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[J09-2-04] Vertical Deformation Following Groundwater Drawdown by Excavating of 500 m Depth Shafts in Granite in Mizunami, central Japan in 2004-2016
Two investigation shafts of 500 m depth were excavating in the granite body in Mizunami, central Japan by JAEA (Japan Nuclear Cycle Development Institute) in 2004-2012. Groundwater of 800 ton is generally pumping a day to prevent the shafts from submerging now. As a result of pumping the groundwater, the ground water level lowered to 80 m in the borehole with the distance of 200 m from the excavating shafts in 2016.Leveling network extending 2 km x 2 km around the shafts was established to detect the vertical deformation around the shafts in 2004, and precise leveling was done every year. An 18 mm ground subsidence was detected in the benchmark close to the shafts for 8 years in 2004-2012, and time series of subsidence at benchmark was consistent with the groundwater drawdown. The groundwater drawdown and ground subsidence were caused by the pumping ground water in excavating shafts.
In 2012, we extended the leveling network to a width of 4 x 5 km around the excavating shafts, and we had precise leveling at the network every year since 2012 to 2016. As results, subsidence of 8 mm is detected in the area in the southeastern are from the shafts side.
A depth distribution of granite in the area is estimated from aeromagnetic surveying. As results, two groundwater veins are suggested in NW to SE and NNE to SSW. Beneath the shafts, groundwater is flowing to southeast from northwest. A subsidence of 8 mm is detected along the groundwater, not only vicinity of the shafts. It is a good fruitful result to make clear the ground deformation by precise leveling.
In 2012, we extended the leveling network to a width of 4 x 5 km around the excavating shafts, and we had precise leveling at the network every year since 2012 to 2016. As results, subsidence of 8 mm is detected in the area in the southeastern are from the shafts side.
A depth distribution of granite in the area is estimated from aeromagnetic surveying. As results, two groundwater veins are suggested in NW to SE and NNE to SSW. Beneath the shafts, groundwater is flowing to southeast from northwest. A subsidence of 8 mm is detected along the groundwater, not only vicinity of the shafts. It is a good fruitful result to make clear the ground deformation by precise leveling.