Mechanical Model of Ice Gouging on Sloping Sandy Beach
Shinji Kioka, Hitachi Zosen Corp., Japan
Yuriko Terai, Nikken Consultants Inc., Japan
Natsuhiko Otsuka, North Japan Port Consultant Co., Ltd.
Akifumi Nishihata, Department of Civil Engineering, Hokkaido University, Japan
Hiroshi Saeki, Professor, Department of Civil Engineering, Hokkaido University, Japan
Keywords: ice gouging, sea ice, drifting ice
Abstract
The coastal area facing the sea of Okhotsk in Hokkaido is annually covered with drifting ice. When these ice floes with a deep draft move toward the shore, they gouge sandy sea bottoms. Due to this ice gouging, marine resources along the shallow sandy coast are damaged, for example, seashells, buried strictures and pipelines. In this study we describe the mechanism of ice gouging and obtain basic knowledge necessary to take preventive measures in future against damage by ice floes.
1. Introduction
When ice floes attached to the sea bottom of a shallow water area are moved to a shallower area by being pushed by an offshore ice field, they gouge the sandy bottom, a process called ice gouging. Reports exist of damage caused by this action of ice. For example, caseshave been reported of some marine resources, such as sea urchins, being carried onto the shore while others were crushed to death by the weight of the sea ice itself also buried stnictures have been damaged. To clarify the mechanism of ice gouging, we conducted a study of this ice action from experimental and theoretical bases, using a simple mechanical model. In our previous experiments, ice models of a rectangular parallelepiped were used, but the model ice used in this study was trapezoid in shape with a sloped front, similar to an actual ice floe, to use to study how ice forces acting on the sandy sea bottom change and how gouged surfaces change. This study was to not only understand the mechanism of ice gouging, but also to have a basic knowledge of how to take preventive measures against the kind of damage mentioned above.
2. Experimental Method
Fig-1 shows the devices used in the experiment. The bottom of a water tank was covered with sand and were inclined at 1/10 or 1/5. The bottoms were inclined steeply to make the model ice gouge more clearly, although in reality an ocean bed has a gentler slope. The sand used in the experiments is described later. An oil jack with a stroke moving up to 50cm horizontally was fixed to one end of the tank, then the model ice (described later) was installed in the front of the oil jack and was pushed in a horizontal direction at velocities of 0.4cm/s.
0.9cm/s and 1 .7cm/s. The connector FREE, whose force of constraint acting on the vertical direction is rather weak, was set between the oil jack and the model ice, and a load cell was set between the FREE and the jack. Then the ice forces were measured by the load cell (the pushing force with the jack). At the same time, the horizontal distance from where the model ice began to move, i.e. gouging distance, and the gouging depth carved by the ice, were measured. Here, the ice made a small rotational motion; we regard this ice movement as approximately
