With the advantages of low construction costs and rapid installation, suction caissons are widely used as foundations in offshore engineering. This paper investigates the behavior of suction caisson foundations located in sandy soil under horizontal cyclic loads. The upgraded simple anisotropic sand constitutive model with memory surface (SANISAND-MS model) is employed to accurately capture the sand's cyclic behavior. To calibrate the parameters of the upgraded SANISAND-MS model, a series of triaxial drained monotonic and cyclic tests was performed. The effects of load idealization and loading sequence on the cyclic behavior of sand are studied based on the element test results, and the effects of load idealization on the cyclic response of suction caissons are studied from a finite-element simulation perspective. The triaxial test results indicate that load idealization slightly affects strain accumulation in both loose and dense sand. Based on simulation results, it is found that the loading sequence of load packages with varying amplitudes has a minor effect on the rotation accumulation of the suction caisson. The current load idealization method used in the engineering design practice of suction caissons is acceptable under drained conditions.

Suction caisson, characterized by convenient installation and precise positioning, is becoming increasingly prevalent. Over prolonged service, a significant seepage field forms around the caisson, particularly in sandy seabed, altering the contact stress at the caisson-soil interface and causing change in the interface shear strength. Given these interface contact properties, a series of cyclic shear tests are performed, incorporating the effect of pore water pressure. Test results indicate that the interface shear strength depends on normal stress, while the interface friction angle is only minimally influenced. Drawing from the findings of the cyclic shear tests, a cyclic t-z model is established to simulate the seepage-influenced caisson-soil interface shear behavior, which is also validated at the soil unit scale through interface shear tests and at the suction caisson model scale by centrifuge tests. It is further employed to forecast the evolution of skirt wall friction for a cyclic uplifting suction caisson, showcasing the capability in capturing the foundation failure under high-amplitude cyclic loading.

This study examines the failure mechanisms of offshore caisson-type composite breakwaters (OCCBs) under seismic loading through 1g shaking table model tests, comparing cases with and without remediation measures against seabed soil liquefaction. For this purpose, several countermeasures are implemented, comprising wraparound geogrid inclusions within the rubble mound layer, stone columns and compacted improvement zones in the seabed soil, all aimed at enhancing the seismic resilience and stability of OCCBs. Six physical model tests are conducted to evaluate the effectiveness of the applied remediation measures in minimizing liquefactioninduced deformations of OCCBs, including settlement, lateral movement, and tilting. Experimental findings indicate that the caisson settlement is primarily caused by the lateral flow of the foundation soil and the rubble mound layer. The combined use of stone columns and wraparound geogrid reinforcements efficiently mitigates this lateral flow. Notably, remediating just 2.8 % of the liquefiable seabed soil with stone columns decreases OCCB settlement and tilting by 45.4 % and 31 %, respectively, compared to the non-remediated model. Additionally, incorporating wraparound geogrid reinforcements within the rubble mound layer results in even further reductions of settlement and tilting by 90.6 % and 91.3 %, respectively. This research offers valuable insights for developing effective countermeasures to mitigate seismic-induced damage to OCCBs seated on liquefiable seabed soils.

Past seismic events have shown that caisson quay walls are susceptible to severe damage during earthquakes, underscoring the importance of assessing their seismic behavior. However, very limited studies have been conducted on the soil-structure-water interaction of the caisson-ground system during earthquakes. This study will investigate the seismic response and failure mechanism of a caisson through a centrifuge shake-table test. Specifically, the seismic response results of the backfill, the caisson, and the subsoil are discussed; an acceleration integration method for identifying permanent displacement to estimate the backfill deformation is proposed; and a phase analysis of the seismic response of the caisson-ground system is conducted. It is found that the liquefaction of the backfill results in a substantial increase in the dynamic earth pressure behind the caisson. The failure mode of the caisson is lateral movement accompanied by slight tilting and continuous rocking vibrations. The proposed acceleration integration method can effectively estimate the deformation and lateral spreading of backfill. Phase analysis results reveal the relationship between the failure of the caisson-ground system and seismic action.

Earthquakes are a major factor affecting the stability of marine structures, and liquefaction occurs in saturated sandy soils, causing damage such as settlement, tilting, and collapse of structures. The 2017 Pohang earthquake was the first case of liquefaction in South Korea, resulting in damages at Yeongilman Port, including caisson settlement (approximately 10cm), hinterland settlement (10-20cm), and horizontal displacement (less than 15cm). In seismic response analysis, undrained conditions are typically assumed; however, this approach has limitations as it fails to account for additional displacements occurring after the dissipation of excess pore water pressure. To address this issue, an analysis considering drained conditions is necessary. Therefore, this study investigates the liquefaction-induced damage under drained conditions considering the dissipation of excess pore water pressure and explores methods to mitigate damage through ground improvement. As a result, the stability of the caisson breakwater was secured by improving the sandy ground beneath the caisson.

