Suction caisson foundations, also known as skirt piles and bucket foundations, have been used with success in the North Sea for major structures such as the Gulifaks C (1989) gravity platform, the Europipe fixed steel jacket (1994), and the Snorre (1991) tension leg platform. Insufficient experience in the US with this novel foundation type prompted Shell Oil, in 1993, to utilize conventional pile driving for the Auger platform in the Gulf of Mexico (GoM). World events and the discovery of major petroleum prospects in the deep GoM, within the United States Exclusive Economic Zone, make it necessary to examine and exploit the new technology for application within this zone. The thrust of this effort is in line with the stated objectives of the Offshore Technology Research Center and our industry partners; specifically the study of the basic engineering problems associated with reducing the costs and improving the structural reliability of structures in water depths of 6000 to 10,000 ft. in the GoM. The main objective of the research has been to study the behavior and pullout capacity of suction caisson foundations. An experimental approach was used in which model caissons were tested under static and cyclic pullout loading. Prior to testing, the program involved the preparation of soil samples, design and manufacture of model suction caissons, and the development of instrumentation, data acquisition, and loading systems. The caissons were made with length-to-diameter ratios of 2, 4, 6, and 12 to study the effect of increasing caisson length on penetration resistance and pullout capacity, as well as the feasibility of using suction as the method of installation. The simulated TLP loading was in the form of static and cyclic tension. Measurements of total foundation capacity, displacements, and pore water pressures inside and in the vicinity of the model caissons were made. The pullout capacity of the model caissons was clearly defined under both drained and undrained loading conditions. Results of the experimental program have shown that the rate of pullout loading had a significant influence on the capacity. The long-term pullout capacity represented the upper limit on peak cyclic loading.
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