Learning from Earthquakes: First person reports


Shideh Dashti’s Geotechnical Observations from Trip to Sendai, Japan

June 7, 2011 by
Filed under EERI Team Field Blog, Geotechnical, Structural, Tsunami

June 3, 2011:

After meeting our Japanese colleagues on Friday, June 3rd at the hotel, we took the train from Narita Hilton Hotel to Tokyo and then Sendai. In Sendai, we first visited the Tohoku Regional Development Bureau (MLIT). They described the existing emergency response protocols for earthquake and tsunami. We then headed to the Sendai-Tohbu Viaduct (East Nippon Expressway Co. Ltd), a bridge with failed elastomeric bearings during the March 11th earthquake. There was very little evidence of liquefaction near the bridge, but the softening of the foundation soil in general seemed to be a minor and local effect that did not influence the performance of the bridge.

June 4, 2011:

We headed for the coastal areas that were damaged the most due to the tsunami (about 2-hour ride with the bus from Sendai). The scale of the damage was significant, miles and miles of complete destruction. We saw groups of volunteers from around the country working to help clean up the debris.

We first visited the Mizushiri hashi bridge. The piers seemed to have performed well, but the deck washed away. A smaller adjacent bridge had evidence of scouring and rotated columns. Although it was difficult to verify closely, their foundation seemed to be in place with no damage. But the columns and their connecting steel reinforcement to the lower pile cap seemed to have failed due to flow.

Later in the day, we visited a bridge that was slightly affected by soil liquefaction near the abutments. More importantly, we observed the failure of a section of a levee adjacent to the bridge. This failure was due to liquefaction and countermeasures were already in place before the rainy season in Japan begins (around June). They had completed a temporary river dike with sheet pile walls, which will be removed after the dike is permanently repaired.

June 5, 2011:

We visited a few bridges that had been retrofitted following the 1978 earthquake in Japan. Some performed well under the experienced ground motions, some didn’t. There was one bridge that suffered damage only during a strong aftershock.

There was considerable evidence of liquefaction near these bridges. Sink holes were observed near the piers. In some cases, the entire area was covered with sand ejecta. However, the bridge columns were founded on piles and did not seem to have been affected by soil softening and the settlement of the surrounding soil.

June 6, 2011:

We took the train back to Tokyo from Sendai in the morning. After visiting one bridge, we visited a site located south-east of Tokyo with buildings that were affected by liquefaction (Urayasu-Shi). Soil softening had caused significant damage to pipelines and manholes as well as sidewalks.  In many cases, the ground had settled in a non-uniform manner around the buildings (up to 14-15 inches), but structures that were on pile foundations had not moved and were intact. One structure that appeared to have shallow foundations had settled more than the surrounding soil, as expected. There was evidence of lateral spreading near a bridge as well, causing very minor damage (movement in the order of 1 to 2 inches).  Liquefaction is “Ekijyoka” in Japanese.

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