RIASSUNTO
ABSTRACT
Ice floes are widely known to abrade surfaces of structures constructed in sea water areas where ice floes move actively. According to Janson''s research (1987) t) on concrete lighthouses in the Gulf of Bothnia, where sea ice movements are intense, the abrasion depth of several lighthouses was approximately 140 mm (approximately 7 mm per year). Also, since both corrosion and abrasion by sea ice cause a decrease in the thickness of the steel of marine structures in frozen sea water areas, differentiating these effects is difficult in practice. The development of oil fields is just underway near northern Sakhalin in the Sea of Okhotsk. Sea ice is active in this area, Composite structures, in which the surfaces of structures are coated with steel, are believed to be effective for the future design of structures in frozen sea water areas. Hence, predicting the abrasion depth of surface steel due to sea ice movements is important for the design of these structures. The area of our research was the water channel constructed in December, 1978, for the No. 2 estuary of Saroma Lagoon in Hokkaido, Japan. The channel connecting the lagoon with the Sea of Okhotsk is 50 m wide, 260 m long, and 5.0 m deep. We measured thickness of the steel sheet piles used for the side walls of the channel and for the piers of the bridge built over the channel. From the measurements we found the abrasion of the steel by sea ice movements and developed a technique to estimate the abrasion depth.
1. LOCATION OF FIELD SURVEY AND METHOD OF STUDYING ABRASION
The No. 2 estuary of Saroma Lagoon was constructed in 1978 with two purposes; they are to improve the seawater quality within the lagoon and to make the estuary navigable.