It is crucial to simulate the seismic behavior of offshore wind turbines, especially when dealing with foundations on non-cohesive soil. There is a risk of liquefaction occurring, which highlights the need to obtain values of excess pore water pressure. In this study, we created a three-dimensional model of a caisson foundation for an offshore wind turbine on loose sandy soil from the Syrian coast. The Mohr-Coulomb constitutive plasticity model was used to analyze two scenarios. The first scenario involved applying wind and earthquake loads, while the second scenario included marine currents and wave loads in addition to the wind and earthquake loads. We used Coupled acoustic-structural medium analysis after confirming its effectiveness on the soil through comparison with simulation results of the FLAC3D program from a previous study. The numerical modeling results indicated that it is possible to use Coupled acoustic-structural analysis in soil and water modeling. The study monitored the values of excess pore water pressure and found that liquefaction occurred in the soil due to the earthquake. The analysis also highlighted the importance of considering wave and marine currents loads in analyzing these structures. While these factors had a slight impact on excess pore pressure values, they significantly affected the directions and values of displacements.

Taking a caisson foundation engineering of a railway across-river bridge as the case, the technical characteristics and key challenges of over-deep inclined caisson were described firstly. Subsequently, the main controlling factors of the uneven settlement were analyzed. In view of the difficulty in obtaining the parameters of disturbed grouting soil, as well as the large adjustment of subsequent construction loads, an uneven settlement method based on over-deep underwater lateral pressure test and high-pressure consolidation test was proposed. The proposed method was simulated by finite element method to analyze the variations of total settlement, differential settlement and inclined attitude of caisson foundation under different loading stages. The results showed that the difference in the thickness of the disturbed layer was the dominant factor of uneven settlement, finally controlling the inclination shape. Grouting reinforcement was conductive to improving the settlement of caisson foundation. The maximum total settlement, differential settlement and offset after reinforcement were reduced to 249.53 mm, 19.54 mm and 29.20 mm, respectively. The deformation mainly occurred in the loading stage before the platform construction, accounting for about 60 %. If it is considered to level the top surface, adjust the elevation and load center during the construction of platform, the incremental settlement, the north-south differential settlement and the offset of top surface corresponded to 94.26 mm, 10.31 mm and 17.52 mm, respectively. Finally, the reliability of above method was fully verified by comparing the measured data with calculated value. The results will provide certain ideas and methods for relevant engineering problems. (c) 2024 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BYNC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Cyclic loading features in many applications. Questions important for design include: Does the monotonic capacity increase or decrease following cyclic loading? How does foundation rotation, stiffness and damping evolve? This is investigated here for suction caissons in sand, looking to applications as foundations for offshore wind turbines where changing stiffness, capacity and accumulated rotation can be critical, and soil damping is being looked at more closely. The problem is investigated experimentally through a series of single gravity monopod caisson tests in saturated sand subjected to unidirectional or multidirectional cyclic loading with between 360,000 and 106 cycles applied in each test. Results from the unidirectional tests are consistent with previous experimental studies, whilst also demonstrating the expected changes in damping ratio during cyclic loading for a monopod caisson in sand. The multidirectional tests reveal more significant and potentially important findings, particularly on the very significant increases in unloading stiffness and damping ratio associated with load direction changes.

During service period, offshore wind turbines are subjected to both monotonic and cyclic loads, causing the rotation or translation of caisson foundations in the seabed. However, most of the existing studies focused on the performance of caisson foundations under monotonic static loading, and there are few studies about the effects of caisson-soil contact mode and soil strength reduction during installation in numerical simulations. This paper therefore systematically investigates the bending moment capacity and failure mechanism of caisson foundations under monotonic and cyclic loading in clay using finite element analyses. Three typical caisson-soil contact modes in different loading scenarios are considered, and the influence of soil strength condition, caisson aspect ratio on the bending moment capacity and failure mechanism of caisson foundations is explored. It is found that under monotonic loading, the bending moment capacity in the tensionless mode and the fully-bonded mode could be used as the lower and upper limit, respectively. Under cyclic loading, the fully-bonded mode always yields the highest moment capacity, while the frictionless mode and the tensionless mode produce the lowest in the case with small loading amplitude and the case with large loading amplitude, respectively. In addition, the behavior of cumulative angular displacement under combined load of wind and wave is also studied to provide insight for caisson foundation design.