ABSTRACT
Suction caissons are frequently used on a variety of offshore structures and at present they are considered as a foundation for floating wind turbines. However, no systematic study on floating wind turbine foundations is reported for the northern region of South China Sea. To bridge this gap, the current research is performed on the large deformations for bearing capacity of suction caisson in marine clay for southern part of China Sea. In this work, a two-dimensional axisymmetric finite element model (FEM) is established to study the behaviour of suction caisson foundations relative to the marine soft clay under undrained conditions against the pull-out loading by using commercial software ABAQUS/EXPLICIT. The Arbitrary Lagrangian-Eulerian (ALE) technique is adopted to simulate the large deformation of soil caused by pull out of anchors. The studied parameters include uplift loading, load point, cohesion, soil/caisson geometry and initial stress state (Ko). The friction contact interface and contact surfaces are the considered parameters for soil-caisson interaction. The variations in friction angle of soil along the Soil/Caisson surface are measured and present the rising effect on the pull-out capacity. The pull-out force with displacement curve is obtained by the finite element modeling. It is found that the pull-out capacity of suction caisson finite element model shows an increase trend with an increase in friction angle (θ) of soil. Conclusively, the measured parameters are helpful for the effective and reliable geometry design of offshore wind turbine foundations.
Suction caisson foundations are considered to be the most favorable and alternative foundation for offshore wind turbines structures (Senders 2009, Liu et al. 2015, Yu et al. 2015, Liu et al. 2016). Suction caisson is recognized as an economical and reliable foundation and has several advantages over other conventional foundations such as easy installation, cost-saving and high positioning accuracy (Aspizua 2015, Feng et al. 2016). Several investigations and research conducted on the suction caisson and verified that the suction caisson foundation is realistic for numerous soil conditions at different water depths from shallow to greater water depth (Ibsen et al. 2014, Jia et al. 2018). As the use of suction caisson foundations are rapidly increasing recently, the design of suction caisson foundations become a key challenge for the geotechnical industry (Jin et al. 2019). A future challenge for the wind turbine industry is the frequent use of floating offshore wind turbines as the cost of conventional foundations for fixed platforms rises rapidly with the increase of water depth in far offshore (Blanco 2009). Floating offshore platforms lately involved for deep water locations as it moored to the seabed using suction caisson, driven piles or gravity platforms (Stevens and Rahim 2014). Many researchers proposed various floating wind turbine foundation concepts to simulate these foundations and their estimation for load bearing capacity (Sebastian and Lackner 2013). Moreover, soil-caisson interaction (SSI) plays a vital role in the simulation and designs of suction caisson (Arany and Bhattacharya 2018). Therefore, it is necessary to evaluate the load bearing performance of suction caisson foundations for floating wind turbines. Limited studies were carried out on the finite element modeling of suction caissons to measure the pullout capacity in clay for offshore wind turbine foundations (Zhu et al. 2014, Cheng and Wang 2016, Sawicki et al. 2016). However, still there is a research gap for particularly floating offshore wind turbine structures. Though, no systematic study exists on the floating offshore wind turbines situated in the northern part of South China Sea.
