Capacity Characteristics Of Clustered Suction Piles In Soft Clay

At present, our country’s offshore platform mainly concentrated in the shallow-water area. The traditional platform structures were widely used in these regions, such as tension leg platform and gravity platform. The platforms are subjected to wind load, wave load and vertical load. With the exploitation of offshore resources such as oil and natural gas, the offshore geotechnical engineering has developed into deep-water of extra-deep-water. Compared with shallow-water region, deep-water field has plenty of saturated soft clay foundation, the platform structures are no longer subjected to vertical downward load, but the uplift load and lateral load. And the wave load and wind load are neglect for the foundation in deep-water. Due to the factors such as the weak foundation and difficult of installation the traditional offshore platform structure and foundation forms are no longer applicable. The application of semi-submersible structure and large floating structure, and then the large anchorage problems for offshore geotechnical engineering brings some new challenges. Recently, a new type of offshore platform foundation form suction pile is developing at home and abroad. It is suitable for soft and very soft clay, make the transportation and installation convenient, reduce the cost and especially has perfect bearing capacity and stability. All of these characteristics make suction pile become optimization foundation form for deep-water platforms. The suction pile has two forms, one kind is single pile; the another kind is clustered suction piles which are made up by three combination of single suction piles. The present studies have been focused on single suction pile. However, with the development of offshore activities into deeper water field, the requirement of loading capacity of single suction pile is increased and the design size should be required in a larger size. This make it difficult to transport and install. In order to improve the capacity to reduce the costs, the clustered suction piles should be presented and make more researches. In this paper, a large general finite element analysis software ABAQUS was used to analyze the capacity characteristics of single and clustered suction piles.This paper, based on the a large general finite element analysis software ABAQUS, established a finite element analysis model of single and clustered suction piles on the soft clay under lateral and vertical loading. According to the finite element analysis, when the uplift load is slowly exerted suction piles present a kind of local shear failure mode——the pile and soil are separated with the pile body pulled leaving the soil plug outside. On the other hand, when the uplift load is exerted rapidly, piles present a kind of general local shear failure mode——the suction is produced in the internal of the pile and soil plug is pull out with the pile body. Compared with single pile, the increase of build-up capacity of the clustered suction piles is obvious. When the clustered suction piles are applied under horizontal load with considering the active soil cracks, the soil form a passive side wedge at the back of suction pile due to the effect of group pile. When the active soil cracks is not considered, the clustered suction pile presents a kind of double failure mechanism. Compared with single suction pile, the lateral loading capacity of clustered suction piles is greatly improved and the displacement distribution is more uniform.Through the comparisons of variable parameter calculation, this paper has discussed the influence of loading attachment point, loading angle and soil property on ultimate loading capacity of clustered suction piles.