To estimate the ice load exerted on offshore structures in an icecovered sea area, understanding the strength characteristics of the sea ice is necessary. In this paper, the strength of the first-year sea ice at Notoro Lagoon in Hokkaido, Japan, is discussed in terms of mechanical properties (compression o c, bending o b, tensile o t and shear ~:), correlation of those properties and statistic characteristics. The ratios of each strength to compressive strength are as follows. The compressive strength ranged from 0.5 to 3.0 MPa and r / o c=0.31, a b/o c=0.27, a t/tr c=0.17. It is considered that the distribution determined in the experiment well follows a log-normal distribution (three population parameters) or a Weibull distribution (three population parameters).
A correct estimation of ice loads is necessary when making a basic design of offshore structures built in an ice-covered sea area. In particular, the basic strength (compressive, bending, splitting tensile and shearing) of ice sheets needs to be known to closely examine the fracture strength properties of ice sheets at the exact moment an ice sheet collides with a vertical wall structure (Figure 1). In this report, we summarize the results obtained in three winter seasons from 1996 through 1998 regarding the physical properties and basic strength of the fu'st-year ice used in the indentation tests made by the Japan Ocean Industries Association at Notoro Lagoon in Hokkaido on the coast of the Sea of Okhotsk. Correlations between each strength and compressive strength, statistical characteristics of compressive strength, and the dependence of compressive strength and shearing strength on the strain rate are clarified.
Figure 2 shows the relationship between density and salinity of sea ice. We measured density : weight/volume with the compressive test specimen.
