Kunihiko Ishibashi

A FIELD INVESTIGATION ON THE DAMAGE OF COASTAL, PORT AND HARBOUR FACILITIES CAUSED BY THE NIIGATAKEN CHUETSU-OKI EARTHQUAKE IN 2007

A field investigation has been carried out to investigate the damage of coastal, port and harbour facilities caused by the Niigataken Chuetsu-oki Earthquake in 2007. The instrumental JMA seismic intensity of a strong 6 was registered in Kariwa village, Kashiwazaki and Nagaoka cities, in Niigata, Japan. The damages to coastal, port and harbour facilities were investigated. The old seawalls at Osaki coast in Kashiwazaki were broken due to strong seismic motions. Several coastal facilities ware partly broken due to liquefaction occurred by the severe ground shaking. The corners of concrete caissons used for a breakwater were broken off due to strong collisions. There are many old woods appeared on a sea bottom surface after the earthquake in the region offshore from Izumozaki town to Kashiwazaki city. The woods might appear to floating up to the sea bottom surface due to the liquefaction of sea bottom sediments.

FIELD OBSERVATION OF WAVE OVERTOPPING RATE AND SPLASH HEIGHT OVER BLOCK MOUND SEAWALL

Field observations have been carried out to investigate on splash height and overtopping rate of block mound seawall at the Oyashirazu Coast in Niigata Prefecture. Splash heights were measured by using video camera system. Velocities and depths of a overtopping flow ere directly measured by electro-magnetic urrent meter and ultrasonictype elevation meter. The main results are in the followings: Relative heights of a splash depend on the relative crown height (hc/Ho) and deepwater wave steepness. They increase their values as the relative crown height become large, whereas the deepwater wave steepness become small. Standard deviations of splash height amount to about 25% of the mean value. The maximum velocities of overtopping flow reach from 6m/s to 8m/s with a depth of 5cm to 20cm. The peak values of overtopping rate measured amount to larger than 0.2m3/s/m.