Scour Conditions Research Articles

Study of the dynamic response of an offshore continuous beam bridge under nonlinear wave and scour

The study highlights the critical factors and findings regarding bridge damage susceptibility during typhoons and hurricanes, primarily due to extreme waves, scour, and storm surges. While existing research has extensively studied bridges' responses to either extreme waves or scour individually, their combined effects have not been sufficiently explored. Experiments were conducted on a scaled two-span bridge to examine its behavior under simultaneous wave and scour conditions. Results from these experiments indicate that as scour depth increases, there is a corresponding escalation in displacement of the bridge pier, acceleration of the bearing platform, and strain along the pile foundation. To further investigate these dynamics, fluid-structure interaction analysis was employed, revealing significant insights. Notably, the study found that wave height exerts a substantial influence on wave load. For instance, at a wave height of 6 m, the average peak horizontal wave load on bridge piers was 2.48 times higher than at 3 m wave height. Moreover, local scour was identified as a critical factor reducing the bearing capacity of pile foundations, thereby significantly impacting the bridge's dynamic response to nonlinear waves. Under identical wave conditions, varying scour depths (3 m, 6 m, 9 m, and 12 m) resulted in increases in peak lateral displacements at the pier top compared to non-scouring conditions. The study concludes by emphasizing the increasing risk posed to pile foundations with deeper scour depths, particularly under stronger wave conditions. Consequently, there is a crucial need to enhance the resilience of offshore bridges against these dual hazards through advanced design and protective measures.

Macro-element modelling for lateral response of monopiles with local scour hole via hyperbolic hardening relation

Monopile is a popular choice in the foundation supporting offshore wind turbines (OWTs), with local scour significantly impacting their lateral responses. Macro-element model, which encapsulates the response between the monopile and the surrounding seabed soils into a force-displacement relation, has been extensively developed to describe offshore foundations. However, such kind of models specifically targeting monopiles subjected to lateral loading in local scour remain underdeveloped. This work proposes a macro-element model with a succinct hyperbolic hardening relation for laterally loaded monopiles in local scour conditions, using the evolutionary polynomial regression (EPR) machine learning technique for easy and optimal design. First, the finite element model is verified and extended to generate force-displacement responses considering the monopile geometries, soil characteristics, and local scour geometries. These results are then utilised to determine the optimal hyperbolic hardening relation of the macro-element model. Next, the EPR technique is employed to determine the relationship between the hyperbolic hardening relation parameters and the influencing factors. Finally, the macro-element model is successfully evaluated by comparing with measurements from centrifuge tests and numerical solutions by finite element analysis, demonstrating its applicability in practical design and the ability to reproduce FEA results with a significant reduction in computational cost.

Rapid assessment of seismic performance of large monopile-supported offshore wind turbines under scour

