Wave-induced Liquefaction Research Articles

A numerical model for assessing the effect of low clay content on wave-induced seabed liquefaction

In the marine environment, the seabed contains a certain amount of clay. Experimental studies show that the liquefaction susceptibility of the sandy seabed increases as clay content (CC) rises to a certain threshold, beyond which further increases in CC reduce liquefaction susceptibility. However, numerical models that describe the effect of CC on seabed liquefaction are very limited. This study proposed a dynamic poro-elasto-plastic finite element method model for analyzing liquefaction in the sandy seabed with CC below the threshold. Based on a series of undrained triaxial compression tests on sand-clay mixtures from existing literature, a unified constitutive framework was demonstrated to be effective for describing the liquefaction behavior of sand with low CC using one set of model parameters. Existing wave flume model tests validated the effectiveness of the proposed seabed model in describing the effect of low CC on excess pore water pressure (EPWP). Numerical results confirmed that adding a small amount of clay to the seabed increased the soil contraction and thus its liquefaction susceptibility. Wave-induced liquefaction was limited to a certain depth of the seabed, and the liquefaction depth was significantly affected by the CC. Adding a low content of clay the sandy seabed significantly increased both horizontal and vertical displacements under wave action, potentially leading to the instability of the seabed. This study provides a new method for accurately assessing the wave-induced stability of marine structures built on the sandy seabed containing certain amounts of clay.

Wave-induced liquefaction analysis of mildly sloping sandy seabed

Marine structures are commonly situated near the mildly sloping sandy seabed characterized by the slope angles (α) not exceeding 10°. The seabed liquefaction can be triggered due to the generation of the excess pore water pressure (EPWP), posing a threat to the stability of marine structures. This study focuses on the analysis of wave-induced liquefaction in the mildly sloping (MS) sandy seabed. A dynamic poro-elasto-plastic seabed model is developed to simulate the behavior of the MS sandy seabed under wave loading. The results indicates that the loading cycle required to trigger the initial liquefaction decreased as the position moved from the toe towards the crest of the MS sandy seabed. The amplitude of shear stress increases with the loading cycle and tends to increase with growing α before liquefaction, resulting in a slower accumulation of EPWP with larger α. Both the horizontal and vertical displacements induced by wave action reach the maximum at the crest of the sloping seabed. Notably, the horizontal displacement is much greater than the vertical displacement in the seabed under wave action. The displacement of the MS sandy seabed depends on not only the shear stress amplitude developed in the soils but also the accumulation of EPWP required to trigger the liquefaction in the seabed.

Simulating liquefaction-induced resuspension flux in a sediment transport model

Wave-induced liquefaction is a geological hazard under the action of cyclic wave load on seabed. Liquefaction influences the suspended sediment concentration (SSC), which is essential for sediment dynamics and marine water quality. Till now, the identification of liquefaction state and the effect of liquefaction on SSC have not been sufficiently accounted for in the sediment model. In this study, we introduced a method for simulating the liquefaction-induced resuspension flux into an ocean model. We then simulated a storm north of the Yellow River Delta, China, and validated the results using observational data, including significant wave heights, water levels, excess pore water pressures, and SSCs. The liquefaction areas were mainly distributed in coastal zones with water depths less than 12 m, and the simulated maximum potential soil liquefaction depth was 1.39 m. The liquefaction-induced SSC was separated from the total SSC of both liquefaction- and shear-induced SSCs by the model, yielding a maximum liquefaction-induced SSC of 1.07 kg·m−3. The simulated maximum proportion of liquefaction-induced SSC was 26.2% in regions with water depths of 6–12 m, with a maximum significant wave height of 3.4 m along the 12 m depth contour. The erosion zone at water depths of 8–12 m was reproduced by the model. Within 52.5 h of the storm, the maximum erosion thickness along the 10 m depth contour was enhanced by 33.9%. The model is applicable in the prediction of liquefaction, and provides a new method to simulate the SSC and seabed erosion influenced by liquefaction. Model results show that liquefaction has significant effects on SSC and seabed erosion in the coastal area with depth of 6–12 m. The validity of this method is confined to certain conditions, including a fully saturated seabed exhibiting homogeneity and isotropic properties, small liquefaction depth, residual liquefaction dominating the development of pore pressures, no influence by structures, and the sediment composed of silt and mud that experiences frequent wave-induced liquefaction.

