Many flood protection dikes were damaged in both eastern and western Hokkaido, Japan during large earthquakes in 1993 and 1994 due to liquefaction in the foundations. A criterion based on crest settlement was developed for prioritizing remediation of the diking system to resist future earthquakes. The potential crest settlement during earthquakes of M=7.5 to M=8.0 was expressed in terms of geometrical properties of the dike cross-section. The procedure used to estimate the settlements was first used to simulate dike failures in eastern Hokkaido. Then, blind prediction tests were carried out for typical dikes in western Hokkaido. These predictions were then checked against actual field performance. The criterion proved to be very effective in predicting the performance of the damaged dikes.
Flood protection dikes along the Kushiro and Tokachi rivers suffered considerable damage during the 1993 Kushiro-oki earthquake off eastern Hokkaido, Japan. Damage included longitudinal and transverse cracks, slope failures and cave-ins. The more severely damaged dike sections were 6 m – 8 m high, and were constructed of compacted sand fill resting on a comparatively thick peat layer. Figure 1 illustrates a typical failure mode in at a cross-section of the dike on the left bank of the Kushiro River between stations 9K400 and 9K850. The failure mechanism illustrated in Fig. 1 is adapted from Sasaki et al. (1995). In 1994, a major earthquake occurred off the west coast of Hokkaido, the Nansei-oki earthquake, which caused failures of flood protection dikes along several river basins in western Hokkaido. After these earthquakes, the Hokkaido Development Bureau initiated a program of improving the diking systems. Because of the great length of dikes, they wished to develop a criterion for prioritizing the remediation work. One of the approaches they adopted was to use potential crest settlements as a criterion.