Dissertation > Astronomy,Earth Sciences > Oceanography > Ocean Engineering

Behavior of Installation and Seepage Law of Offshore Skirted Suction Foundation for Offshore Wind Turbines

Author LiuXiaoLi
Tutor LiDaYong
School Shandong University of Science and Technology
Course Geotechnical Engineering
Keywords ocean engineering skirted suction foundation finite element method suction penetration penetration resistance seepage field hydraulic gradient
Type Master's thesis
Year 2011
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Suction foundations are also referred to as suction anchors, suction piles or suction caissons, and are usually wide open at the bottom and close at the top steel cylinder structure, can withstand the tremendous horizontal load and bending moment. Due to the cost of the economy, construction convenient and reuse, etc., suction foundations are conventionally used in offshore engineering to fix platform and moor floating structures. Currently they act extensively as foundations for the offshore wind turbines in shallow sea water. Such a foundation is suffering from large lateral cyclic loading and moment resulting in the excessive horizontal displacement and rotation. In addition, due to the erosion of seabed caused by waves, the bearing capacity for the suction foundation will be decreased. To mitigate these disadvantages, a new type of suction foundation named the skirted suction foundation is presented in this paper. This new type of suction can significantly improve the resistance to the sea-bed erosion and supply bearing capacity. Houlsby’s approaches to analyzing the installation of conventional suction anchors in sand, in clay and layered materials (sand over clay) are extended to the skirted suction foundation. The two stages of the penetration of the skirted suction foundation consisting of self weight induced and suction induced are investigated. Compared with the installation of the conventional suction foundation depicted in the literature, it is shown that the skirted suction foundation has a better behavior of installation with lower cost of construction and further time saving.Through analytical calculation for penetration and the numerical simulation of seepage field, the main investigations and conclusions consist of the following Parts:(1) In the saturated sand, clay and layered materials (sand over clay), the skirted suction foundation can be installed to the needed penetration depth successfully. The conclusions mentioned above proved the suction skirted foundation has a good penetration performance.(2) In this paper we present the calculation procedures that are required for suction caisson installation in sand soils, clay and layered soils. Comparisons among these results and comments are made herein, the process of suction penetration in layered soils is far more complicated than in sand or clay.(3) To investigate the feature of seepage fields during the suction penetration of the skirted suction foundation, the seepage field correspondent to different suction pressure can be simulated by changing the boundary conditions based on the general-purpose finite element software PLAXIS. It is addressed that the regulations of seepage field at one time are uniform during installation and the fluid fields are influenced by soils parameters and permeability.(4) The scope of this paper is to consider the calculations appropriate for the installation of caissons in sands, clay and layered soils. Calculation methods are presented for determining the resistance to penetration of open-ended cylindrical caisson foundations both with and without the application of suction inside the caisson. Comparisons are made with case records. Then, this paper adopts finite element method to carry out the calculation and analysis to the suction penetration field of the skirted suction foundation. Through analysis to the result data of practical examples, some satisfactory regulation could be obtained to support the design and construction of the skirted suction foundation. The conclusions mentioned above proved the suction skirted foundation has a good penetration performance. It shows that the suction skirted foundation is very practical in use.

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