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Japan Earthquake/Tsunami Reconnaissance Team 2 -- Days 3 and 4

Devastating Failures in Fukushima Prefecture

A team from the Embankment, Dams and Slopes (EDS) Committee of the Geo-Institute arrived in Japan on April 23 for a one-week engineering reconnaissance of the region affected by the Tohoku Japan earthquake. The three-person team is led by Joseph Wartman, Ph.D., P.E., M.ASCE, of the University of Washington, and includes Binod Tiwari, M.ASCE, of California State University, Fullerton, and Daniel E. Pradel, Ph.D., P.E., D.GE, F.ASCE, of Praad Geotechnical Inc. and the University of California, Los Angeles. The EDS/GI team is being hosted by Professor Keizo Ugai, president of the Japanese Landslide Society and an instructor at Gunma University. The team is also working with the Japanese Geotechnical Society. Team members will be posting updates to the ASCE web site throughout the week. 

Read each day's entries:
Days 1 and 2  |  Days 3 and 4  |  Days 5 and 6 

Days 3 and 4 -- Tuesday, April 26 and Wednesday, April 27

Report by Joseph Wartman 

The GI/EDS team has been traveling throughout the general Fukushima region over the past two days. Owing to its very large magnitude, the mesoseismal area of the earthquake (i.e., region experiencing strong ground shaking) is enormous and this presents both a challenge and opportunity for our engineering reconnaissance. The challenge is trying to optimize the reconnaissance so that we may cover as much ground as needed in a limited amount of time -- and before cleanup and repair efforts obscure the damage mechanisms. Our Japanese colleagues have been extraordinarily helpful in this regard as they have already visited many of the sites of interest and have been able to show us those that are the most significant. The unique opportunity that the large magnitude earthquake provides is the chance to witness the effects of strong ground shaking on a wide range of geotechnical systems situated in a variety of geological settings.

Today we visited the site of the Fukushima Dam, which catastrophically failed during the earthquake, tragically killing 12 residents of a nearby town, as seen below. The 17-meter dam impounded water used for agricultural purposes. In addition to the dam failure, during our visit we witnessed instability in some of the slopes surrounding the reservoir. It is not clear why the dam failed, but this will undoubtedly be the topic of future forensic investigations.

Fukushima dam failure 
While road infrastructure typically performed very well in this region, we visited one large failure yesterday where a portion of road embankment that slid several tens-of-meters downslope. The failure appears to have involved a wedge of fill that was placed to grade the road.

Road embankment failure

We have also visited several landslides in natural or modified terrain, including one long-runout event shown in the photo below that impacted three houses. This landslide was not triggered by the main shock, but instead by the April 11 shallow event described in our previous post. The landslide killed several people in the homes.

Landslide around homes

Days 1 and 2  |  Days 3 and 4  |  Days 5 and 6
 

 

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