Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Numerical Analysis of Combined Bearing Capacities of Deep Tripod-bucket Foundations
Zhihao Sun, Qilin Yin, Zhiming Yuan, Jinjin Zhai
School of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology.
Zhenjiang, Jiangsu, China

ABSTRACTIn this paper, a deep tripod-bucket foundation with a heightdiameter ratio of 2:1 is proposed. The three-dimensional finite
element model considering the interaction between the tripodbucket foundation and soil is established in ABAQUS. The
ultimate bearing capacities Hult, Vult and Mult of foundation inhomogeneous clay seabed under pure horizontal load (H),vertical load (V) and moment load (M) are calculated.
Furthermore, the loading performance of the foundation under
combined load conditions was studied with fixed displacement
ratio method. Considering the tripod-bucket foundation can
withstand upward and downward loads, the combined bearing
capacities under vertical upward (V+) and vertical downward (V-)
load conditions are involved in this study. Results show that Hand M in V+-H and V+-M load space decrease gradually with theincrease of V+. In V--H load space, H increases with the increaseof V-, then keeps constant, and then gradually decreases. In V--M
load space, M increases with the increase of V-, then decreases
gradually. In V-H-M load space, the H-M envelope isunsymmetrical about M axis. Under different V levels the shapeand range of each H-M envelope are different. Finally, thedimensionless standard envelope of the deep tripod-bucket
foundation is analyzed, and the failure mode of soil around themonopile is studied.
KEY WORDS: offshore wind turbine; deep tripod-bucket
foundation; combined bearing capacity; failure envelope; failuremode
INTRODUCTION
As a towering structure, the offshore wind turbine (OWT) needs
to bear huge horizontal loads (H) and moment loads (M) as wellas vertical loads (V) due to the effect of wind, wave and current,Corresponding author

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leading to vertical displacements (w), horizontal displacements(u) and rotations (θ) of the foundation. This loading mode iscalled the combined loading mode (Salencon and Pecker, 1995).
Under combined loading conditions, the ultimate bearing
capacity of bucket foundation cannot be calculated accuratelyby the classical bearing capacity calculation formula, so
numerical modeling is generally adopted for analysis andcalculation (R Liu et al., 2014).
At present, there are some research results on the bearing
capacity of bucket foundation under combined loading condition.
Deng et al. (2011) studied the relationship between the size ofthe bucket foundation and its bearing capacity and analyzed theeffects of soil parameters on the vertical ultimate bearing
capacity of the bucket foundation. M Liu et al. (2015) studied
the bearing characteristics of bucket foundations under verticalloads with different length-diameter ratios. And the failuremodes of wide and shallow bucket foundation under verticalloads are analyzed. M Liu et al. (2014) studied the bearing
characteristics of wide and shallow bucket foundations ofoffshore wind turbines in silt. A new simplified calculationmethod for vertical bearing capacity and overturning stability
was proposed. R Liu et al. (2014) established the numericalmodel of a wide and shallow bucket foundation under combined
loads on undrained saturated soft clay foundation. The failureenvelopes of foundation were obtained and compared with thetraditional bucket foundation. R Liu et al. (2016) also studied
the failure envelopes of the single bucket foundation under the
combined loading condition, and model tests were performed toverify the numerical results. Ding et al. (2013) studied bearing
capacity of large-scale bucket foundation under the combined
loading conditions, compared the ultimate bearing capacities
and failure modes of two typical types of large-scale bucket
foundation. However, there are very few related studies on thecombined bearing capacity of tripod bucket foundation. He et al.
(2021) calculated the bearing performance of the shallow tripodbucket foundation with a height to diameter ratio of 1:2 in the