Experimental observations on the ice pile-up in the conductor array of a jacket platform in Bohai Sea

Abstract

Massive ice pile-ups have been frequently observed in the conductor array of offshore jacket platforms in Bohai Sea. Once formed, such rubble piles were very difficult to clear manually and therefore studies on the ice rubble piles and their forming process were needed. This study investigates the ice pile-up behavior in the conductor array of a jacket platform in Bohai Sea by conducting a series of model tests in the ice tank at Tianjin University. The laboratory-scale model jacket was mounted on a rigid carriage and towed through the ice sheet at different speeds, directions and water levels. Observations on the test phenomena indicated that the water level and ice attack direction had a significant influence on the ice failures in front of the ice-breaking cones and the conductor array, thereby resulting in different ice pile-up patterns in the conductor array. The ice drift velocity only affects the pile-up dimensions, normally higher ice velocity resulting in higher pile-up heights. Also, based on the measured ice pile-up dimensions, the distribution of the ice rubble pile in the conductor array was found to be non-homogeneous, both laterally and longitudinally, and the rubble pile was found “grounded” on the bottom of the model conductor array in some cases, which might bring about additional load to the jacket structure. Furthermore, the horizontal ice forces acting on the conductor array due to ice rubble building were also measured, and comparisons of the ice forces based on the present tests with the calculated results from ISO algorithm were made. The R value of 5–6 might be more applicable for the present structure under the present ice conditions.