Study of hydrogeology in the Mizunami Underground Research Laboratory project. Hydrogeological modeling and groundwater flow simulation based on data of hydraulic and geochemical impacts during the construction of the MIU facilities. FY 2009

One of the goals of the Mizunami Underground Research Laboratory (MIU) Project is to develop technical basis for investigation, analysis and evaluation technologies for understanding the deep underground geological environment in various scales. Understanding groundwater flow system is one of the important issues in the project, and to achieve this purpose, technologies for hydrogeological model and groundwater flow simulation technique, have to be established. In this study, hydrogeological modeling and groundwater flow simulations focused on the Site Scale Area have been carried out in order to revise the hydrogeological model and to predict changes of hydraulic and geochemical conditions around the MIU Construction Site and inflow rate into the MIU facilities using the result of Surface-based Investigation phase (Phase I), the data of hydraulic responses in monitoring boreholes, inflow rate into the MIU facilities and the result of geological mapping until 300m depth in Construction phase (Phase II). As a result of this study, the significant hydrogeological structures around the MIU Construction Site were estimated. The inflow rate into the MIU facilities and hydraulic and geochemical impacts around the MIU Construction Site caused by the MIU facilities construction were predicted. The effect of pre-grouting to the MIU facilities was also confirmed. (author)