This study focuses on investigating the seismic performance of a reference 15 MW offshore wind turbine (OWT) supported by a large-diameter monopile, under various scour conditions. Fully coupled nonlinear finite element models considering 3D soil continuum for seismic response analysis of monopile-supported OWTs are very complicated and computationally expensive. Therefore, it is important to have good insight on the dynamic behaviour of monopile-supported OWTs subjected to earthquake excitations before performing high-fidelity fully nonlinear 3D simulations, which will not generally be practical in cases considering various seismic loading and scouring scenarios. The purpose of this study is to provide a fast and efficient tool to understand the interaction between the seismic behaviour of emerging large-capacity OWTs when scour erosion affects the dynamic properties of the structure. The dynamic stiffness method (DSM) is applied for the free vibration analysis of the structure. Modal superposition is used to calculate the seismic responses of the OWT by using the exact mode shapes obtained from the dynamic stiffness formulations. The rotor-nacelle-assembly (RNA) is idealized as a lumped mass at the tower top. The tower and monopile are modelled as Timoshenko beam-columns under axial compressive loading. The soil-structure interaction (SSI) is modelled using the Winkler framework, whereby the soil contribution is assumed as elastic to take advantage of the modal superposition method. Two different approaches are considered for the soil stiffness; a constant profile, and a linearly-varying subgrade modulus along the embedded depth of the pile, and both are appraised in this paper. Firstly, natural frequencies obtained from dynamic stiffness formulations are validated using experimental data from literature for the case of controlled dynamic SSI experiments, and for operating OWTs. Additionally, the natural frequency provided by a technical document for the reference 15 MW OWT is compared to the result from the DSM, where a very good agreement is observed. The seismic response time-histories of the OWT model are obtained under different input earthquake conditions, and subsequently verified by comparison with the results of finite element simulations. The effects of different scour scenarios and foundation modelling approaches on the free vibration and seismic responses are subsequently investigated. A parametric analysis is also performed using different soil properties to observe the interaction between the soil stiffness, scour condition, and seismic response. Finally, the influence of the frequency content of seismic records on the dynamic response of the OWT, specifically the tower top acceleration, the mudline rotation, and the mudline stress, is investigated considering various scour scenarios. The specific numerical case study undertaken for a reference 15 MW OWT, which is supported by a large monopile in very dense sand, shows that the seismic responses are very limited and that the elastic soil behaviour assumption is reasonable. Additionally, considering the computational efficiency, the proposed combination of DSM and modal superposition can be used for rapid seismic performance assessment of large diameter monopile-supported OWTs at the preliminary design stage to gain insight to the global dynamic response of the whole vibrating system.

Seismic performance of skewed bridges with uniform and non-uniform scour

Seismic safety of highway bridges is one of the critical issues for the functionality of transportation lifelines after severe earthquakes. Skewed highway bridges are found to be more vulnerable due to the irregular distribution of seismic demands on the bridge components. Moreover, scour induced loss of soil material and hence reduction in lateral support around the foundation piles can amplify the seismic effects on the structural components of water crossing bridges. A numerical study was conducted to investigate the seismic performance of skewed and straight highway bridges with varying scour depths and two different scouring types around the bridge piles. Analytical models of straight (0°) and 45° skewed bridges were created using the OpenSees program and a series of nonlinear response history analysis was carried out under the effect of recorded strong ground motions. In the first scouring type which was called as Case-1, scour depth was assumed the same around all piles and varied uniformly. In Case 2, two different non-uniform scouring types with linearly varying scour depth around the piles were investigated. The uncertainty in the earthquake ground motion excitation direction of the two horizontal components was also studied by considering the variable incidence angle of ground motion pairs. The maximum seismic demands of the members at different ground motion incidence angles were evaluated and compared to the demands obtained for the critical ground motion incidence angles suggested by Caltrans. Superstructure displacement, curvature demands of bridge column and shear force demands of pile elements are the seismic demand parameters examined within the scope of the study and were compared for each scour condition for both straight (0°) and 45° skewed bridge.

A crashworthy device for bridge protection under vessel impact and scour

ABSTRACT For Bridges spanning navigable waterways, scour can amplify damage in the event of a vessel impact. This work investigates the effectiveness of a designed steel crashworthy device in reducing damage to a bridge already affected by scour when subjected to a vessel impact. The findings reveal that the crashworthy device can diminish the peak impact force compared to the bridge system without a steel fender under the same scour conditions. Moreover, the crashworthy device effectively dampens the dynamic response of the bridge during a vessel impact under the same scour conditions. However, with increased scour depth, the impact displacement increases even if a steel fender is used, which may still affect the normal service of the bridge system after collision at a deeper scour depth. Consequently, it is recommended to implement maintenance measures aimed at strengthening and enhancing the horizontal load-carrying capacity of the scoured pile foundation in such cases.

