Seismic activity often triggers liquefaction in sandy soils, which coupled with initial vertical tensile loads, poses a significant threat to the stability of suction bucket foundations for floating wind turbines. However, there remains a notable dearth of studies on the dynamic response of these foundations under combined seismic and vertical tensile loads. Therefore, this study developed a numerical method for analyzing the dynamic response of suction bucket foundations in sandy soils under such combined loading conditions. Through numerical simulations across various scenarios, this research investigates the influence of key factors such as seismic intensity, spectral characteristics, as well as the magnitude and direction of tensile loads on the seismic response of suction buckets. The results revealed that the strong earthquake may cause the suction bucket foundation of floating wind turbines to fail due to excessive vertical upward displacement. This can be attributed to that the accumulation of excess pore water pressure reduces the normal effective stress on the outer wall of bucket, and consequently decreases the frictional resistance of bucket-soil interface. Additionally, the above factors significantly influence both the vertical displacement of the suction bucket and the development of pore pressure in the surrounding soil. The findings can provide valuable insights for the seismic safety assessment of suction bucket foundations used in tension-leg floating wind turbines.

When analyzing the dynamics of wind turbines under the action of wind and ground motion, mass-point models cannot accurately predict the dynamic response of the structure. Additionally, the coupling effect between the pile foundation and the soil affects the vibration characteristics of the wind turbine. In this paper, the dynamic response of a DTU 10 MW wind turbine under the coupling effect of wind and an earthquake is numerically studied through the combined simulation of finite-element software ABAQUS 6.14-4 and OpenFAST v3.0.0. A multi-pile foundation is used as the foundation of the wind turbine structure, and the interaction between the soil and the structure is simulated by using p-y curves in the numerical model. Considering the coupling effect between the blade and the tower as well as the soil-structure coupling effect, this paper systematically investigates the vibration response of the blade-tower coupled structure under dynamic loads. The study shows that: (1) the blade vibration has a significant impact on the tower's vibration characteristics; (2) the ground motion has varying effects on blades in different positions and will increase the out-of-plane vibration of the blades; (3) the SSI effect has a substantial impact on the out-of-plane vibration of the blade, which may cause the blade to collide with the tower, thus resulting in the failure and damage of the wind turbine structure.

Soft clay is extensively distributed in the Yangtze River Delta of China. Many seismic events indicate that underground structures buried in soft soil may suffer severe damage from earthquakes. In this study, a series of bidirectional dynamic cyclic triaxial tests were conducted to investigate the dynamic behavior of soft clay, considering different confining pressures and consolidation stress ratios. A simplified equivalent seismic loading method based on the strain failure criterion was proposed. The obtained equivalent amplitude of soft clay calculating by the critical cyclic stress ratio is averagely 1.58 times that of the sand liquefaction method. Under equivalent seismic cyclic loading, the dynamic shear strain and excess pore pressure of soft clay increases with the increase of confining pressure. The relationship between the maximum excess pore pressure and the corresponding shear strain can be expressed by a hyperbolic function. Due to the weakening effect of seismic loading, the shear modulus decreases as the shear strain increases, with a sudden reduction of up to 45 %. The shear modulus and damping ratio increase with the increase of confining pressure and consolidation stress ratio. The research results may provide some valuable insights into the seismic design practices in soft clay areas.

Investment allocation for offshore wind turbines (OWT) as an important class of structures is typically carried out through supporting decision-making approaches utilizing some fragility functions. This study attempts to deliver fragility functions for OWTs on monopile foundations accounting for soil-structure interaction (SSI) effects. Simultaneous wind, wave, and earthquake loads were considered probabilistically by adjusting their occurrence hazard levels for predefined damage states in diverse performance levels. The designated damage states in this study are defined based on collapse probability and some targeted performance levels which could be very straightforward to distinguish. The damage state detection is based on rotation in the connection of the tower's transition part to the foundation, which perceptibly reveals the effects of SSI on fragility functions. The expected results comprise modified fragility functions accounting for SSI effects contributing to less median spectral acceleration, more evidently rotational demands, further dispersions, and a subsequent dominant increase in the probability of exceeding performance limit states. Considering operational performance level, the most applied design performance level for turbines as an important class of structures, not considering the SSI effects could noticeably underestimate the demands and lead to high-risk decisions.

