Abstract
Hachiro-Gata Impoldering Project is one of the greatest impoldering works which have been performed in Japan. The major part of the lagoon bottom is covered with deep and very soft clay deposits and some parts of the polder dikes are compelled to be built on these bad subsoils. Two types of test dikes, that is replacement type and sand-bed type, were built to examine the calculated results of dike design before the construction of dikes.The authors intend to present the characteristics of Hachiro-Gata Clay and some investigations observed during the construction of test dikes, including dike failure test performed on them.