Effect of scour remediation by solidified soil on lateral response of monopile supporting offshore wind turbines using numerical model

Offshore wind turbines supported by monopiles are inevitably influenced by scour, which will weaken the support provided by soils around and reduce the lateral capacity of the foundations, potentially leading to structure failures. In response, solidified soil is recognized as a promising solution for scour remediation, not only effectively filling the scour holes but also increasing the overall bearing capacity of the monopile. Nevertheless, the mechanism for scour remediation of solidified soil to increase the bearing capacity of the monopile is still unclear. Therefore, this paper mainly investigates the impact of solidified soil on the lateral bearing capacity of monopiles under various scour conditions and compares the effectiveness of different scour remediation methods (i.e., inverted conical remediation to half or all of scour hole and cylindrical remediation to half or all of scour hole). Firstly, the effect of solidified soil on lateral responses of monopile was investigated numerically. The overall load-displacement behavior, profile of bending moment and deflection versus depth of monopile under different scour stages and scour remediation conditions have been fully studied, in addition to the displacement field and failure mode of soil around monopile. It was found that solidified soil can greatly improve the lateral capacity and initial stiffness of monopile, and the cylindrical remediation to all of scour hole scenario showing the greatest improvement. After remediated by solidified soil, the resistance of soil around the monopile is greatly improved, and the rotation center position of monopile is moved up. Furthermore, a series of supplementary sensitivity analyses were conducted to study the effects of remediation parameters (i.e., elastic modulus and strength of solidified soil) and original soil parameter on lateral capacity of monopile.

Numerical Analysis of Flow Structure Evolution during Scour Hole Development: A Case Study of a Pile-Supported Pier with Partially Buried Pile Cap

This study numerically investigates a pile-supported pier, which comprises a column with a partially buried pile cap and a group of piles, recognizing that partially buried pile caps lead to the highest scour depth. Most research has focused on equilibrium scour conditions in laboratory settings, overlooking the detailed dynamics of horseshoe vortices around pile groups. This study aims to clarify the flow structure and vortex dynamics at a pile-supported pier during local scour hole development stages using an in-house developed numerical model. The model’s accuracy is validated against flat-channel and compound pier reference cases. For the pile-supported pier, fixed bed geometry was used in flow simulations at selected scouring stages. Results show significant changes in flow structure and vortex formation with scour hole time development, particularly as the bed surface moves away from the pile cap. The study reveals variations in vortex size, number, and positioning, alongside turbulent kinetic energy and Reynolds shear stress distributions over time. High positive Reynolds shear stress near the bed during intermediate scouring stages highlights the complex interactions within the flow field. This research provides the first detailed visualization of flow structure evolution within a scour hole at a pile-supported pier.

ArchIMEDES: Computer Vision Tracking of the Inherent Changes to Structural Stability of Masonry Arch Bridges Resulting from Increased Bed Scour.

Scour-induced failure of masonry arch bridges is a common cause of bridge collapse, especially during extreme flood events. Over recent years there has been a significant increase in the numbers of documented scour induced failures of this bridge stock across Europe and the USA. The extent of the scour can erode the supporting soil or sediment around the bridge piers or abutments, leading to a loss of support for the structure. As the foundation becomes unstable, it can result in settlement or tilting of the bridge, potentially causing structural damage, while the ongoing nature of scour can result in the progressive deterioration of the bridge’s ability to safely transfer load. Traditional hydraulic adjustments, such as streamlining abutments with wing walls and using cutwaters on piers, do not significantly reduce scour depth for masonry arch bridges. This paper presents initial findings of an investigation that links the changes of response in load carrying capacity to the easement of support at the bridge foundation due to scour. Scale experiments on the FlexiArchTM under loading with realistic scour conditions is contributing to the development of an algorithm based on the relationship between the structural response of the FlexiArchTM and prevailing scour conditions. The computer vision-based monitoring package ArchIMEDES, developed as part of the research, will use this algorithm to predict current bridge scour conditions at any given time. This will allow for potential scour development to be identified and investigated before the bridge collapses, ensuring the security and safety of these vital pieces of infrastructure.

