Fujinuma Dam Performance during 2011 Tohoku Earthquake Japan and Failure Mechanism by FEM

Fujinuma Dam Failure and Human Casualty Analysis of failure mechanism and resident sedulity policy 86Reservoir and agriculture dams were damage during the 3.11 East Japan earthquake. Among them, Fujinuma Dam located in Fukushima prefecture had severe damage of earth dam -embankment, causing 8 person casualties. The dam is an earth-dam constructed 62 years ago. The bank of 18 m height and 133m length failed just after earthquake occurrence. Human casualty by dam failure is the first event since 1930. Only 140,000,000 Yen will be supported by Central Government for this dam failure restoration no Tsunami occurred in this area and failure was considered to be caused by ground shaking. Based on our field survey and hearing investigation to residents, at first, Black water flow in the river and many persons escaped from river side to mountain areas. A lot of water attacked residential area, especially at the curved corner of river route. The maximum acceleration at this area was about 403 gal by K-Net recording. The dam was not designed under consideration of seismic forces though the current design considered 700 gal acceleration spectra for earth-dam. To make clear the mechanism of dam failure, FEM analysis had been done and compared to the resisting capacity of the dam embankment. The results show that the dam failure is considered to occur just after the earthquake, not by the penetration of ground water long after the earthquake. The Liquefaction phenomena may be concerned to the failure mechanism. After that， resident security policy in that area has been investigated. Human casualty is the serious problem due to dam failure.