Abstract
The distribution of the change in groundwater volume at the site of Mizunami Underground Research Laboratory in the Tono area, Japan, was estimated by the inverse method proposed by the authors, using tilt data measured with four tiltmeters at the surface during drainage, submergence and re-drainage in excavation of shafts. Furthermore, the reliability of the results was evaluated by a model analysis for groundwater flow in a single ellipsoidal field. The results showed that the hydrogeological structure for the region of 1000m×1000m in area and 100m to 180m in depth is such that groundwater flow occurs mainly in a region between two impermeable faults with the center at 100m to 150m south of the Main shaft and this region tends to shrink toward north-west and be widened toward south to south-east. However, at the same time, the model analysis showed that areas north-west and south-east of the Main shaft in the corners of the region are vacua for estimation due to the aligned layout of the tiltmeters.