Open caissons are increasingly utilized for underground construction due to the increasing demand for aboveground structures, which employ the principle of submersion using the self-weight of the edge cutting face and the applied bearing pressure to mitigate the vertical soil reaction. This paper examines the bearing capacity factor of the edge cutting face in anisotropic clays, approximated using the finite element limit analysis (FELA) method and considering the average results between the upper and lower bounds. The influence of the adhesion factor at the interface of the cutting edge (alpha), the ratio between the depth of the internal embedment and the embedded width (H/B), the ratio between the radius and the embedded width (R/B), the anisotropic shear strength (re), and the cutting face angle ((1) is investigated. The results indicate a significant influence of the anisotropic shear strength on the adhesion factor at the interface of the cutting edge. An increase in re denotes a decrease in the undrained shear strength obtained from the triaxial compression test, resulting in an increase in the value of N. An increase in alpha influences (1, such that when (1 <90 degrees, the value of N remains constant when (1 = 90 degrees. In addition, a highly efficient hybrid model called DNN-PBT was established utilizing a deep neural network (DNN) and a population based training (PBT) approach, specifically for the purpose of accurately predicting the bearing capacity factor of circular open caissons positioned in undrained clay. Both computational and comparative outcomes demonstrate that the proposed DNN-PBT can precisely forecast the bearing capacity, achieving an R2 value higher than 0.999 and a mean squared error (MSE) <0.007. These findings highlight the accuracy and efficiency of the suggested approach. Furthermore, the sensitivity analysis results demonstrated that the anisotropic shear strength (re) is the most important input variable for estimating the bearing capacity factor of the edge cutting face.

Suction caissons have been used in floating offshore wind farms worldwide with new types of finned suction caissons emerging to resist torque-loading. The additional fins attached to the caisson are expected to improve the torque-bearing performance, but the mechanism is yet to be clarified. Therefore, a novel torsional centrifugal modelling test system is developed to investigate the interaction between finned caisson and soil. The system is composed of the interacting chamber, the loading module, the transmitting module, and the measuring module. It allows precise control of the suction caisson penetration and pure torsional loading, which is validated by two torsion tests on a traditional caisson and a finned caisson. The results show that the torque-bearing capacity of the finned caisson is about 9.7 times that of the traditional caisson. The existence of the fins changes the failure mode from the interfacial friction failure between the caisson and the soil to the global soil-soil shear failure. The development of pore water pressure in soil was significantly changed by fins during torsional loading. The sudden change in the pore water pressure and soil pressure on the rear side of the fins indicates that tension gaps can be produced. The test results indicate that the developed test system is capable of evaluating the torsional performance considering foundation-soil interaction effectively.

As an innovative foundation used in the offshore floating platform, the scaled suction caisson (SSC) has a greater advantage in the installation and service than the traditional suction caisson (TSC). To investigate the pull-out capacity of the SSC, the numerical simulations are carried out under static and cyclic loads. The study shows the inclined pull-out capacity of the SSC increases with increasing the loading angle., but firstly increases, then decreases with increasing the padeye depth. Compared with the TSC, the inclined pull-out capacity of the SSC increases by 20 similar to 40% when the loading angles. are in the range of 0 similar to 30 degrees, but its values increase by 100% when the loading angles exceed 60 degrees. Under the combined static and cyclic loads, the vertical cumulative displacement of the SSC decreases, but horizontal cumulative displacement increases. The total cumulative displacement of the SSC decreases by 13% compared with the TSC. It can be concluded that more soils can mobilized by the bio-scale surface to resist the pull-out loads. As a result, the SSC significantly improves inclined pull-out capacity and decreases the cumulative displacement.

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.

Suction caisson is a new offshore wind power foundation structure developed in recent years. Understanding its penetration characteristics is crucial to the successful application. A field test was conducted in the eastern waters of Rudong, Jiangsu Province, China, to investigate the penetration process of suction caisson. The test results demonstrate that suction caisson can penetrate smoothly to a predetermined elevation of seabed soil under the complex environmental loads, such as natural wind and wave currents. The inclination of the caisson is only 0.018 degrees degrees once the penetration process is complete. The pore water pressure at the outer skirt is primarily influenced by the tide level and drainage conditions of the contact soil layer during penetration, and the peak effective interface pressure at the skirt-soil interface decreases by about 46.7% due to negative pressure inside the skirt. Frictional fatigue effects are found at the skirt-soil interfaces. Meanwhile, the seepage reduction and squeezing induced resistance effects at the skirt-soil interface are the leading causes for the different distributions of effective interface pressure between the inner and outer skirts of the caisson. The findings of this study can guide the future penetration of suction caisson under challenging geological circumstances.