堤防被災箇所における変状機構解明事例からの考察

抄録

During the torrential rain on July 2006, the water level exceeded the design water level at the Nadabun station along Hii River. The trench excavation investigation was conducted at Imazaike, which is one of two places where the cave-in on the downstream surface and the leakage in the channel at the toe of dike were identified. The things carried out were the geotechnical investigations, the in-situ tests at the excavation site, and the water quality analyses. It is shown that the cave-in on the downstream surface should be due to a cavity caused by the piping and outflow of sand in the foundation ground below the dike body. It is considered that the main reason for the cave-in is the rising phreatic surface by spring water and seepage block caused by the existing dike-toe channel.