ABSTRACT

The effect on ice load of the initial shape of an ice sheet's leading edge is shown through field ice indentation tests using natural freshwater lake ice. The shape of the leading edge of natural sea ice near a bluff in the harbor is also measured to determine its surface roughness. Under the test condition here, the results show that subsequent ice load rather than first prominent peak ice load is likely to control the ice load on a structure in the real world. Furthermore, the shape of the leading edge of natural sea ice after an ice indentation test is measured to evaluate the actual ice/structure contact area during the subsequent ice load, and in turn to estimate the nature of the contact during subsequent (potential) local ice sheet failure.

INTRODUCTION

Ice loads on offshore structures were evaluated in the early stages of ice load research, based on the assumption of uniform contact between ice sheet and structural face. Under the idealized contact of a model structure with an ice sheet, the ice load depends on an effective ice strain rate (dε/dt) calculated by V/(2W) or V/(4W) (where V is the relative velocity of the ice and the model structure and W is the width of the model structure). It was reported that ice load as well as ice strength are a maximum value in the order of 10–3 (s–1) of effective ice strain rate (V/(4W)) (Saeki, 1978, 1980). Under the conditions of both idealized contact and the order of 10–3 (s–1) of effective ice strain rate (V/(4W)), ice load in a field ice indentation test shows a first prominent peak (maximum) due to uniform contact, and then ice load (called subsequent ice load) fluctuates, showing peaks due to nonuniform structure/ice sheet contact.

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