PRELIMINARY OBSERVATIONS OF LEVEE PERFORMANCE FOLLOWING THE MARCH 11, 2011 TOHOKU OFFSHORE EARTHQUAKE, JAPAN

摘要

The March 11, 2011 Tohoku Offshore Earthquake was one of the largest earthquakes recorded in the last century. The large and prolonged shaking from this Magnitude 9 earthquake, together with the resulting tsunami, caused widespread destruction and countless personal tragedies. The earthquake produced moderate to large shaking along the east coast of the island of Honshu for several hundred kilometers with durations of shaking often as high as two minutes. It also provided a rare opportunity to document the performance of a large number of levees for both long duration shaking and for tsunami overtopping. The authors were fortunate to be part of a team organized by the Geotechnical Extreme Events Reconnaissance Association and sent to Japan to work with our Japanese colleagues to collect information on the performance of levees. As part of this reconnaissance, levees were inspected in both the Tohoku and Kanto regions, with particular focus on the eastern parts of the Miyagi and Ibaraki prefectures. Much of the extant information available on levee performance had already been documented by the Ministry of Land, Infrastructure, and Transportation and by the Tokyo Institute of Technology. These agencies and their principal investigators graciously shared this information with the authors and helped identify levee reaches with different types of performance. While most levees performed well, there were hundreds, if not thousands, of limited reaches where minor to major structural damage was caused by foundation liquefaction. Since the river levels were low at the time of the earthquake, no levees actually breached and caused inundation of the protected areas due to earthquake shaking. However, in the coastal areas, tsunami waves overtopped both the coastal and riverine levees and floodwalls, and caused tremendous damage and loss of life. This paper presents some of the observations made during our reconnaissance and the information provided by our Japanese colleagues. In addition to performance information, this paper also describes some of the interim and permanent levee repair techniques used by the Japanese to repair earthquake and tsunami damage.