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Upper bound mesh and deformation patterns for caisson foundations of L=D ¼ 1.0 and L=D ¼ 0.5 at different ultimate states (Points A, B, C, and D, E, F in Figure 7).
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Determining the ultimate capacity of suction caissons in response to combined vertical, horizontal and moment loading is essential for their design as foundations for offshore wind turbines. However, the method implemented for stability analysis is quite limited. Numerical limit analysis has an advantage over traditional limit equilibrium methods a...
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Context 1
... upper bound analysis shows that different failure mechanisms prevail at different points on the failure envelope. Figure 9 plots the specific failure mechanisms. If the moment dominates, then the failure mechanism is a rigid body rotation with its center located at a certain depth under the cap (Points A and D). ...
Context 2
... plastic zone represents clay failure in the upper bound analysis. Figure 9 clearly shows that caissons with larger embedment ratios take great- er advantage of deep-level clay, resulting in a deeper plastic zone and a larger bearing capacity. The magnitude of the lat- eral load mainly affects the plastic zone horizontally and that of the overturning moment affects the zone vertically (compare A with C or D with F). ...
Citations
... The geotechnical design of suction caisson foundations for offshore wind applications requires several key design considerations (Sturm 2017), including estimations of foundation capacity (e.g., Samui et al. 2011;Liu et al. 2014;Bagheri et al. 2017; Barari et al. 2017;Wang and Cheng 2016;Ukritchon and Keawsawasvong 2016;Yang et al. 2018;Nielsen 2019;Gelagoti et al. 2019;He at el. 2021;Wu et al. 2022;Liu et al. 2023) for ultimate limit state assessments, installation analysis (e.g., Houlsby and Byrne 2005a, b;Anderson et al. 2008;Senders and Randolph 2009), estimations of displacements and tilt under monotonic loading (e.g., Suryasentana et al. 2018Suryasentana et al. , 2019Suryasentana et al. , 2023b, seismic loading (e.g., Kourkoulis et al. 2014;Esfeh and Kaynia 2020;Antoniou et al. 2022) and cyclic loading (e.g., Foglia et al. 2014;Skau et al. 2018Skau et al. , 2019Zhu et al. 2018Zhu et al. , 2019Byrne et al. 2020;Yin et al. 2020) for serviceability limit state assessments, and estimation of the stiffness of the caisson response for natural frequency and fatigue limit state assessments. Previous studies (e.g., Latini and Zania 2017;Jalbi et al. 2019) have shown that the dynamic stiffness of the caisson response affects the eigenfrequency of vibration of the offshore wind support structures and thus, their fatigue life. ...
The static stiffness of suction caisson foundations is an important engineering factor for offshore wind foundation design. However, existing simplified design models are mainly developed for non-layered soil conditions, and their accuracy for layered soil conditions is uncertain. This creates a challenge for designing these foundations in offshore wind farm sites, where layered soil conditions are commonplace. To address this, this paper proposes a multi-fidelity data fusion approach that combines information from different physics-based models of varying accuracy, data sparsity and computational costs in order to improve the accuracy of stiffness estimations for layered soil conditions. The results indicate that the proposed approach is more accurate than both the simplified design model and a single-fidelity machine learning model, even with limited training data. The proposed method offers a promising data-efficient solution for fast and robust stiffness estimations, which could lead to more cost-effective offshore foundation designs.
... Chen and Randolph 2007;Houlsby et al. 2005), numerical simulation (S. R. Kim 2012;Qi et al. 2022;Vulpe 2015), and limit equilibrium theory (Hu, Randolph, and Watson 1999;Wang and Cheng 2015). A lot of research has also been carried out on the mudmat foundation (Gourvenec 2008;Shen, Feng, and Gourvenec 2017). ...
