Research and Design of Caisson Platform with Underwater Piles Used in Shallow Water

Because of its proven technique and high security, jacket platform is the most popular fixed offshore platform in shallow water. However, the high cost and the heavy steel quantity place serious restrictions on the application of jacket platform in marginal oilfield. Research on cassion plarform with good resistance to ice load and vibration, has been carried out.In view of specific environments and requirements, fuzzy optimization selection method which is based on priority has been applied to cassion platform in service, and then the basic platform structure with satisfactory adaptability to marginal oilfield has been selected. In addition, some improvements on the selected platform structure have been made, and cassion platform with three piles that adapts the environments of Chengdao area and meets the requirements of target project has been achieved.Cassion platform has the feature of simple structure and less redundant members. In light of the nonisotrophies, uncertainties and fuzzinesses, reliability analysis of cassion platform members has been carried out. And then, cassion platform has been analyzed by fuzzy optimal method, so that optimal structure system with rational reliability could be accomplished.After the fuzzy optimization of cassion platform structure, detailed analysis of cassion platform has been executed by means of professional software SACS. Meanwhile it has completely comformed to associated codes and standards from API, AISC and DNV. The results of the analysis indicate that the global capability and stability of cassion platfrom meet the requirements of the associated codes.The underwater connection of supporting pile and cassion foundation is the key part of cassion platform. The underwater pile heads is connected by mechinal intermeshing. This method can provide reliable connection both in service phase and installation phase, and it can be implemented with little risk. The pile is connected to cassion foundation by underwater grouting annulus space with PAE sand cement slurry.Grouting packer has been designed. It is simple, reliable and applicable to underwater grouting seal.