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

第三系沉积岩是一种软岩，被认为是隔离危险核废料的潜在寄主岩。在施工处置场地前，应研究的最大问题是明确隧道围岩附近因应力变化和干燥而形成的开挖破坏区水力特征。本研究采用本项目新研制的蒸发测井设备，对开发区非饱和渗流进行了基本评价。通过室内试验，验证了该装置测量井壁蒸发量的准确性，并在实际钻孔中进行了应用。本课题主要研究工作如下：^*研制可测量井眼小流量的蒸发测井设备。^*从蒸发测井设备的测量结果发展出一种新的渗透率估算技术^*该设备和渗透率估算技术在特瑞山地下实验室两个站点隧道的应用。（瑞士）和六所核废物处理场（日本）。^*评估软岩干燥致裂过程的实验室试验。所得结果如下：(1)当通过钻孔的空气流量小于101/min时，利用新型蒸发测井设备可以很好地测量井壁的蒸发。(2)成功估算了井壁后方岩石的水力导率。Mt. Terri实验室的蛋白石粘土的水力导电性估计值为10^<-12>cm/s。(3)蒸发测井设备可以很好地应用于实际问题。(4)通过观察裂隙的发生情况，测量了部分软岩试样在干燥过程中的体积变化。

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.