Characteristics and Mechanism of Downflow in Front of a Cylindrical Pier with Clear-Water Local Scour

Local scour often causes pier instability; however, the characteristics and mechanism of downflow, representing one of the crucial flow structures, are still unclear. In this paper, the interaction between the downflow and the horseshoe vortex system and the role of the downflow under clear-water local scour conditions are discussed, based on the stress distribution obtained via experiments and simulations. In the present experiment, more accurate data are measured by installing suitable sensors on 3D-printed models that reproduce the scour hole conditions at various times. The obtained results reveal that the downflow exhibits a strong interaction with the horseshoe vortex system. From the perspective of flow structures, the flow structures collide and rub against each other, which weakens the effect of the downflow. From the perspective of energy transfer, the horseshoe vortex system absorbs the energy carried by the downflow to develop and reduce the energy introduced into the sediment. In addition, shear stress is a crucial factor in maintaining a high tangent slope. When the shear stress is down to a minimum and is stable, the tangent slope rises with the growth of the pressure stress, which means that the downflow is able to promote scour depth development.

Seismic fragility analysis of simply supported bridges considering uncertainty in scour condition

Bridges are vital infrastructures but face compounding risks from scouring and seismic events. Although recent studies have explored these individual and overlapping hazards, they often utilize deterministic approaches and focus on specific bridge types in limited geographical areas. This study addresses these gaps by introducing a probabilistic framework for assessing the seismic performance of multi-span reinforced concrete (RC) highway bridges in the presence of scour-related uncertainties. A time-dependent scour model, informed by a Bayesian approach and literature-based uncertainties, is integrated into the framework. Probabilistic Seismic Hazard Analysis (PSHA) and record selection strategies are employed to define the seismic demand probabilistically. Monte Carlo simulation (MCS) is utilized to propagate combined uncertainties during the analysis, considering different scour scenarios defined according to the discharge peak condition of the flood event at the specific location of the bridge. In the last step of the probabilistic framework, fragility analyses are conducted on individual components and the entire system by means of nonlinear dynamic models and multiple stripe analysis (MSA). An actual five-span bridge with simply supported prestressed concrete girders, located in Chile, is used as application example of the proposed approach, considering measured hydrological data and seismic hazard of the real location of the bridge. The study identifies distinct vulnerabilities across various bridge components under scour conditions. Elastomeric bearings are particularly susceptible in scenarios characterized by low scour depths (low discharge peak condition). Conversely, abutments display heightened vulnerabilities as scour depth increases (medium discharge peak condition). Piles also exhibit notable vulnerability, escalating in scenarios with great scour depth (medium discharge peak condition). Notably, piles tend to be more susceptible than columns to scour effects, especially in bents featuring shorter columns. These disparities in vulnerability are influenced by the bridge design philosophy, as well as the synergistic effects of seismic forces and varying scour depths. System fragility curves further elucidate that the likelihood of exceeding specific damage thresholds varies according to different scour scenarios, with the deeper scour depth scenario, displaying the higher vulnerabilities.

A Numerical Model for the Scour Effect on the Bearing Capacity of an Offshore Wind Turbine with a Five-Bucket Jacket Foundation

As offshore wind farms move into deeper waters and the capacity of offshore wind turbines (OWTs) increases, a new type of OWT foundation needs to be developed. In this study, a new type of five-bucket jacket foundation (FBJF) was proposed based on the broad application of a multi-bucket jacket foundation (MBJF) in offshore wind farms. The soil around the OWT foundation is subject to scour due to the complex marine environment. To investigate the effects of scouring on the FBJF, a series of local-scour simplified finite-element models of the FBJF were established using ABAQUS, and the effects of scouring depth and the extent on the bearing capacity of the FBJF with the monotonic load were analyzed. Then, the failure envelopes of the FBJF under combined loading were obtained using the fixed-displacement ratio method, and the effects of various scour conditions on the failure envelopes were compared. The results indicate that the failure envelope profile contracts inward, and the bearing capacity decreases with the increasing scouring depth and extent. Furthermore, the failure envelopes of the FBJF under different vertical loads were calculated, and the FV-FH-FM failure envelopes of the FBJF were obtained through interpolation. Finally, the effects of different scour conditions on the FV-FH-FM failure envelopes of the FBJF were analyzed. The results show that the FV-FH-FM failure envelopes of the FBJF have similar profiles and follow the same trend under different scour conditions.

