The Distribution of Ice Pressure on Offshore Pile Structure and the Failure Mechanics of Ice Sheet

Abstract

ABSTRACT The total ice force acting on offshore pile structures, located in cold regions, has already been investigated by many researchers. However, few papers 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 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 ë (= v/4B, v: penetration velocity of piles B: pile width) defined by Michel and Toussaint in each aspect ratio, B/h (h: ice thickness). It is our hypothesis that the failure periods of ice sheet are determined by the strain rate and the aspect ratio mentioned above. INTRODUCTION In order for exploration and production in the oil begins of the offshore Arctic to be possible, it will be necessary to build structures capable of withstanding forces caused by the movement of the surrounding ice sheet. It is important to explain the interaction between the structures and the ice sheet so that they may be designed more rationally. Total ice force acting on the structures has previously been discussed, mainly in regard to the interaction. However, they can't be properly designed only on the basis of the total ice force. Stress analysis of local buckling on structures, especially those having a large diameter and thin wall, should be carried out. The equation for the total ice force acting on the structures, arrived at by the authors, can be expressed as follows:(Mathematical equation available in full paper) If local buckling occurs at the area of contact with the ice sheet, the value of the above shape factor, namely C, will increase and the total ice force is considered to become larger. The distribution of ice pressure must be obtained in order to examine whether or not local buckling occurs on the wall of the structures. Moreover, the structures are severely damaged by the interactive interference between them and ice sheet. In fact, the marine lighthouse in the Bosnia Sea has received such damage. Dynamic analysis through numerical simulation should be carried out in order to prevent structures from receiving this damage. Maattanen, and Matlock et al. have studied the above problem, however, few papers have been issued, which describe the dynamic analysis from the perspective of failure periods and failure modes of ice sheet.