A Methodology for Susceptibility Assessment of Wave-Induced Seabed Liquefaction in Silt-Dominated Nearshore Environments

Wave-induced seabed liquefaction significantly jeopardizes the stability of marine structures and the safety of human life. Susceptibility assessment is key to enabling spatial predictions and establishing a solid foundation for effective risk analysis and management. However, the current research encounters various challenges, involving an incomplete evaluation system, poor applicability of methods, and insufficient databases. These issues collectively hinder the accuracy of susceptibility assessments, undermining their utility in engineering projects. To address these challenges, a susceptibility assessment method with the safety factor was developed as the key assessment parameter, allowing for a comprehensive susceptibility assessment across the silt-dominated nearshore environment using Empirical Bayesian Kriging (EBK). The safety factor is determined by combining the cyclic stress ratio (CSR) and the cyclic resistance ratio (CRR), which characterize wave loadings and sediment properties in the study area, respectively. This method was applied in the Chengdao region of the Yellow River Estuary, China, a typical silt-dominated nearshore environment where wave-induced liquefaction events have been reported as being responsible for multiple oil platform and pipeline accidents. By collecting the regional wave and seabed sediment data from cores spanning from 1998 to 2017, the safety factors were calculated, and a zonal map depicting the susceptibility assessment of wave-induced seabed liquefaction was created. This study can serve as a valuable reference for the construction and maintenance of marine engineering in liquefaction-prone areas.

Effect of particle composition and consolidation degree on the wave-induced liquefaction of soil beds

Effect of particle composition and consolidation degree on the wave-induced liquefaction of soil beds

Study on the release of microplastic particles with different particle sizes in sediments caused by wave-induced liquefaction

Every year, almost 1.15–2.41 million tons of plastic from terrestrial rivers undergo fragmentation under certain conditions and settle in the estuarine delta and shallow marine shelf areas, making this region a “sink” for land-based microplastics. Owing to its fast deposition rate, relatively soft sediment bed, and shallow water depth, the estuarine delta region is prone to liquefaction under high wind and wave conditions. This could potentially release deeply buried microplastic particles during the liquefaction process, posing further threats to marine ecology and human health. To investigate this phenomenon, laboratory experiments were conducted using a water tank to simulate wave-induced liquefaction of sediment beds. The results showed that under the influence of wave-induced liquefaction, 56.2 % of microplastic particles were released back into the sediment surface, with larger particles being released to a greater extent. Based on these experimental results, this study also analyzed and discussed the release rate and mechanisms of microplastic particles from sediment during wave-induced liquefaction, estimating that the maximum release rate of microplastic particles under the experimental conditions could reach 0.34 mm/min.

Neural network models for seabed stability: a deep learning approach to wave-induced pore pressure prediction

Wave cyclic loading in submarine sediments can lead to pore pressure accumulation, causing geohazards and compromising seabed stability. Accurate prediction of long-term wave-induced pore pressure is essential for disaster prevention. Although numerical simulations have contributed to understanding wave-induced pore pressure response, traditional methods lack the ability to simulate long-term and real oceanic conditions. This study proposes the use of recurrent neural network (RNN) models to predict wave-induced pore pressure based on in-situ monitoring data. Three RNN models (RNN, LSTM, and GRU) are compared, considering different seabed depths, and input parameters. The results demonstrate that all three RNN models can accurately predict wave-induced pore pressure data, with the GRU model exhibiting the highest accuracy (absolute error less than 2 kPa). Pore pressure at the previous time step and water depth are highly correlated with prediction, while wave height, wind speed, and wind direction show a secondary correlation. This study contributes to the development of wave-induced liquefaction early warning systems and offers insights for utilizing RNNs in geological time series analysis.

Fluid characteristics of wave-induced liquefied silty seabed and the resulting wave attenuation

Wave-induced liquefaction of silty seabed is a common submarine geological hazard that poses a significant risk to the safety of marine structures. The liquefied seabed exhibits fluid properties and fluctuates with the overlying wave. To investigate the interaction between waves and the liquefied seabed, a wave flume experiment was conducted to simulate the wave-induced liquefaction process. During the experiment, the variation in the fluctuation trajectory and viscosity coefficient of liquefied silt with the wave intensity and liquefaction process were measured. Additionally, the wave energy dissipation due to seabed liquefaction was analyzed. The results indicate that the viscosity coefficient of the liquefied seabed is closely related to the wave intensity and liquefaction process, with the viscosity coefficient of the liquefied seabed being larger in the liquefaction deposition stage than in the liquefaction development stage. Seabed liquefaction can lead to a considerable increase in wave energy dissipation, up to 15 times greater than when the seabed is stable. Furthermore, wave energy dissipation is greater for high waves than for low waves conditions. The primary factors causing wave energy dissipation are the viscosity friction inside the liquefied seabed and the suspended sediment in the upper water column.

