The total ice force acting on offshore pile structures, located in cold regions, has already been investigated by many researchers. Few papers, however, have described the distribution of ice pressure on the structures and the failure mechanics of ice sheet. It is necessary to study them in order to design the pile structures, keeping in mind safety and economic factors. The results of our experiments on failure mechanics of an ice sheet are useful for dynamic analysis. For analysis of stress and, especially, local buckling of structures, it is essential to examine the distribution of ice pressure acting on the structures. This paper describes a systematic study of these aspects through field tests with three rectangular piles (20, 40, 60 cm in width) in Saroma Lagoon in Hokkaido, Japan’s northernmost island, to clarify the effect of aspect ratio. It is clear from our experiments on ice pressure that the distribution of ice pressure can be classified into two types according to the strain rate ε˙ (= V/4B, V: penetration velocity of piles, B: pile width) defined by Michel and Toussaint [1] in each aspect ratio, B/h (h: ice thickness). It is our hypothesis that the failure periods of ice sheet are determined by the aforementioned strain rate and the aspect ratio.