into a bore holes.^*Development of a new permeability estimation technique from the measured result by the evaporation logging equipment^*Application of the equipment and the permeability estimation technique to tunnels in two sites, the Mt.Terri Under ground Research Lab. (Switzerland) and the Rokkasho Nuclear Waste Disposal Site (Japan).^*Laboratory test for evaluating the fracturing process due to the drying of soft rock.Results obtained are as follows ;(1)Evaporation from bore-hole wall could be well measured by using the new evaporation logging equipment when the air discharge passing through the bore-hole was less than 101/min.(2)Estimation of the hydraulic conductivity of the rock just behind the bore-hole wall was successfully performed. The hydraulic conductivity values estimated for the Opalinus Clay of the Mt. Terri Laboratory were in the order of 10^<-12>cm/s.(3)It was clearly found that the evaporation logging equipment could be well applied to the actual problems.(4)The volumetric change of some kinds of soft rock specimen due to the drying was measured with observing the occurrence of fractures.