Numerical investigation into wave-induced progressive liquefaction based on a two-layer viscous fluid system

Based on a two-layered viscous fluid theory, a numerical model to capture the progressive nature of wave-induced liquefaction has been developed. Unlike the existing models, this model can consider the cyclic shear stress associated with vibrating liquefied soil layers and its effect on sub-liquefied soils during the wave-induced liquefaction. The reliability of this model is validated by simulating wave flume tests, which show a promising prediction when compared to analytical solutions, particularly after the onset of liquefaction where an increased amplitude in the oscillatory pore water pressure can be observed. The numerical results show that the moving characteristics of liquefied soil are similar to those of a water particle in the presence of surface water waves with the horizontal velocity being much greater than the vertical velocity. Unlike the model without considering the liquefied soil-induced cyclic shear stress, the proposed model predicts a prompt increase in residual pore pressure associated with the onset of liquefaction at shallow soil layers, which may change the curvature of residual pore pressure versus time in sub-liquefied soils from concave downwards to concave upwards at a certain depth. This phenomenon is consistent with many of the existing experiments for wave-induced seabed response and becomes more pronounced as the kinematic viscous characteristics of liquefied soil become more apparent, i.e., with a larger kinematic viscosity coefficient. Correspondingly, the cyclic shear stress induced by the vibrations of liquefied soil can accelerate the downward advancement of the liquefaction front and result in a larger depth of liquefaction.

Effective stress analysis of residual wave-induced liquefaction around caisson-foundations: Bearing capacity degradation and an AI-based framework for predicting settlement

Excessive wave-induced pore pressure buildup around offshore foundations results in liquefaction, settlement and bearing capacity degradation, which may threaten the safety of Offshore Wind Turbines (OWTs). Despite the extensive research efforts on wave-induced seabed residual response in the recent years, there is still a lack of knowledge on mechanisms of wave-induced liquefaction and settlement around caisson foundations. Employing a code-based framework implemented in OpenSees, the cyclic response of wave-seabed-foundation (WSF) system is evaluated. Biot’s consolidation theory, linear wave theory and CycLiqCPSP constitutive soil model are integrated to evaluate the response of soil-foundation system accounting for the hydrodynamic pressure of wave imposed on the seabed surface considering the fully-coupled wave-seabed-foundation interaction (WSFI). Soil model parameters are calibrated against cyclic simple shear (CSS) tests and the numerical model is validated by a well-documented centrifuge experimental model. Various seabed characteristics, and a range of the geometrical properties of foundation with different OWT weights are put into practice for evaluating the geotechnical aspects of wave-induced liquefaction. Stress paths are provided to demonstrate quite different level of reduction in effective stresses and likelihood of liquefaction occurrence upon cyclic shear stresses application for different locations in the vicinity of the foundation area. The present study will also improve understanding of the interplay among the state variables on the wave-induced foundation settlement and bearing capacity degradation allow to feed the output data into development of simplified procedure for assessing the bearing capacity. Finally, results from over 250 analyses with different model configurations are used to provide an estimate of wave-induced caisson settlement with reasonable accuracy on the basis of artificial intelligence (AI) method known as Group Method of Data Handling (GMDH).

Wave-Induced Liquefaction and Stability of Suction Bucket Foundation in Drum Centrifuge

Wave-Induced Liquefaction and Stability of Suction Bucket Foundation in Drum Centrifuge

Coupled model to predict wave-induced liquefaction and morphological changes

Coupled model to predict wave-induced liquefaction and morphological changes

Wave-induced liquefaction in a silt and seashell mixture

This paper presents the results of an experimental investigation of wave-induced liquefaction in silt and seashell mixtures. Three kinds of sediments were used in the experiments: silt ( d 50 = 0.070 mm), coarse seashell ( d 50 = 2.87 mm), and fine seashell ( d 50 = 1.46 mm). With these sediments, three kinds of tests were carried out: silt-alone tests (the reference tests), tests with silt and coarse-seashell mixture, and tests with silt and fine-seashell mixture. The experiments showed that the influence of seashell content on wave-induced liquefaction is very significant. The susceptibility of silt to liquefaction is decreased with increasing seashell content. This is up to a certain point beyond which the mixture of silt and seashell becomes liquefaction resistant. For the seashells used in the experiments, this limiting value was found to be approximately S C ≈ 30 % , where S C is the shell content by weight. It is argued that this behavior is linked with the elastic modulus of the mixture. The present findings showed that the liquefaction criterion based on the initial mean normal effective stress in pure silt/sand can be extended to silt and seashell mixtures. A chart is proposed for an initial screening check of liquefaction potential. Furthermore, it is recommended that, if there is a liquefaction potential, standard assessment methodology may be implemented to check for liquefaction, provided that the elastic modulus and other properties of the soil and seashell mixture are incorporated into this assessment. • Wave-induced liquefaction in a silt and seashell mixture is experimentally investigated in a wave flume. • Influence of seashell content of the mixture on wave-induced liquefaction is found to be very significant. • The susceptibility of silt to liquefaction is decreased with increasing seashell content. • A chart is proposed for an initial screening check of liquefaction potential. • Mixing of the native soil with seashell with a sufficiently large seashell content offers an option as a counter measure in the prevention of backfill soils against liquefaction.