Impact behavior of a strengthened bridge substructure under scour and vessel collision

When subjected to a vessel collision in the presence of scour induced by wave-current or flood, a bridge can sustain more severe damage compared to the pristine bridge undergoing the same impact. Scouring diminishes the ultimate capacity of pile foundations and can result in local damage to piers and pile foundations post-collision. This study aimed to mitigate impact damage on a scoured steel reinforced concrete (RC) bridge by employing a concrete-filled steel tubular pier and increasing the pile foundation section area. Pendulum impact tests were conducted on four concrete-filled steel-tubular pier-pile foundation systems to study their impact behaviors with scour depth effects. Experimental results show that while the displacement at the top of the pier increases with scour depth, there is no observed local damage to the impacted pier, even at deep scour depths. Subsequently, an FE model of the steel RC bridge was developed to assess the local dynamic behavior and damage based on the validated model. The impact performance of the scoured bridge, reinforced with a concrete-filled steel tubular pier and an increased pile section area, was then evaluated. Compared to the pristine bridge, the pile foundation with scour is prone to yield under the same impact condition, especially at deep scour depths. The increased section area method significantly enhances impact performance and reduces potential local damage to pile foundations, even under deep scour conditions. Additionally, a concrete-filled steel tubular pier markedly improves impact behavior compared to a conventional RC bridge pier. These findings underscore the efficacy of structural enhancements in bolstering the resilience of bridges against vessel collisions in scour-prone environments.

The universal two-fifths law of pier scour

Understanding scour at bridge piers is crucial for safeguarding public safety, ensuring infrastructure resilience, and planning effective maintenance. Despite over six decades of extensive studies aiming to develop predictive formulas for the equilibrium scour depth at bridge piers, more than 20 000 highway bridges in the United States have been spotted “scour critical.” The traditional reliance on existing empirical formulas has posed a severe challenge for researchers, hindering to achieve a unified relation for the equilibrium scour depth from a fundamental scientific tenet. This perspective article presents a breakthrough—a universal law governing the equilibrium scour depth at a circular pier embedded in a sediment bed, specifically in clear-water scour condition. Derived from a phenomenological model, the universal law reveals that the equilibrium scour depth to pier diameter ratio obeys a consistent two-fifths scaling law with the introduction of a newly coined pier-scour number. This number accounts for all the key parameters involved in a local scour phenomenon, including the approach mean flow velocity, threshold shear velocity for sediment grain motion, approach flow depth, pier diameter, and sediment grain size. Importantly, the scaling law contains an additional term involving the drag coefficient raised to the power of 2/5, addressing the impact of the pier shape on the equilibrium scour depth. The derived universal law undergoes the validation through an extensive dataset of experimental measurements on circular pier scour.

Seismic resilience assessment of extended pile shaft supported coastal bridges considering scour and uniform corrosion effects

The resilience-informed assessment for coastal highway bridges exposed to multiple hazards plays a crucial role in the decision-making process for their operation, maintenance, and management during the bridge’s long-term service period. This study performs a seismic resilience assessment for a coastal reinforced concrete (RC) bridge under the combined effects of scour and uniform corrosion. Toward this goal, an extended pile shaft supported coastal RC bridge is taken as the benchmark and fifteen scenarios are generated to cover three regular scour conditions and five different corrosion levels. To inform the bridge management, the probabilistic distribution of the bridge service time corresponding to different corrosion levels is developed. Subsequently, the finite element model (FEM) for each scenario of the benchmark coastal highway RC bridge is developed, involving the soil-pile interaction and considering the uncertainty of structural and geotechnical parameters, as well as earthquake ground motions. The failure mode of the corroded extended pile shaft is identified as a flexural failure by comparing their flexural and shear capacities. Finally, a resilience loss ratio is proposed in this study for the first time to quantify the impacts of corrosion level and scour depth changes on seismic resilience across different ground motion intensities. Results indicate that both the seismic fragility and resilience decrease as the corrosion intensifies over time. Specifically, at a given intensity measure (IM) level, the resilience loss ratio increases as the corrosion level intensifies. For the studied benchmark bridge, the scour significantly increases the structural fundamental period, consequently reducing the curvature demand on the pile shaft. As a result, the scour generally decreases the failure probability and the earthquake-induced functionality loss for the extended pile shaft. As scour depth increases, the resilience loss of the bridge at a given corrosion level decreases.

