The effects of a shaft excavation experiment on the hydrology of the Tono research field, Japan

In order to understand the groundwater flow deep underground and its long term evolution in the future, it is necessary to develop a comprehensive hydrological evaluation system including in-situ investigation methodology, instrumentation for measurement and an assessment method such as numerical simulation. A hydrological evaluation system was developed and a project was planned to confirm the efficiency of the system. The project, named the Shaft Excavation Effect Project, in which a shaft 6 m in diameter and 150 m in depth was excavated and the system was applied to evaluate the shaft excavation effect on groundwater flow. The following results were obtained. 1. The recharge rate from the unconsolidated formation into the rock mass underneath was calculated to be 0.57 mm day^-1. 2. The hydrogeological model was classified into 12 groups according to the results from a geological survey, geophysical logging and in-situ hydraulic tests. 3. The predictive simulation and the subsequent observation showed good agreement, namely: the area where pore water pressure was considerably influenced by the excavation was within a range of 100m around the shaft; the inflow into the pre-existing shaft and the drift was not affected by the excavation of the new shaft. 4. The efficiency of the hydrological evaluation system has been confirmed.