The present research study aims to create accurate and comprehensive inventory mapping while investigating the geomorphological and geotechnical characteristics of the large, deep-seated, and damaging El Kherba landslide triggered by the August 7, 2020 (Mw 4.9) Mila earthquake. The methodology relies on the analysis of results obtained through detailed field investigations, satellite image interpretation, deep boreholes equipped with piezometers, laboratory tests, in situ tests, and numerical simulations. The resulting landslide inventory map reveals a significant earth slide with an active zone covering a surface area of 1.565 km2, extending approximately 2,166 km in length, with a width ranging from 40 m to 1.80 km, and a volume of 25,784,909 m3. Geomorphological field mapping results revealed a large and deep-seated morphological deformation related to: (i) the weak mechanical resistance and low stability slopes that the seismic strengths caused a reduction in the shear strength of the soil; (ii) Miocene clays, highly altered and potentially subject to shrinkage and swelling; (iii) a partial reactivation of a previously existing large landslide; (iv) human activity such as slope excavation and unplanned urbanization; and (v) topographical and lithological site effects. The results of geological and hydrogeological investigations indicated the presence of: (i) thin and thick weak-resistance interlayers of altered and plastic clays with weak resistance, which may constitute shear surfaces; (ii) a shallow aquifer that impacted the mechanical resistance characteristics. Laboratory tests revealed that the fine clay in the soil was highly weathered, with a low dry density and a high moisture content, along with a high saturation and plasticity, making it very sensitive to the presence of water. Undrained triaxial cyclic loading tests indicated a high potential for the generation of excess pore-water pressures in the material during seismic loading. The direct shear test showed that the disturbed soils had an average cohesion of 33.4 kPa/m2 and an internal friction angle of 18.21 degrees, indicating poor structural and shearing strength. The results of the oedometer test indicated that the soils are compressible to highly compressible, overconsolidated, and have the potential for swelling. According to the Manard pressuremeter test (MPT) and available empirical relationships, the landslide exhibited a deep-seated nature, with sliding surfaces located along weak geotechnical characteristics interlayers at a depth ranging between 10 and 40 m. The depths of failure obtained from the MPT were consistent with those determined by the empirical relationships available in the literature and numerical simulations. This comprehensive research provides valuable data on earthquake-induced landslide and can serve as a guide for the prevention and mitigation of landslide risks.

The safety and reliability of wind turbines subjected to multiple loads has recently attracted great attention. To investigate how soil-structure interaction (SSI) affects the seismic performance of operating wind turbines, a wind tunnel-shaking table test platform has been built which can realize applying wind load and seismic load simultaneously. A 1:100-scaled wind turbine model with two different kinds of foundations (soil-structure interactive foundation and rigid foundation) has been tested under four seismic excitations (El-Centro and Taft, input in two directions) when it keeps operating in wind excitations. Nacelle displacement with the soil-structure interactive foundation was significantly larger than that of the rigid foundation, reaching 3-5 times at a peak ground acceleration (PGA) of 0.8 g. The maximum nacelle displacement of the scaled model with soil-structure interactive foundation always occurs in the direction of incoming wind, unlike the rigid one occurring in the direction of seismic input direction. The rigid foundation model presents a strong whipping effect with an acceleration amplification factor of the tower top (APF = 3). In contrast, the model with soil-structure interactive foundation shows mild whipping effect due to smaller foundation stiffness (APF of the tower top = 1.5). The study demonstrates SSI could weaken dynamic responses, reducing bending moments but inducing excessive nacelle displacement, risking structural damage. This study underscores the importance of SSI in evaluating the safety and reliability of wind turbines subjected to the wind and seismic loads and provides experimental results for future designs.

Rubble mound breakwater is a coastal structure, which is constructed to provide tranquil conditions in and around the port areas. Generally, the rubble mound structures are subjected to vigilant waves throughout the year. After the earthquakes of Kobe (1995), Kocaeli (1999), Tohoku (2011) etc. it is observed that the breakwaters can collapse due to failure of foundation and by seismic activity. Hence, in order to assess this problem, the current investigation deals with the study of rubble mound breakwaters and it is behavior against the seismic forces using numerical analysis. A finite element software PLAXIS is used for the numerical simulations. For study, a prototype has been selected and numerical model developed is a conventional rubble mound breakwater. In countermeasure model, the sheet piles in the foundation soil on extreme side of mound were considered. The numerical analyses have been done for constant seismic loading and soil properties. The parameters like vertical settlement and horizontal displacement were determined at different nodes. The vertical settlement was observed to be predominant in the crest region and it was reduced by 38% in countermeasure model. The displacement contours were significantly seen in core and armor units. The horizontal displacement of mound was seen by lateral movement of outer layers and it was 23% lesser for sheet pile reinforced model.