Numerical investigation on lateral monotonic and cyclic responses of scoured rigid monopile based on an integrated bounding surface model

Offshore wind turbines (OWTs) are affected by wind, wave, and current during their service life, which lead to the substructures undergoing combined effects of complex lateral loads and local scour. This phenomenon poses a significant challenge to the bearing capacity and cyclic responses of the widely used rigid monopiles for OWTs. This study develops three-dimensional numerical model to investigate the behavior of a rigid monopile subjected to lateral monotonic and cyclic loads, considering the stress history alteration induced by local scour. The hysteresis and plasticity accumulation of soils are captured by a bounding surface model. An accurate and concise semi-implicit stress integration scheme is creatively proposed to effectively incorporate this advanced constitutive model into the finite element (FE) software. The numerical model is verified by comparing FE results with centrifuge test results. Subsequently, the key factors such as cumulative deformation characteristics and bending moments distribution are investigated under different scour and cyclic loading conditions. The results indicate that with the facilitation of proposed semi-implicit scheme, the bounding surface model is capable of capturing the deformation pattern and cumulative deformation behavior of laterally loaded rigid monopile, and the cyclic responses of the monopile are significantly affected by the local scour.

Scoured failure wedge model for analysis of scoured pile-soil interaction in sand

Comprehensive assessment of scour effects is an important consideration in the design of pile foundations in water bodies because they can have a significant impact on the performance and bearing capacity of piles and the integrity of the supported structure. This study presents a scoured failure wedge (SFW) model to simulate the interaction between the laterally loaded pile and sand with local scouring. The developed model is incorporated into an efficient theoretical method to analyze the nonlinear behavior of laterally loaded piles under scour conditions accounting for the scour-hole dimensions and soil stress history. The developed SFW model is validated by comparing its predictions with experimental observations from relevant literature. Subsequently, the validated solutions are utilized to investigate the lateral performance characteristics of the pile under scour conditions. The findings reveal several important insights: (1) the impact of scour on soil properties is primarily confined to the shallow zone, approximately four times the scour depth (4 Hs) below the mudline after scouring; (2) the scour hole dimension has a more pronounced influence on the behavior of laterally loaded piles compared to the soil stress history; and (3) the pile response under lateral loading is positively related to the depth and width of the scour hole and negatively related to the slope angle of the scour hole.

Effects of local scouring on capacities of monopile-wheel composite foundations in sand under lateral loading

This paper focuses on an innovative foundation type of monopile-friction wheel composite foundations, which aim to enhance the loading performance of offshore wind turbines (OWTs) while mitigating the negative impact of local scouring. The study utilizes numerical simulations to investigate the morphology of local scouring under unidirectional flow. Furthermore, the finite element method is employed to quantify the lateral bearing behavior, considering different scouring parameters, loading point heights, and pre-torsional loads. On this basis, the load bearing ratio of each part of the composite foundation under different scour conditions is also obtained. The results reveal that the horizontal bearing characteristics are significantly influenced by different scour parameters, loading point heights and pre-torsional loads. The local scouring can reduce the bearing capacity by about 38%, with scouring depth having the greatest effect, followed by the scouring angle and extent respectively. Moreover, as the loading point height and pre-torsional load increase, the lateral bearing behavior of composite foundations decreases. Notably, the friction wheel contributes more than 40% to the overall bearing capacity, underscoring its importance. The results provide valuable insights into further understanding the bearing behavior of the composite foundation and its potential engineering applications.

