1 Abstract—Increasing population growth requires more sustainable development of energy. This non-contaminated energy has an inexhaustible energy source. One of the vital parameters in such structures is the choice of foundation type. Suction caissons are now used extensively worldwide for offshore wind turbine. Considering the presence of a number of offshore wind farms in earthquake areas, the study of the seismic behavior of suction caisson is necessary for better design. In this paper, the results obtained from three suction caisson models with different diameter (D) and skirt length (L) in saturated sand were compared with centrifuge test results. All models are analyzed using 3D finite element (FE) method taking account of elasto-plastic Mohr–Coulomb constitutive model for soil which is available in the ABAQUS library. The earthquake load applied to the base of models with a maximum acceleration of 0.65g. The results showed that numerical method is in relative good agreement with centrifuge results. The settlement and rotation of foundation decrease by increasing the skirt length and foundation diameter. The sand soil outside the caisson is prone to liquefaction due to its low confinement. Keywords—Liquefaction, suction caisson foundation, offshore wind turbine, numerical analysis, seismic behavior. I. INTRODUCTION NE of the most vital concerns of humans is the environmental pollution. This pollution is caused by several factors, and one of the most important factors is the fossil fuels. Offshore wind energy, as a green and renewable energy, can be a safe alternative to other energies like fossil fuels [1]-[3]. Offshore wind power, one of the most promising sources of renewable and clean energies, has been utilized for decades on a large scale and has developed rapidly in the world [4]. The first of offshore wind farms was built in Denmark in a shallow depth of water (between 2-4 m) [5] after that it was developed in other countries. Two common types of foundations for offshore wind turbines are gravity base and large diameter mono-pile foundations [4], [6]. These two foundations are mostly used for water at low depths. Mono-pile foundations are used for depths below 30 meters, and the gravity base foundations are used up to 40 meters in depth [2], [7]. One of the ways to generate more wind energy is to install wind turbines in the deeper water. In order to achieve this goal, suction caissons are the best alternative to traditional foundations. Suction caissons are the cylindrical and hollow large structures made of steel or concrete with an open bottom and closed top and Mohsen Saleh Asheghabadi is with the Department of Civil Engineering, Tsinghua University, Beijing 100084, China (corresponding author, phone: 10-627-93001; fax: 10-627-93001; e-mail: mos16@mails.tsinghua.edu.cn). Alireza Jafari Jebeli is with the Chair of Foundation Engineering, Soil & Rock Mechanics, Ruhr-Universität Bochum (e-mail: alireza.jafarijebeli@rub.de). also usually there are several holes on the top for suction [8]- [10]. The use of suction caisson has several advantages, such as high installation speed, no need special and large equipment for installation do not create noise during drilling, and can easily be destroyed at the end of service [11]-[13]. In the design of the suction caisson, several factors such as type of soil, type and load intensity, L/D (length of skirt (L) to diameter of suction caisson (D)), marine and construction conditions are effective. L/D is one of the most important factors affecting the behavior of suction caisson. Generally, the maximum L/D for suction caisson is 8 which is very small compared with a pile foundations which is about 60 [14]. Considering that some of the offshore wind farms are located in earthquake areas, the study of seismic behavior of suction caisson is one of the most vital engineering issues. Liquefaction is one of the phenomena that may occur during an earthquake and cause wind turbine structure destruction [15]. Investigation of seismic response of a turbine can be another important issue in the study of seismic behavior of suction caisson [16]. The acceleration response in both free- field and near suction caisson should be investigated, as it may cause pore water pressure and deformation of soil which ultimately affect the function of the foundation. In the current research, the results obtained from the numerical method performed by the 3D FE software of ABAQUS [17] have been compared with the results of centrifuge test. This method can be used in the absence of an earthquake in situ, which is actually an appropriate alternative to prototype and real situations. Numerical method is another way to study the seismic behavior of suction caisson which can be done with various software. In this study, three models of Toyoura sand [18] soil and suction caisson with different dimensions have been used. In all the analysis, finite element method (FEM) [19], [20] is used and the results of them in different points of model by considering the interaction between soil and foundation are performed and compare with results of centrifuge test [21]. Dimension of suction caisson foundation (aspect ratio D/L) has different effects on the seismic behavior of suction caisson so in order to investigate this issue three different suction caisson have been chosen. In all models, a 1D earthquake with a dominant frequency of 1 Hz was used [21], [22]. In most studies, this earthquake has been used [23]. Generally, after comparing the results obtained from different models, we conclude that increasing the diameter of the suction caisson is one of the best ways to reduce the seismic response of the whole system. In recent years, a few numerical and experimental studies have been carried out to survey this issue. Reference [24] has analyzed 3D dynamic behavior of suction caisson under earthquake loads. In this study, nonlinear soil behavior with Seismic Behavior of Suction Caisson Foundations Mohsen Saleh Asheghabadi, Alireza Jafari Jebeli O World Academy of Science, Engineering and Technology International Journal of Geotechnical and Geological Engineering Vol:13, No:2, 2019 30 International Scholarly and Scientific Research & Innovation 13(2) 2019 ISNI:0000000091950263 Open Science Index, Geotechnical and Geological Engineering Vol:13, No:2, 2019 waset.org/Publication/10010000