On Ultimate Bearing Capacity Of Jack-up With Square Spudcan And Application To Structure Investigation Against Punch-through

Jack-up platform is widely used in the offshore exploration in China. Owing to the complicated subsea geological condition, punch-through accidents occur frequently, which threaten the operation safety of Jack-up.In this paper, in-depth theoretical study for the ultimate bearing capacity assessment for Jack-up platform with square spud-can is carried out. In addition, methods of preload prediction and structure response assessment during Jack-up punch-through are discussed. The main contents are as follows:1、For the ultimate bearing capacity of square spud-can in single soil layer, slide failure surface for the3D soil is created and a new ultimate bearing capacity expression is obtained from the static equilibrium conditions of plastic body based on the ultimate balance theory.2、A reasonable assumption is presented for the failure surface of double-layer foundation based on the analysis of Meyerhof-Hannah punching theory. Then one new method for calculating the ultimate bearing capacity of double-layer foundation is developed.3、In order to predict the risk of punch-through more precisely, one new method-dynamic analysis method is proposed and the result by this method is found to be more accurate, so that the Jack-up punch-through can be avoided effectively.4、To analyze the structure response of Jack-up in punch-through accident, a detailed finite element model is built. The status of leg and hull before and after punch-through, distribution of dangerous points, effects of punch-through speed on the structure and change of preloads are studied in three working conditions. The response characteristics of Jack-up in the accident are investigated and an ultimate punch-through depth is found out to determine the structure ability against punch-through.