The traditional foundation design does not consider the bearing capacity under multi-directional coupling load. However, the foundation is usually subjected to vertical (V), horizontal (H) and moment (M) loading simultaneously on the seabed. The present study examines the undrained multi-directional bearing capacity of hybrid subsea foundation in saturated soft clay using finite element analysis. The contribution of the mudmat and the suction bucket to the bearing capacity of the hybrid subsea foundation was evaluated. The results show that the suction bucket can effectively make up for the lack of horizontal anti-slip and anti-overturning ability of the mudmat. It has a significant contribution to the horizontal and moment bearing capacity. In addition, the failure envelope of bearing capacity in horizontal-moment (H-M), vertical-horizontal (V-H), and vertical moment (V-M) load space is obtained by using prescribed displacement ratio loading method. Based on the simulation results, the expression of approximate envelope of foundation bearing capacity under combined load of horizontal and moment is proposed. The study also found that a certain value of vertical load can increase the horizontal and moment bearing capacity of the hybrid subsea foundation, while excessive vertical load will lead to a decrease in bearing capacity. ARTICLE HISTORY
... To date, numerous investigations have been conducted to assess the ultimate capacity of suction caisson using model tests Villalobos et al., 2010;Zhu et al., 2013), numerical methods (Charlton and Rouainia, 2016;Kourkoulis et al., 2014;Liu et al., 2023), or plasticity theory Randolph, 1998, 1999;Wang and Cheng, 2016;Zhang et al., 2010). By contrast, the elastic stiffnesses of suction caissons have not attracted much attention. ...
The importance of accurate estimation of elastic stiffness coefficients of suction caisson has been already highlighted in previous works. Nonetheless, studies related to the spatial non-uniformity of the clayey seabed are somewhat limited, and current theoretical solutions are usually established using deterministic soil properties, overlooking the inherent uncertainty of the soil. This study focuses on the elastic performance of suction caisson in spatially random soils using three-dimensional (3D) small strain random finite element analyses within a Monte-Carlo framework. The non-uniformity of soil is mapped by modeling the shear modulus as a random field. The influences of soil profiles, embedment ratios and random field parameters on the elastic stiffness coefficients are comprehensively quantified. Results demonstrate that the spatially varying shear modulus notably alters the failure mechanism, which in turn significantly affects the elastic stiffness coefficients, ignoring soil variation will provide non-conservative predictions. To deal with the uncertainty of soil shear modulus, a series of expressions are developed by adding reliability-related parameters to the existing theoretical solutions, which can be adopted to calculate quantiles of stiffness coefficients corresponding to several given probabilities. The findings of this research may potentially facilitate the elastic performance assessment of suction caisson.
... Wang et al. [14] assessed the lateral bearing capacity of suction bucket foundation. Wang and Chen [15] focused on the suction caisson's vertical loading effect. Monajemi et al. [16] investigated the suction anchor's reaction under inclined loading. ...
Anchorage failure of a suction anchor is more likely to occur in low-strength muddy clay. This paper focuses on the failure behaviors of suction anchors and muddy clay stress responses. The centrifugal model test was used to study the loading processes of suction anchors with various pulling angles. Firstly, the multi-stage developing process of anchoring force was analyzed according to the test results. Numerical modeling was used to validate the test results. The displacement of the suction anchor and muddy clay soil were analyzed using the numerical results. Then, the numerical and testing results were compared to analyze the horizontal soil pressure responses around the suction anchors. It was found that the change in loading direction affected the distribution and development of soil stress. The horizontal soil resistance played a crucial role in improving the bearing capacity. The soil stress variation and anchor displacement revealed that the suction anchors exhibited multi-attitude coupling movement during the inclined pulling. The vertical pulling suction anchor showed shear–slip failure behaviors, while the inclined pulling suction anchors showed compression–shear–slip coupling failure behaviors. The results of this study provide insight into the interaction mechanism between suction anchors and muddy clay, serving as a reference for the design and application of suction anchors.
... Various scholars have researched the suction bucket's foundation-bearing capacity in such conditions. Wang et al. (2016) simulated a centrifuge model test and confirmed the ability of numerical limit analysis to deal with the inclined pullout capacity of suction buckets. Xu et al. (2018) derived the experimental formula for the upward movement of the suction bucket rotating point with an increasing length-diameter ratio. ...