Characteristics and sedimentological significance of acoustic anomalies in silty seabed in the Yellow River subaqueous delta

Due to extraordinary natural geographical features, seabed topography, and sediment sources, wave-induced silt liquefaction is a common occurrence in the subaqueous delta of the Yellow River, China. When liquefaction occurs, the original sedimentary structure of silt is destroyed; after liquefaction, the sediment particles are rearranged and reconsolidated, resulting in distinct physical and mechanical differences between the liquefied material and the nearby adjacent strata that have not been subjected to liquefaction. Based on data from geotechnical testing (GT), scanning electron microscope (SEM) images, and sub-bottom profiling (SBP), the physical and acoustical characteristics of silt remoulded by wave-induced liquefaction (SRL) in the Yellow River subaqueous delta are determined. According to the GT results, liquefaction resulted in distinct decreases in the water content (2.6%), the void ratio (0.056), and the clay content (4.52%), as well as slight increases in the wet density (0.01 g/cm3), the dry density (0.05 g/cm3), and the grain size (d50) (0.015 mm). Per our SEM analyses, the SRL material is denser than the unremoulded silt, attributed to the rearrangement and reconsolidation of the silt particles. As can be determined from the high-resolution SBP data, that acoustically, the SRL is distinctly different from the adjacent intact strata. The smooth funnel-shaped features demarcate the extent of the region that has been subjected to a specific liquefaction and silt reconsolidation event. Due to the presence of a fault-like uplifted reflection event in the underlying strata, the SRL produces positive sound velocity anomalies on the order of 53–127 m/s. Analyses of the physical and acoustical characteristics of the SRL provides valuable insight into the engineering properties of seabed silt.

Experimental Study on the Influence of Pipeline Vibration on Silty Seabed Liquefaction

Free-spanning submarine pipelines are usually affected by vortex-induced vibration (VIV). Such vibration could influence the liquefaction of the supporting soil at both ends of the free spans and could have catastrophic consequences, including the failure of the local seabed and the displacing, sinking, or floating of pipelines. The influence of pipeline vibration on soil liquefaction has not been studied sufficiently. Therefore, we explored the influence of vortex-induced pipeline vibration on the excess pore pressure of silty soil around a pipeline using flume experiments. Our results showed that pipeline vibration could induce the buildup of excess pore-water pressure, even without wave loading. A fully liquefied zone was found close to the pipeline, where excess pore pressure reached the soil liquefaction criterion, which was surrounded by a partially liquefied zone. The extent of liquefaction depended on the vibration conditions and the weight and burial depth of the pipeline. The pipeline vibration amplitude increased after soil liquefaction. Unlike wave-induced liquefaction, pipeline-induced vibration liquefaction occurred at a critical value smaller than the initial mean normal effective stress. Considering the possibility of pipeline-vibration-induced seabed liquefaction, conventional approaches could underestimate the potential risks to pipeline stability and result in unsafe maintenance practices.

3-D numerical study of offshore tripod wind turbine pile foundation on wave-induced seabed response

Investigation analysis of wave-seabed-structure interaction (WSSI) is a pre-requisite in every marine engineering design and construction due to the huge failure of offshore structures every year, resulting in financial losses. In this study, an integrated 3-D numerical model is established to investigate the wave-induced oscillatory seabed response around the offshore substructure foundation of the tripod support pile. In the integrated numerical model, the Reynolds-Average Navier-Stokes (RANS) equations with k−ε turbulence closure model for the mean fluid flow is applied as the governed equation for the fluid computation, while the Biot consolidation equations are applied as the governing equation for the porous seabed substructure foundation model. The integrated numerical model is validated against physical experimental data from other previous works; to demonstrate that the present numerical model has the capability and capacity of simulating the WSSI around the offshore tripod pile structure foundation, which indicated good results. The results from the wave-induced liquefaction around the tripod support pile show that liquefaction depth at the offshore area and the lateral area of the upstream axillary pile leg tends to be larger than the two axillary pile legs at the lee area.

