The Coefficient of Friction Between Sea Ice and Various Materials Used in Offshore Structure

Abstract

ABSTRACT When structures having inclined surfaces, such as cone type and inclined pile structures, are constructed in coastal and offshore cold regions, sea ice pressure must be considered in their design. In order to estimate this ice pressure, the relationship of the coefficients of static and kinetic friction between sea ice in various conditions and construction materials must be clarified. The authors have been conducting, for four years, coefficient of friction experiments between sea ice and various commonly used offshore construction' materials such as concrete and steel. These coefficients have been found-to be affected by the following:relative velocitysea ice temperaturesurface roughness of construction material They have been found to be relatively unaffected by the following:contact areavertical stressgrowth direction of sea icewater in the sea ice interface INTRODUCTION In recent years, the development of sea bed resources and the industrialization of cold regions have led to hydraulic structures such as oil drilling platforms being constructed in coastal and offshore areas exposed to sea ice pressure. The minimization of this sea ice pressure induced stress upon these hydraulic structures is obviously important. Also of importance is the frictional resistance of floating sea ice to ice-breaking ships. Since fracturing of the sea ice is more easily induced by bending rather than compressing it, inclined pile and cone type structures are usually considered more efficient. In this case, the relationship of the coefficients of friction between sea ice in various conditions and construction materials must be clarified. Experiments were conducted using various construction materials in order to clarify the effects of the following:contact areavertical stressgrowth direction of sea icevelocity of test specimen relative to the sea icewater in the sea ice interfacesea ice temperaturematerial's surface roughness TESTING METHOD AND APPARATUS 1. Experimental Apparatus A diagram of the experimental setup is shown in Fig. 1. The apparatus was designed with due consideration of the following:use of various construction material test specimensvariable vertical stressuse of variously sized sea ice samplesvariable relative velocitysubmersion of test interface 2. Testing Procedure A horizontally movable-test platform was used. The platform was powered by a hydraulic jack. On this platform, various construction material test specimens were securely placed. The sea ice sample was then placed upon the test specimen; the coefficient of friction exists in the interface. Static vertical loading was accomplished by placing weights on the steel cap protecting the ice sample. The sea ice sample remained immobile relative to the test bad. The relative velocity between the ice sample and test specimen was controlled by varying the hydraulic pressure applied to the jack. Since ice is a visco-elastic solid, the coefficient of static friction varies with the duration of the loading time. Therefore, in these experiments, the horizontal velocity was initiated within 10 seconds after the application of the vertical load.