Numerical Study of the Flow and Blockage Ratio of Cylindrical Pier Local Scour

A three-dimensional large eddy simulation model is used to simulate the turbulent flow dynamics around a circular pier in live-bed and clear-water scour conditions. The Navier–Stokes equations are transformed into a σ-coordinate system and solved using a second-order unstructured triangular finite-volume method. We simulate the bed evolution by solving the Exner-Polya equation assisted by a sand-slide model as a correction method. The bedload transport rate is based on the model of Engelund and Fredsœ. The model was validated for live-bed conditions in a wide channel and clear-water conditions in a narrow channel against the experimental data found in the literature. The in-house model NSMP3D can successfully produce both the live-bed and clear-water scouring throughout a stable long-term simulation. The flow model was used to study the effects of the blockage ratio in the flow near the pier in clear-water conditions, particularly the contraction effect at the zone where the scour hole starts to form. The scour depth in the clear water simulations is generally deeper than the live-bed simulations. In clear-water, the results show that the present model is able to qualitatively and quantitatively capture the hydrodynamic and morphodynamic processes near the bed. In comparison to the wide channel situation, the simulations indicate that the scour rate is faster in the narrow channel case.

Seismic response and liquefaction characteristics of wide and shallow multi-bucket jacket foundation under scour conditions

Scour has a significant effect on the seismic response of offshore structures. Compared to monopiles, MBJFs are shallow foundations and scouring has a more detrimental effect on their earthquake performance. However, the combined impacts of scour and earthquake on the structural response and liquefaction characteristics of the MBJFs have not been completely investigated. Based on the secondary development of the ABAQUS program, this paper proposes a method for calculating the seismic response and liquefaction of MBJF under local scour conditions. The seismic response and liquefaction characteristics of MBJF-supported OWTs in silty soil are evaluated under different scour depths, scour ranges, earthquake motions, soil conditions, and structural damping. In comparison to the unscoured condition, the results show that the maximum horizontal displacement, lateral acceleration, and bending moment of MBJF-supported OWTs increase by 30%, 97%, and 58%, respectively. Liquefaction is generated mostly in the soil outside the bucket rather than inside. An increase in soil density can improve the lateral acceleration of the structure and reduce the proportion of liquefaction in the soil. The maximum reduction in liquefaction can be 70.2% for an increase of 23% in soil densities. Disregarding structural damping will overestimate the structural response and the proportion of soil liquefaction. The findings may shed light on the seismic response and liquefaction characteristics of MBJF-supported OWTs located in complex offshore scour environments.

Effect of scour erosion and riprap protection on horizontal bearing capacity and reliability of monopiles using FEM-BPNN-RSM coupled method

Scour erosion around monopiles of offshore wind turbines (OWTs) can significantly reduce their horizontal bearing capacity and reliability. To combat scouring, riprap protection has been identified as a simple and effective method. This study aims to analyze the impact of different scour depths and riprap protection on the horizontal bearing capacity and reliability of monopile-supported OWTs, considering the interaction between the structure and the soil. In this research, we establish three-dimensional finite element models and propose a novel coupled analysis method, integrating the finite element method (FEM), back-propagation neural network (BPNN), and response surface method (RSM), to assess the bearing capacity reliability under various scour and protection conditions. This analysis incorporates extreme value data from 30 years of marine environmental conditions and employes an 8MW wind turbine as a case study. By utilizing the established response surface, we determine the failure probability and reliability index. The results demonstrate that the rotational center of the monopile shifts either downward or upward with increased scour depth or implementation of riprap protection. Furthermore, the findings reveal that riprap protection not only effectively mitigates the negative impact of scour on the bearing capacity of monopiles but also enhances their bearing capacity and reliability directly.