Characteristics of the Sediment Gravity Flow Triggered by Wave-Induced Liquefaction on a Sloping Silty Seabed: An Experimental Investigation

The sloping silty sediments in estuarine deltas are frequently affected by extreme storms, and they are prone to liquefaction instability. The unstable liquefied sediments of the slopes can subsequently form a sediment gravity flow (SGF), which can seriously endanger offshore engineering facilities. To better understand the characteristics and mechanism of wave-induced liquefied sediment gravity flow (WILSGF), a flume experiment was conducted to reproduce the formation, movement, and deposition processes of the WILSGF and analyze their controlling factors using natural silty sediment samples collected from the Yellow River Delta in China. The results show that the mass of the WILSGF comes from the sediment in the liquefied layer, and the movement of the WILSGF in these experiments was significantly affected by the wave orbital velocity and the relative outflow position. At the initial stage of the formation of the WILSGF, the phase and amplitude of the WILSGF were the same as those of waves, and the maximum velocity of the WILSGF reached 2.39 cm/s. The velocity of the WILSGF decreased continuously with the downward evolution of the liquefaction interface. When the liquefaction depth reached its maximum value, there was no WILSGF. We also found that the median particle size of the WILSGF was greater than that of the original seabed due to wave-induced seabed coarsening and the intrusion of ambient water. This study has guiding significance for in-depth understanding and prediction of the geological hazards caused by WILSGF.

Numerical analysis of the seabed liquefaction around a fixed gravity-based structure (GBS) of an offshore platform and protection

The fixed gravity-based structure (GBS) platform has been widely constructed offshore in support of exploring and drilling activities for oil and gas industry. The aim of the present study is to investigate the wave-induced instantaneous liquefaction of a poro-elastic seabed around a GBS offshore platform, including the consideration of the effect from the platform deck. Our approach is using an integrated three-dimensional numerical model that developed based on the Finite Volume method (FVM) in OpenFOAM. In addition, a protection system for the GBS platform has been proposed and its effect on the prevention of the wave-induced momentary liquefaction have been demonstrated. A series of simulations are performed, including a consolidation process, the fluid–structure–seabed interactions and the wave-induced liquefaction and shear failure near the GBS. Numerical results reveal that the proposed protection system can significantly reduce the wave forces and the liquefaction depth in front of the platform. The parametric study reveals that the wave height and current velocity have significant impact on the seabed liquefaction in the vicinity of the GBS offshore platform. The protecting effect of the protection piles decreases with increasing of the column spacing and the distance from the GBS.

Cnoidal Wave-Induced Residual Liquefaction in Loosely Deposited Seabed under Coastal Shallow Water

This study is aimed at numerically investigating the cnoidal wave-induced dynamics characteristics and the liquefaction process in a loosely deposited seabed floor in a shallow water environment. To achieve this goal, the integrated model FSSI-CAS 2D is taken as the computational platform, and the advanced soil model Pastor–Zienkiewicz Mark III is utilized to describe the complicated mechanical behavior of loose seabed soil. The computational results show that a significant lateral spreading and vertical subsidence could be observed in the loosely deposited seabed floor due to the gradual loss of soil skeleton stiffness caused by the accumulation of pore pressure. The accumulation of pore pressure in the loose seabed is not infinite but limited by the liquefaction resistance line. The seabed soil at some locations could be reached to the full liquefaction state, becoming a type of heavy fluid with great viscosity. Residual liquefaction is a progressive process that is initiated at the upper part of the seabed floor and then enlarges downward. For waves with great height in shallow water, the depth of the liquefaction zone will be greatly overestimated if the Stokes wave theory is used. This study can enhance the understanding of the characteristics of the liquefaction process in a loosely deposited seabed under coastal shallow water and provide a reference for engineering activities.

Meshless Model for Wave-Induced Oscillatory Seabed Response around a Submerged Breakwater Due to Regular and Irregular Wave Loading

The evaluation of wave-induced seabed stability around a submerged breakwater is particularly important for coastal engineers involved in design of the foundation of breakwaters. Unlike previous studies, a mesh-free model is developed to investigate the dynamic soil response around a submerged breakwater in this study. Both regular and irregular wave loadings are considered. The present model was validated against the previous experimental data and theoretical models for both regular and irregular waves. Parametric study shows the regular wave-induced liquefaction depth increases as wave period and wave height increase. The seabed is more likely to be liquefied with a low degree of saturation and soil permeability. A similar trend of the effects of wave and seabed characteristics on the irregular wave-induced soil response is found in the numerical examples.