ジャッキ・アップ・リグを支持する海底地盤の安定性に関する模型実験

概要

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Foundation failure has been the main cause of several jack-up accidents ranging from total loss of lives to a varying degree of damage to the structure and the drilling equipments. In addition, it can be anticipated that sea bottom soil will restrain the rotational movement of spud tanks, which means the overturning moment can be partly shared by the sea floor. This is very important concept in designing the unit and for their safety assessment but little are known on this matter due to very complicated and uncertain behaviour of the units. The behaviour of soil under spud tanks, however, is extremely complicated depending on soil condition. Ioading pattern and shape of spud tanks etc. . In this experimental study, authors performed model tests by 4-legged rigid rig model and half-circular footing model. Several points are confirmed as the followings ; (1) In case of 4-legged platform, the skew direction of horizontal force gives more critical condition than beam direction. (2) About 25% of overturning moment is shared by reacting moment of soil in case of 4-legged model. (3) Failure patterns of soil under footing are observed but for inclined load not in good agreement with Hansen's slip line. (4) Hansen's formula gives conservative estimation of bearing capacity ratio for eccentric and/or inclined load.
社団法人日本船舶海洋工学会の論文