As the suction bucket foundation is gradually applied, studying the bearing capacity of the suction bucket is particularly important for the safe operation of offshore wind power. This paper proposes a suction bucket foundation with added supports; the supports automatically extend outward through the middle pipe pile of the suction bucket to enhance its stability. The bearing characteristics of the proposed and traditional suction bucket foundations are compared. The deformation and instability characteristics of the enhanced bucket foundation under ultimate load are investigated by varying the support dimensions. The results show that the added supports can enhance the ultimate bearing capacity and the stability of the bucket foundation. When the support’s diameter remained constant while the length of the supports increased linearly from 20 to 80 mm, the vertical and horizontal ultimate bearing capacities increased by 20–29%, and 25–34%, respectively. In the case of the bucket with increased support, when other parameters remained unchanged and the displacement at the top center of the bucket had increased, the rotation point will move to the center of the bottom plane of the bucket. Under the same central displacement of the bucket top, the foundation rotation point moved vertically downward relative to the bucket as the length of supports became longer. Under the sinusoidal horizontal cyclic load with an amplitude of 150 N, the traditional bucket foundation had a plastic failure, while the bucket with supports showed no plastic failure and little displacement.
... Many researchers have studied the bearing characteristics of bucket foundations on soft soil foundations by theoretical calculation [2][3][4][5], experimental research [6][7][8] and numerical simulation [9][10][11][12]. These researchers consider the influence of foundation shape, foundation burial depth, soil strength heterogeneity and other factors on the bearing performance of bucket foundations. ...
Multi-barreled composite foundations are generally used in offshore oil platform structure. However, there is still a lack of theoretical analyses and experimental research. This paper presents the results of a three-dimensional finite element analysis of a four-barreled suction pile foundation in heterogeneous clay foundation. The pile group effect and carrying capacity are numerically simulated. The effects of different pile embedment depths, pile spacings and non-uniformity coefficients of clay on the pile group effect are studied. Considering the changes in the foundation carrying capacity under vertical, horizontal and bending moment coupling loads, the foundation carrying capacity envelopes under horizontal and moment (H-M) and vertical, horizontal and moment (V-H-M) loading modes are drawn. The results show that pile spacing and embedment depth have great influence on the pile group effect. The bearing capacity envelope of foundations under V-H-M loading mode is greatly affected by vertical load V. This can provide a reference for the selection of pile spacing and embedded depth in practical engineering design. Furthermore, the stability of foundations can be evaluated according to the relative relationship between design load and failure envelope.
... Other scholars have further studied the stability of wind power foundations through indoor experiments combined with numerical simulations. For example, Ahn et al. [24] and Wang and Cheng [25] conduct numerical simulations and model tests to study the ultimate bearing capacity of the suction bucket foundation under vertical loads, horizontal loads and bending moments, and combinations of these loads. Zhu et al. [26] studied the bearing capacity, failure mechanisms, and load-displacement response of the suction bucket foundation under cyclic loads caused by wind, waves, and water currents. ...
In conjunction with the geological conditions of the East China Sea, the bearing performance of monopile and single-suction bucket foundations is compared and analyzed in shallow and deep-sea conditions under static horizontal loads. Furthermore, the statistical data of wind and wave from 2010 to 2020 in the East China Sea were tabulated into amplitude curves applied to the two foundations in the form of dynamic loads, and the bearing performances of the two foundations under dynamic loads were analyzed. The results show that the typical suction bucket foundation for a wind turbine currently designed in the shallow sea is destabilized under static horizontal loads, while the pile foundation is more stable; both foundations are stable in the deep-sea area. However, the suction bucket foundation displacement is less than the pile foundation. Under dynamic loading, the maximum displacement of monopile in the shallow sea was 127 mm. The maximum displacement of the suction bucket foundation was 434 mm, and the foundation was unstable. Both foundations are stable in deep-sea conditions, and the maximum displacement of the pile foundation is 1.4 times the maximum displacement of the suction bucket. Considering the difficulty construction in the deep sea, it is recommended to use suction bucket foundations.
... In case of the problems involving soil media, the widely employed basis to check the shear failure is the Mohr-Coulomb (MC) yield criterion. 2 On the other hand, for rock media, the generalized Hoek and Brown (GHB) yield criterion has been found to be the most acceptable. [3][4][5] Various plane strain and three-dimensional stability problems involving foundations, [6][7][8][9][10] anchors, 11,12 tunnels, [13][14][15] retaining walls, 16 trapdoors, 17 slopes, 18,19 suction caissons 20,21 have been analyzed on the basis of the MC yield criterion with the applications of both the LB and the UB FELA techniques. The axisymmetric problems can either be solved by using a three-dimensional approach involving three-dimensional elements or by performing a two-dimensional analysis with the usage of planar elements. ...
... In a similar fashion, Equations (20) and (25) can also be cast in matrix form as Equation (26). Finally, all these matrices can be joined together in terms of the following equation: ...
By using the lower bound finite elements limit analysis (LB-FELA) and the power cone programming (PCP), a methodology has been introduced to solve an axisymmetric stability problem with the usage of the generalized Hoek and Brown (GHB) yield criterion- applicable for rock mass. The formulation involves the application of the GHB yield criterion in its native form without any smoothing and it does not require any assumption associated with the circumferential stress (σθ). The efficacy of the proposed formulation in a rock mass has been demonstrated by determining (i) the bearing capacity of a circular footing, (ii) the stability numbers for an unsupported vertical cylindrical excavation, and (iii) the vertical uplift capacity of a circular horizontal anchor. The obtained solutions have been compared with that reported in literature. Failure patterns for each problem have also been explored. For the anchor problem, for no solution is reported with the usage of the GHB criterion, the influences of different material yield parameters (GSI, mi, and σci), unit weight of rock mass (γ), and the embedment ratio (H/B) of the anchor on the uplift capacity have been comprehensively examined.
... Applied Ocean Research 118 (2022) 103007 monopiles for offshore wind turbines is typically between 4 m and 8 m, with the length-to-diameter aspect ratio L/D ranging from 4 to 8 (Lombardi et al., 2013;Tseng et al., 2017). The diameter of caissons typically falls within the range of 3 m− 8 m, with L/D ranging from 0.5 to 6 (Randolph et al., 2011;Wang and Cheng, 2016). In this study, the diameter of the monopile and the caisson were maintained constant (D = 5 m), and the skirt wall thickness was taken as t = 50 mm. ...
Local scour may induce bearing capacity loss of the foundation significantly by removing soil around the foundation and it has become one of the pivotal factors causing the failure of structures in offshore engineering. Therefore, it is indispensable to investigate the effect of local scour on bearing capacity behaviour of foundations. This paper focuses on the effects of dimensions of local scour hole on both ultimate bearing capacities and failure envelopes of the monopile and the caisson in undrained soil with different soil strength heterogeneity ratios using three-dimensional finite element method. The results show that the scour depth has a more significant effect on the ultimate bearing capacity than the scour hole angle. Meanwhile, the scour depth has a more significant effect on the lateral bearing capacity (i.e., horizontal bearing capacity and moment) than on the vertical bearing capacity. For given dimensions of local scour hole, the effect of local scour on the bearing capacity decreases as soil strength heterogeneity ratio increases. Moreover, local scour affects not only the size of the failure envelopes of the monopile and the caisson, but also their shape. Based on the above findings, a procedure of designing the monopile and the caisson to consider local scour effect is proposed, which could be helpful to the design of the foundations in practical engineering.
... So far, most researches have focused on analyzing the responses of suction bucket foundation under monotonic and cyclic loads such as wind, wave and current. Numerical simulations or model tests were performed to study the ultimate bearing capacity of suction bucket foundation under vertical loads, horizontal loads, bending moment loads and the combination of these loads (Maniar (2004), Sukumaran et al., 1999;Cao et al., 2003;Monajemi and Razak, 2009;Li et al., 2014;Ahn et al., 2014;Wang and Cheng, 2016;Jin et al., 2019;Faizi et al., 2019). The bearing capacity, failure mechanism and load-displacement responses of suction bucket foundation under cyclic loads induced by wind, wave and current were also investigated by some researchers (Chen and Randolph, 2007;Cheng et al., 2016;Zhu et al., 2017;Jin and Liang, 2021;Gelagoti et al., 2018;Guo et al., 2017;Zhang et al., 2019;Yin et al., 2020). ...
Suction buckets are widely used as foundations for offshore wind turbines because of its many advantages such as simple structure, convenient installation, low construction cost and reusable. It is very essential to perform the seismic response analysis of suction bucket foundations for the design of offshore wind turbines. However, the related research is still relatively rare. In this research, three-dimensional finite element analysis is performed to predict seismic responses of suction buckets for offshore wind turbines in clays by using a simplified kinematic hardening constitutive model available in the Abaqus library. The seismic bearing mechanism of bucket foundation in clays is investigated, and various factors affecting seismic responses of suction bucket are analyzed, including the soil strength, seismic intensity and frequency, and bucket geometry. The research results can provide a reference for the seismic design of suction bucket foundations for offshore wind turbines.
